Posts Tagged ‘backup generator’

Harbor Freight 800 Watt Generator

July 21st, 2012 No comments
This entry is part 6 of 9 in the series Generator

Harbor Freight 800 Watt Generator

I needed a small generator for an upcoming camping trip. And my every other day Harbor Freight sales e-mail arrived in my inbox. So I took the plunge on this popular little generator. The first one didn’t work out so well (ahhh, Harbor Freight, you never fail to fail). But the second one seems to be working. Read all about it – I gave the generator its own review page here.

How Long Will My Generator Run?

September 6th, 2011 9 comments
This entry is part 5 of 9 in the series Generator

Hurricane Irene just wandered up the east coast and once again my house was spared from any significant problems. We lost power for about 11 hours, but that was nothing compared to my neighbors, many of whom were without power for days. Luckily, I have a 12 KW whole-house generator. And because Verizon kept the FiOS TV and Internet going full speed for the entire storm I spent the day watching Looney Tunes with my daughter and surfing the net for information. My neighbors spent it manually bailing water out of their basements.

The day after the storm traffic to my generator article doubled. Go figure … I suspect generator sales will increase too. But one reader made left an interesting comment: “I never see anyone say how large their propane tanks are and how long the generator (a 17kva, let us say) can run on a certain quantity of LPG. Thanks!” That’s a good point. The reason is probably because the calculations can be complicated, but decent estimates can be made. Here’s how I figure it all out.

Step 1 – How Much Fuel Does Your Generator Need?

This should be a relatively straight-forward answer. Though it depends on the load at which the generator is running, ultimately this is a straight power calculation. In AC electrics, power is expressed as kilovolt-amperes or kVA. In some instances one kVA = one kilowatt or kW. But for some types of loads (capacitive rather than resistive like a motor versus a light bulb) something called a “power factor” must be taken into consideration. In these cases, 1 kVA may equal more than 1 kW. Why does this matter? Because the fuel your generator consumes depends on the load or the number of kVAs it is driving at any time. But most generators are rated in Watts. If you are really concerned you can look at the specification plates on all your appliances and add up the kVA loads and do a conversion to kW. Or you can assume that the overall power factor for your appliances will be pretty close to 1 and just assume 1 kVA = 1kW. That’s what I do. Ultimately you could calculate the power required to run what you want to run, add a bit for the inefficiency of the engine and alternator, and then calculate how much fuel is required to deliver that much power.

The easier way is to let the generator’s engineers do this for you. Somewhere in your generator’s manual there will be a chart that shows fuel consumption versus load. Mine looks like this (found on the second page of my manual at

Load (%)Fuel Requirement (Propane)BTU / hour Required
25% (~3 kVA)45 ft3 / hour72,500 BTU/hour
50% (~6 kVA)60 ft3 / hour90,000 BTU/hour
75% (~9 kVA)75 ft3 / hour112,500 BTU/hour
100% (~12 kVA)81 ft3 / hour180,000 BTU/hour
Fuel consumption of a Kohler 12RES generator.


Then it’s just a matter of figuring out your load, converting the cubic foot measurements to gallons, and voilà, that’s how much fuel you will burn. Except it’s not really that easy … the exact expansion of a gallon of liquid propane to a volume of gas is governed by things like temperature and pressure (remember the Ideal Gas Law from high school physics? PV=NkT? This is why you should have paid attention.) Since propane techs have better things to do than run around with cheat sheets listing the Boltzmann Constant and Avagadro’s Number, they take temperature and pressure out of the equation and work with the actual energy requirements needed rather than volumes. These are listed in column 3 of my chart and are based on the approximate energy value of a cubic foot of propane listed in the Kohler manual.

Thus, at 100% load (the worst case scenario) my generator needs 180,000 BTU per hour to run. The National Propane Gas Association lists one gallon of propane having 91,502 BTU. Thus my generator will need to vaporize and burn approximately 2 gallons per hour at full load. (Or, a bit more accurately, 1.97 gallons per hour.)

Step 2 – How Much Gas Do You Have?

My Dual 125 Gallon Tanks

This seems like a simple question, but it isn’t. My installation has two 125 gallon tanks (420 lbs. capacity each). So it might seem like they could hold a combined 250 gallons. Which, at the approximate 2 gallon / hour rate calculated above would mean that my generator should be able to run at 125 hours (~5 days) at full load on two full tanks. But that isn’t even close.

Propane is stored as a liquid. It must become  vapor before it can be used. To do this, it must absorb heat and then transition from the liquid to the gas phase. Gasses occupy many times the volume of liquids, so in order for this vaporization to occur, the gas needs a space into which it can expand. In a gas cylinder, this is called “headspace,” and it means that my 125 gallon bottles can never be filled to the top. Some room must be left for the gas to expand.

As a general rule, propane cylinders are only filled to 80% of their maximum capacity to allow for expansion of the liquid and enough headspace for the gas. Thus, each cylinder can only hold a maximum of 100 gallons of propane (125 gallons * .8 = 100). So when the fill gauges are pegged at 80% I have 200 gallons to work with or approximately 100 hours at 2 gallons per hour full load. See, we already lost a day of runtime. 100 hours is approximately four days, if we could drain the tanks completely dry.

But guess what – we can’t drain the tanks dry. There are a number of reasons for this. In ideal conditions, there comes a point where the empty volume of the cylinder is so large compared to the amount of propane left that even if it were to all vaporize it wouldn’t generate sufficient pressure to push out of the cylinder. And this can be exacerbated if the temperature drops as it does here in a Massachusetts winter.

So another rule of thumb is that you will never draw a cylinder down below 10% of its rated volume. Thus my 125 gallon tanks will always run out with about 12.5 gallons left in them. If they only start with 100 gallons each, and we can only draw until 12.5 are left, that leaves 87.5 gallons of usable propane in each tank or 175 gallons of total usable propane. That means that in a perfect world I have 87.5 hours running at full load, or just over 3.5 days.

Step 3 – Can You Really Generate the Gas Needed?

If you live someplace warm, the answer to this question is yes. Those of you in Tampa Florida can pretty much stop reading now. Just divide the amount of gas you have by the consumption per hour and there you go – that’s your runtime. But those of us who live in cold climates have an additional concern. The factors here are complicated, but essentially come down to this:

Can your gas system absorb enough heat on a very cold day to vaporize the amount of propane needed to run your generator at full load?

What factors determine this? Two mainly.

  1. The “wetted surface area” of your tanks. The wetted area is the surface area of the tank exposed to the liquid propane contained within the tank. Obviously the wetted area decreases as propane is withdrawn, another reason why tanks can’t be drawn much past 10% capacity; on a cold day there’s simply not enough surface area available to absorb heat from the environment.
  2. The ambient temperature outside the tank. Buried tanks have a distinct advantage in the winter versus tanks exposed to the weather.

This may help to answer an obvious question: why does my installation have two 125 gallon tanks rather than a single 250 gallon tank? The answer is that two 125 gallon tanks have a greater surface area, and a greater wetted area per unit of propane volume, than a single larger tank. This helps ensure that my system can generate the necessary gas volume even on the coldest day.

How can you figure out if your system will generate enough? Rego Products is a company that makes propane regulators and fittings among other things. They publish a handbook for propane installers which has some handy equations. The most useful appears on page 7 which lists the “rule-of-thumb” for calculating propane vaporization rates and correcting for temperature and cylinder volume (wetted area).

It looks like this:

Vaporization rate (in BTU / hour at 0°F) = cylinder diameter in inches * length/height in inches * percent volume correction constant * temperature multiplier.

Update (10/2/2012): I built a simple online calculator that will do this math for you. Enter your cylinder sizes and it’ll tell you how much energy your system can deliver at a given temperature and gas level.

Part 4 – My Particular Situation

In the summertime I don’t have much to worry about. I’ll get the 3.5 days at full load without trouble, and much more if I am careful with the appliances. In winter, the concerns are different. Rather than list all the constants and corrections here, please visit the Rego book and see for yourself. I will calculate the worst case scenario: -5°F weather and a full generator load all the time.

With full a full cylinder my calculation is:

2 * (30″ * 54.5″) * 100 * .75 = 245,240 BTU / hour generated. This is well above the 180,000 BTU / hour required at full load we calculated above. So, with full tanks, we know my generator will run at full load for some amount of time even if it’s -5°F out. What about at the end of a tank though?

Repeating the same calculation for a cylinder only 10% full I get:

2 * (30″ * 54.5″) * 45 * .75 = 110,362 BTU / hour. Uh-oh. My generator can’t run at full load at -5°F when the cylinder is at 10%. But a quick look at the original chart says this is still enough to run at 50% to 60% load.

If I raise the temperature to 0°F and 10% tank volume my result is 147,350 BTU / hour, well above 75% load capacity.

The good news is that the temperature in this equation is a 24 hour average and it rarely gets below zero for even a full day where I live. On all but the coldest days of winter my generator can run for at least 3.5 days at full load. Since I can be careful about the appliances I run I rarely approach full load in winter when its cold out (I have oil heat for example). So my generator can run for more than that. How much more? A rough calculation says that at a constant 75% load I should be able to run for six days on a full set of tanks no matter how cold it gets outside.

That is a comforting thought.

Categories: Technology Tags: ,

Update on my Home Energy Monitor

September 8th, 2010 4 comments
This entry is part 4 of 9 in the series Generator

A while ago I wrote about my Black and Decker home energy monitor. I mentioned that I had problems with the sending unit leaking and then failing soon after I received it. So Black and Decker replaced the sending unit under warranty. Well guess what … the second one died about six months later. This time it didn’t leak, it just stopped transmitting. Yes I’ve changed the batteries and re-sync’d it. I’ve removed and reinstalled it. It simply doesn’t transmit a radio signal any more.

So even though I was originally pretty happy with this thing, I now recommend that you stay away from this and do not buy a Black and Decker Power Monitor. Unlike many of the negative reviews on Amazon, mine has nothing to do with setup or whether it will work on your meter. Rather, the quality of the sending unit seems poor. As always, your mileage may vary, but my experience with this unit has been bad. I think I’ll buy a TED monitor system instead.

How to Tell You Have a Good Generator Installer

September 24th, 2009 No comments
This entry is part 3 of 9 in the series Generator

I was thinking back to my post about the installation of my whole house generator (which remains very popular) and I realized that I said my installer was good, but never gave a lot of detail about how I knew. So here’s a list of things you should look for.

  1. They show up on time. If an installer makes an appointment, they should keep it or have a damn good excuse why they miss it. Like a death of an immediate family member or a car wreck good. Missing appointments is the sign of either an over-extended contractor or an amateur that can’t schedule or run a business. This is especially true for the Sales call. Hell, that’s the time when they’re trying to convince you how good and reliable they are, so if they blow this, run away.
  2. Mike_holmes_picture

    Mike Holmes

    They aren’t immediately available. As Mike Holmes, Canadian contractor, TV Host,  and advocate for good contracting says, “Pros are busy.” Good contractors are always in demand, even in a down economy. Because there are always people and companies with enough money to do a job, and in a tight economy they want every dollar spent wisely, so they keep good pros busy. If your contractor quotes you and says they can start the next day, be very concerned.
  3. They seem knowledgeable. You know a bullshitter when you hear one. A good contractor not only has opinions but can give reasons for them. Why do they prefer one brand over another? What makes one company’s product superior? Why do they sell the brands they do?
  4. You receive a detailed itemized quote. A one-line price isn’t acceptable. This job is too small for a full, formal contract, so the quote will serve as the document of record for the work to be performed and the price. And it should spell it out in detail. Like how the site is to be prepped — with gravel? Concrete pad? What will they do for a transfer switch? Will they rewire existing circuits? How will the cables be run? The more detail the better.
  5. They will pull permits. Ask the question clearly — “Will you pull necessary permits?” If the answer is other than, “Yes,” walk away. The only exception is if you are fortunate enough to live in one of the few very rural unincorporated and/or unzoned townships left in the US (like I did growing up — as far as I know there is still a “farmstead” zoning exemption in Sterling Township, PA for landowners with over 50 acres of land). Good contractors don’t fear inspectors. (Note, the generator installer might ask for the gas company to handle the plumbing permits for the gas line — but again, the gas company should have NO problem with this.)
  6. They will show you the permits. It’s one thing to say you’ll pull the permits. It’s another thing entirely to do it. Ask to see them before work starts.
  7. The install looks durable and professional. Look — this is your home, your comfort, and your safety we’re talking about. A backup generator is asked to do a terrible job. Basically, to sit neglected and unused in the elements until some calamity happens, and then run reliably and flawlessly for potentially days or weeks without stopping, poisoning your family, blowing up your delicate electronics, or burning your house down. And the only way the generator will be ready to turn on when it’s ten degrees out after sitting through five years of rain is if all the connections are sealed well, if the gas is plumbed correctly, and the system is maintained. Look to make sure that all the cables run outside are in sealed conduit, that the generator is on a stable platform, that the plumbing is secure and supported, and the inside wiring is clean and neat.
  8. They clean up. After they’re done installing a generator your house should look like it did before they started. Only with a generator.

Whole House Power Monitor

September 19th, 2009 1 comment
This entry is part 2 of 9 in the series Generator

Review of Black & Decker Power Monitor

Black & Decker Power Monitor (Display Unit)

Black & Decker Power Monitor (Display Unit)

If you are thinking about (or already have) a whole house generator, one of the things you want to know is how much power various things in your house use. So, to properly size the generator you’ll need you will want to monitor the usage of various critical appliances and circuits. But how?

There are really three ways: hire a pro, measure individual appliances and circuits, or buy a whole-house monitor. Prior to my generator installation I used the single curcuit method (with a clamp-on multi/ammeter and a plug I built myself). But now, thanks to a great 2009 Father’s Day gift, I have an always-on meter to do the whole house load for me.

Meter Background

There are really two types of homeowner meters for sale: inductive and optical. Both do the same job, thought I haven’t seen any accuracy comparisons between the two technologies. As always, each technology has it’s advantages and disadvantages.

Inductive Meters

Inductive meters consist of a sending unit that reads the current drawn through your circuit panel via inductive clamps. The most common version of this type of meter is the TED (The Energy Detective). These types of meters have several advantages over the optical kind. Mainly, inductive meters can measure a single circuit, a single sub-panel, or the whole house and, they work while the generator is running. They’re also installed inside the circuit panel and protected from teh elements. The TED also has interesting features, like holding the daily peak usage in memory so you can really see what the peak loads were over a span of time to size your generator correctly. One drawback is that you must open up your circuit panel to install this type of device, which scares a lot of people.

Optical Meters

Sending Unit Attached to Meter

Sending Unit Attached to Meter

Optical meters have a sensor that attaches to your mechanical electric meter (on the outside, no need to open it). This sensor tracks the movement of the spinning wheel inside most electric meters and calculates usage based on that. The primary advantage of this type of system is that you don’t need to open your panel to install it, and they tend to be less expensive than inductive sensors. The disadvantage is that they can only measure the whole house, and they only work on utility power. So when the generator is running you wont have a real-time readout. They also have a sending unit installed outside in the elements on the electric meter and there is a real concern that a $100 device just won’t hold up. In fact, mine came out of the box with a leaky sending unit and I needed a warranty replacement from Black & Decker.

The Black & Decker power meter is really a re-branded meter from a company called Blue Line Innovations ( and sold through various retailers. In fact, it’s an older model, because Blue Line apparently released a new version in May 2009 that adds a daily peak usage memory that mine doesn’t have. So the Blue Line site is a good place for information about the meter — better than the Black & Decker site. But nonetheless, it gets the job done for just over $100 from


Rating: ★★★★☆ 

Setup wasn’t that hard. The manual is very thorough and it walks you through the calibration without too much fuss. Installing the sending unit wasn’t that hard either, though this can vary depending on meter type. In my case (a 30 year-old meter) it was as simple as tightening a large hose clamp around the meter glass and aligning the sensor arm.

You will need an electric bill because the meter calculates cost based on power used and it therefore needs to know cost information. This shouldn’t be too hard to find on most bills. There are four or five steps needed to calibrate the meter depending on how your electric rates work. But once done the receiver can give you an idea of how much your use costs. It even has a function that will predict your monthly cost depending on the usage patterns it has tracked.


Rating: ★☆☆☆☆ 

Once I got mine installed and calibrated, it seemed to perform fine. The receiver captured and held a signal about 30 feet away, through several walls. But even with a really old meter, which tends to get fogged a bit during high humidity, the sensor keeps reading the values and gives me a realistic (I can’t really judge the accuracy) picture of usage. It definitely changes values when my electric stove or dryer turn on, and it also cycles in time with my electric oven when the heating element comes on and off. So I have every reason t believe that the display is reasonably accurate.

One problem it does have is frequent dropping of the radio signal. The receiver needs to be re-sync’d frequently.

Breakdown and Replacement

Rating: ★★☆☆☆ 

However, one problem became apparent soon after installation: the sending unit simply stopped working one day. We had a very wet summer this year and when the sensor stopped sending one day the first thing I thought of was that it had leaked water. Sure enough, when I opened the battery compartment, which also houses the main circuit board, several drops of water leaked out. I took the sensor inside and let it dry for a couple of days and it came back to life. So I reinstalled it, tightening the cover extra tight in the hope that it was a leaky silicone gasket letting the water in. It wasn’t, and the sensor failed again during the next rain storm.

I called the 800 number on the front of the instructions and had some confusion navigating the menu (it announced itself for DeWalt tools, not B & D). But eventually I got to an operator and gave her the product number. Clearly this line handles all the B & D products from power tools to coffee makers, and there was no way that an operator would have any idea about the product I was describing. But she was polite and indicated that if they authorized a repair I would hear via a return phone call in a couple of days. Well, I didn’t. But abour a week later I received an envelope that had a B & D shipping label inside, with absolutely no instructions whatsoever. So I assumed that they wanted me to send this thing for repair, which pissed me off, since I really wanted a replacement and didn’t want to wait 6 weeks for a repair to be done.

But then, another week later, a UPS truck stopped one afternoon with a box and inside was a complete new unit! And again, no instructions about what to do with the old one. So at this point, I have two units, with one working sending unit. And as soon as B & D tells me whether to actually ship the old one back, I will.

Update: 9/8/2010 – B&D never asked for the old one back. I wish they would have though, because 6 months after getting the replacement sending unit running, it too failed. This time there was no water leak, it just stopped sending data. I wrote a brief, separate update here.

Overall Impression

Overall: ★½☆☆☆ 

Basically, now that after the quality problem has been solved once, I am happy with this meter. the second transmitter broke in a few months. It was easy to install, reasonably sensitive, the receiver works at a good distance, and I have every reason to believe that it is reasonably accurate. Given the initial failure that I had, I do worry about the longevity of the sending unit while it’s exposed to the weather. And I would prefer a unit that would work while my generator is running to help me monitor the load. But as a gift for around $100, I really can’t complain. feel like I’ve been ripped off due to the poor quality.

Black and Decker tech support was very confusing, but in the end it served its purpose and got the job done. I received a replacement unit and everything works. and everything worked for a few months until the second transmitting unit failed. Now I’m changing my tune – avoid this product; it’s unreliable.


The instruction manual warns that the meter could suffer interference from certain other wireless devices. In my case that appears to me the rain gauge for my Oregon Scientific Wireless Weather Station. So even after I received the replacement unit, the display seems to go to zero whenever it rains. But unlike before when the sending unit was leaking, the display comes right back soon after the rain stops. Since the other parts of the weather station (the anemometer, thermometer, and barometer) work all the time, I assume that it is the rain gauge transmitting that interferes with the display. I’ll keep an eye on this, but I’m 99% sure that it the problem.

Categories: Technology Tags:

Whole House Generator Installation

June 30th, 2009 56 comments
This entry is part 1 of 9 in the series Generator

Life with a Kohler 12RES (12 KW) whole house backup generator.

  1. Background
  2. Decision to Buy
  3. Installation
  4. Review

(7/9/2009) When I originally wrote this I had no idea it would become the most popular post on this blog. Please — I’d like to improve it and make it more useful. Post comments if there are areas you’d like me to add or fix.

I spent a large part of my life growing up in rural Pennsylvania. I actually split my time between suburban New Jersey where I went to school and an 80 acre farm approximately 40 miles from Scranton, PA at the northern end of the Pocono mountains. For most of the time that my family owned it, the farm had a single house originally built in the mid 1800s. It sat up a 1/2 mile long driveway off of a dead-end dirt road. The power lines ran cross country to the house, and needless to say, with few customers in this area PP&L (Pennsylvania Power & Light) wasn’t interested in responding to calls at a moment’s notice. Which meant that we spent a lot of time without electricity. And I don’t mean one hour interruptions either — I mean that the place was without electricity for a full week at least once if not two or three times a year.

When I was young, this was a workable arrangement for my family, but once I left for college (I’m an only child) and my parents started aging, they couldn’t go for days on end carrying buckets of water from a surface well to the toilets to flush them (or head to the outhouse in the back yard in winter) or devote the time to splitting, stacking, and carrying enough firewood to keep the stove burning for 7 days straight in the winter. So they eventually built a second, modern ranch-style house and had a generator installed. This setup consisted of a 7.5 KW gasoline-powered generator located on a concrete pad outside the back door and a manual transfer switch in the basement connected to a panel which ran a few lights, the water pump, the furnace, one light or outlet in each room (including one for the refrigerator in the kitchen), and an extra outlet in the living room for the TV. Since they cooked with a gas stove, they were also able to cook.

This was a dramatic improvement, but still not an optimal solution. By today’s standards it was a terribly inconvenient installation, primarily because it meant that my parents had to constantly pour gasoline into the thing to keep it running (about every 8 hours at a moderate load), even though they cooked and heated with propane and had a giant bulk tank right in the driveway. Plus, a manual transfer switch isn’t fun for young people, never mind my almost elderly parents tromping down to the basement by flashlight in order to throw this thing on and off.

So, when I bought my latest house in Massachusetts and my parents sold the farm in Pennsylvania, we used some of the proceeds to investigate a new generator.

Right about the time that I started research, whole-house generators were gaining popularity. The largest manufacturer, Generac/Guardian, started to put commercials on major TV networks showing people making margaritas with a blender during a major thunderstorm that knocks out power to their neighborhood. Sounded good to me.

I researched brands, sizes and types and learned a few things along the way. I quickly established that I was interested in a whole-house unit with an automatic transfer switch. I had no desire to tote large tanks of gasoline around and constantly fill up a small portable unit. Nor did I want to worry that my pipes were freezing while I was on vacation because even with a generator there would be no one around to plug it in and run it. So a propane fueled whole-house system was what I focused on. Here are a few things I discovered along the way:

  1. The market for residential systems is dominated by Generac/Guardian and Kohler.
  2. Other than the manufacturers, there is almost NO information on the web about installing or living with a residential generator.
  3. There are very few installers who deal with residential generators and the special concerns that accompany a residential (as opposed to a commercial) installation. Like siting the generator so it doesn’t piss off your neighbors, and taking the aesthetics and usability of your yard into consideration.
  4. Most propane/gas companies are useless when inquiring about these units, even when they sell them. Only a good propane supplier will take the time to work with you for little return. After all, if the generator is all you run with propane, you will be a very tiny customer for them.
  5. Many small town inspectors outside of traditional hurricane country have never seen these units and could be a significant impediment to the installation, unless they’re willing to learn and adapt like mine was.

If you are interested in a generator like this, unless you find one of the top installers in the country (like I believe I did), you had better prepare yourself for some serious learning. I believe that to truly do an installation yourself and get a satisfactory product, you will need to become familiar with:

  1. Propane measurements and usage requirements. This includes understanding bulk propane delivery units, tank sizes, headspace, vaporization rates at various temperatures, pressures, volumes, and what BTUs represent. You’ll need to make sure that your tanks can deliver the propane required to run the generator at the lowest temperature you’d expect it to run.
  2. Propane company delivery plans including renting vs. owning the bulk tanks, auto-delivery, minimum usage, etc.
  3. Flammable gas piping requirements including materials required (black iron, galvanized, other), minimum distances from ignition sources, easy access for delivery, flow rates, pipe sizes, burial requirements, etc.
  4. Generator siting requirements including gravel vs. poured concrete pads, minimum code required distance from openings (windows, doors), sound requirements, etc.
  5. Electrical codes including load requirements for what you want to power, circuit panel capacity, wire gauges vs. distances, pass through requirements, transfer switch requirements, electric company rules, etc.

For someone with no background or no desire to dive into the details, this is no small feat. And there are a few horror stories about bad installations leading to non-working systems (see this for example).

So, I went about researching and used the dealer locators to find dealers in my area that sold both Guardian and Kohler generators. In spite of being listed on the manufacturer’s website, I really had difficulty getting people to call me back (note this was 2005 during the building boom — I bet people are more responsive now). I found a dealer local to me in Massachusetts and called them. They were responsive and knowledgeable (part of a respected large electrical contractor). They came out and did an initial home survey, took pictures and measurements, and asked a lot of good questions. Then they went away and a couple of weeks later gave me a quote for over $11,000!

I had seen a company online that had a good website, but they were located almost 100 miles away in New Hampshire and I figured they would never come as far down as my area. But only because I used to live in New Hampshire and I knew where the business was I took a chance. This proved to be the single best decision of the entire process. Powers Generator Systems proved to be the kind of expert resource I needed. They were prompt, courteous, knowledgeable, flexible, professional, and … wonderful. Without question they were the single best contractor I have ever worked with. And they did the complete job for under $9000 (including gas tank costs)!

In consultation with Powers and with a little figuring about loads, I settled on a Kohler generator for a variety of reasons, but primarily because I felt that their transfer switches were more advanced and faster acting (and safer for my computer equipment), and there was (an admittedly unsubstantiated) feeling that the Kohler unit and housing were slightly higher quality than Guardian. Thus began the installation.

The following is not intended to be a step-by-step guide to installation walking you through all the possible calculations and permutations, but rather a basic outline of the steps I took to get the job completed. In order:

  1. Calculate power requirements
  2. Decide on generator size
  3. Calculate gas flow requirements and determine tank size
  4. Determine installation location
  5. Order generator and gas service and apply for permits
  6. Install gas piping and gas pipe inspection
  7. Generator site prep, installation, wiring, and run test
  8. Final propane installation & tank fill
  9. Final inspections (Fire Department & electrical)

Your actual steps may vary depending on local requirements.

Calculate Power Requirements

This is the first area where one can go astray. The main strategy a prospective generator owner needs to employ is to keep the manufacturer and dealer from over-sizing the generator you buy. Unless you have some kind of dramatic load (like central air conditioning which cycles on and off with a large current draw at startup), all the online calculators and manufacturer recommendations are designed to do two things — maximize their profit margin and limit their liability.

The method promoted by most manufacturers and installers all but guarantees an oversized installation and higher profits for both manufacturer and dealer. The typical method simply adds together the maximum capacities (amperage) of the circuits you want to power and specs a generator with enough capacity to cover them all. This maximizes profits in two ways. First, within any given manufacturer’s line of generators, different capacity generators are often built on the same basic chassis. The only substantial difference is the size of the stator winding. The incremental cost for larger stators is insignificant, yet the price difference that the manufacturer can charge is substantial. Thus, within generator families, larger generators are more profitable to sell. Second, coming to your house to conduct the power survey costs the installer money. Time spent with you is time not spent on other projects. So anything the installer can do to minimize the time spent gathering specs increases his or her profit. So what you typically get is a cursory survey that results in a larger generator than actually needed. And, by over-specing the generator they all but guarantee that there won’t be problems later when you add appliances.

A more appropriate survey adds up the actual loads which are on the circuits that will be protected and makes a realistic estimate of how often they will truly be simultaneously run. A really good survey will use an actual power monitor (like the one I have) to actually record the draw of various appliances. As an example, I have an 1800 square foot house with an electric range, electric well pump, electric dryer, and three room air conditioners in summer. By any online calculator I need a minimum 16KW generator. Yet I have had a 12KW for years without a problem. And in fact, as an experiment, I once fired up all three air conditioners (a 15,000 BTU and two 6,000 BTU units), the clothes dryer in maximum, the oven at 350 degrees, the large stove burner on high, and then made my well pump engage by running the water. The peak draw on the meter? 10.9 KW. So instead of following the manufacturers recommendation, all I need to do is not turn on absolutely EVERYTHING in the house at once and I should be fine on my 12KW unit.

Decide on Generator Size

Kohler 12RES 12 KW Generator

Kohler 12RES 12 KW Generator

I want to point our here that my original installer went with the 16KW recommendation, but it was Powers that pointed out that a 12KW would do fine. That was my first clue that they were a good company.

So I decided on a 12KW unit. If you have some additional loads, like central air or an electric water heater, then your requirements will need to account for those loads.

Calculate Gas Flow Requirements

The first step here is to find the right gas company. In the world of residential propane, generators are an extremely low volume business and therefore not very lucrative for gas companies. In most higher-volume installations, you lease the propane tanks from the gas company and pay a monthly fee just to have them. The gas company will tell you that this is for your own protection (they will change/replace cylinders when they are old and unsafe) but this is just marketing bullshit. They do it because it’s a predictable revenue stream that more than pays the cost of the tank over their lifetime and so that they can recycle tanks among customers increasing their profit even more. Most residential propane hardly notice the small rental charges on their invoices because their use of propane dwarfs the modest charge. But for a generator user who might not use more then 50 gallons in a year the cost is significant.

There are a few propane dealers around who understand this and will outright sell you the propane tanks which, although a larger upfront cost, will minimize their cost over their lifetime. Eastern Propane here in Massachusetts is just such a company, and they were the second great find during my search for help. [Disclaimer: I worked with someone for 9 years whose wife is a Customer Support manager at Eastern, so I tried them early in my search and wasn’t disappointed. But I didn’t research propane dealers nearly as much as I did generator installers.] After consulting with the Eastern representative, we agreed that for generator installs, owning the tanks is probably a better deal.

Now the arithmetic begins. Each manufacturer will provide a gas requirement as part of their installation instructions (203,000 BTU/hour for the 12RES). The key to this part of the installation is in working with your gas company to ensure that enough propane is delivered to your generator to let it start and run when needed. This is a more complicated task than it might initially seem, particularly if you live in a cold climate.

[September 2011 – I’ve written a more detailed article on gas usage and generator runtime calculations.]

Propane is stored as a liquid, but it must transfer to the vapor phase in order to run the generator. The rate that this happens is directly proportional to the heat available to make it happen which is in turn a function of both temperature and surface area exposed to the heat. This means that in a cold climate, the size of your propane bottles may be more of a function of ensuring an adequate gas flow during the minimum expected temperatures than it is of how long you might want the fuel to last. A good discussion of this is at Propane 101 and is shown in the chart below which I borrowed from

VAPORIZATION RATE – 100 lb. Propane Cylinder (Approx)

Pounds of propane in cylinder
Maximum continuous draw in BTU/hr at various temperatures in degrees F.
My Dual 125 Gallon Tanks

My Dual 125 Gallon Tanks

As you can see, the energy available to your generator at 0 degrees is dramatically different than at 70 degrees. My installation is done with dual 125 gallon (450 pound) tanks which can be seen at

Determine Installation Location

Once you’ve figured out the tank size, the next step is location. You will need to figure out the placement of the generator at the same time so that piping can be calculated. The distance between the tanks and the generator will determine the type of piping run needed. For example, codes define a maximum length of unsecured pipe, so much of your piping will need to be attached to a structure or run underground. The availability of structure to which you can secure the pipes can be a major issue (I needed to bury mine). In addition, the propane installers will worry about specific codes governing cylinder placement including minimum distances from potential ignition sources, which can include lots of stuff you probably didn’t think of like outside lighting, Bar-B-Que grills, electrical outlets, etc. And, they’re going to want the cylinders in a location that they can reach with their delivery hoses too. After your installer explains local requirements to you, you will have narrowed down the available locations for the cylinders and generator significantly. Astute readers will also have picked up on a central paradox governing this calculation. The generator itself is an ignition source! So yes, the cylinders must be both a minimum distance from the generator to prevent ignition, and a maximum distance governed by the piping required. See, this isn’t as flexible as you thought!

While siting the cylinders, you’ll need to keep in mind some things about the generator as well. The most universal requirement is that it be close to the electric service entrance to minimize the cabling required and that it must be a minimum distance from any openings to inhabited areas (to prevent the exhaust from pumping carbon monoxide into the house if you leave a window open).

Locating the generator away from the electrical service is possible, but remember that the size (diameter) of the cable run between the generator and the transfer switch will need to be increased with distance to overcome resistive losses. So there is a practical limit based on the maximum cable size that can be run. Your installer will be dealing with large bundled cables here, not typical 14, 12, or 10 gauge copper house wire.

My Generator Location

My Generator Location (see text at right for an explanation)

If you balance the propane requirements with the generator requirements, you will have few choices of where to site the units. I am lucky that my house has a detached garage connected by an open breezeway (meaning it’s not inhabited so the distance from a window in the garage doesn’t matter) and this is close to both the driveway (for propane delivery) and the electrical service. Plus it’s separated from the main house to keep the noise at a minimum.

My Installation

In the picture at left, you can see then entire installation of my generator. The path of the cable is shown as the red line. The propane tanks are located directly behind the generator, out of view of the camera. The garage is about 15′ wide, and the breezeway is 10′ wide. Where the cable runs in front of the breezeway, it’s run under some wooden stairs and comes back up to enter the basement near the meter.

Once these decisions are made, the propane installer will develop a piping plan which balances flow requirements with local codes governing pipe material and allowable distances. In many areas, codes can vary from town to town. For example, in Grafton, MA where I live only black iron pipe is allowed. But just one town over, black iron pipe is not allowed and copper must be used. Only a local expert can navigate this mess.

Apply for Permits

Once you, your generator installer, and your propane installer have all agreed on the locations for things, it’s time to place the order and pull the permits. A good installation contractor will do this for you, but it’s always a good idea to double-check and ask to see the paperwork.

Piping Install

The next step was the installation of the piping. The gas installer should have specified all the pipe sizes to be used and you will likely need a licensed plumber to do this install, or else the inspector won’t pass it. Don’t get me started on this gross restriction of freedom and total scam by states bowing to the plumbing and union lobby. But anyway, the gas company may have a certified pipe fitter on staff who will do the job. In my case, the run between the tanks needed to be buried, so the gas company gave me the dimensions for the tank placement and the generator company gave me the dimensions for the generator placement and I connected the points and dug a trench between them. The trench needed to be 40 inches deep with 6 inches of sand in the bottom. When complete, I notified the gas company and they sent the fitter to install the risers and the run between them. When done, the fitter capped both ends and pressurized the pipe with compressed air. Then he notified the town who sent the plumbing inspector to sign off on the install. As long as the line held pressure everything would be good.

Once the inspector signed off, I was free to fill in the trench (another 6 inches of sand on top and then the dirt). Then I notified the generator company that the rough piping was complete.

Generator Prep & Wiring

This was the easiest part for me because Powers generator handled everything so professionally. On the day of the scheduled install, two guys showed up on a truck with the generator. A few minutes later an electrician from Powers also arrived. I had discussed the install location with the original Powers rep, but the location wasn’t optimal and I was sure that the information about the work hadn’t reached the team.

Essentially, my installation was done on the left side of my garage. The wiring penetrates the garage, goes up and across the door header, and then down and out the other wall. From there it needed to go under some wooden steps and underground, and finally through the wall and into the basement near the main service. I was certain that no one had told this poor crew that the were going to need to remove wooden steps and trench across my breezeway plus penetrate three walls. When I met them in the driveway and explained it to them, all they said was, “Yup. OK.” And that was it. Unbelievable.

While the guys outside began leveling the pad area and dumping the gravel they brought for a base, the electrician headed for the basement. I live in a house built in 1978 that originally had electric heat. So it always had 200 amp service. But when the electric heat was removed by the previous owners, no one really cleaned up the wiring, so the 220 circuit breakers are still in the box and the old wires are hanging all around. To further complicate things, another previous owner has installed a sub-panel to power a basement workshop they had set up. This didn’t even phase the electrician who went right to work preparing for the transfer switch and the rest of the install.

Transfer Switch & Panels

Transfer Switch & Panels

At this point, I just let them work, occasionally reminding them to help themselves to the refrigerator with soda and water that was in the basement. Several hours later I heard the generator fire up (they were testing it with a portable propane tank). I went outside and was stunned at the complete job they did. The wires were run perfectly, the trench had been dug and conduit installed, everything had been sealed, caulked, and glued, and the steps had been replaced like nothing had happened. I went to the basement where a brand new transfer switch was mounted and where the circuit panel was neater because the electrician had not only done the installation, but consolidated important circuits from the subpanel to the main panel and fixed a couple of unbonded neutrals and a missing ground! They even swept the sawdust off the floor, some of which I had left there. I was utterly stunned, never having had such a professional experience.

After a few minute rundown of how things worked and how they set it up, they left me the paperwork and it was complete.

My Generator (forgive the mess)

My Generator (forgive the mess)

Final Propane Hookup

After the install was done I contacted the gas company one final time. In a few days a truck arrived with the two 125 gallon tanks and the concrete pads they would sit on. The driver muscled them into place and let me know that the final connection would be done in a few days after the scheduled fill-up. A couple of more days passed until I returned home from work to find that the tanks were suddenly full. The day after that I returned home to find that the piping was finally all connected. Success!

I simply had to try because I didn’t believe that it would actually work. So I went to the basement and pressed the button as the instructions said and the generator fired in less than 10 seconds and ran great. And it hasn’t missed a beat yet in three years!

Final Inspections

This last part was the easiest, though somewhat nerve racking. I let the town know that everything was complete and they told me that the inspector would arrive in a couple of days. True to his word he arrived as scheduled and admitted he had never seen a generator like this before. His number one concern was that there was a transfer switch to keep the generator from back-feeding the grid. He asked me about this while he was staring right at the transfer switch. Rather than be a royal pain though, he looked at the the documents that came with the transfer switch and was satisfied that it was good enough. He left without really looking at anything else. Sometime in the next few days, the final required town inspection by the fire department happened and they left a nice letter to be displayed in the window nearest the generator.

And it was all finally over!


I’d say this whole process took about 10 days of research, a week of calling companies and scheduling visits, and then about 4 weeks of work from the start of the installation to the end. It required a lot of coordination and quite a bit of research and learning.

We’ve had the generator installed for 3 years and it’s performed flawlessly. The first year was remarkably free of power failures, but by last winter the generator really paid for itself. In December we had an ice storm in Massachusetts, and while we were less affected in my town than in some areas, we were without power for 14 hours. I work in Boston and though I didn’t travel that day, while my neighbors were hunkering down figuring out how to keep the pipes from freezing, I was able to keep working online like nothing was wrong.

Update, 7/2011: It’s been closer to 5 years now that my generator has been working and I’m still satisfied. This spring there was a minor car accident on my road and someone hit a power pole with a transformer on it. As expected, my generator came on and ran for 12.5 hours. It wasn’t particularly cold out, but it was nice to be able to continue watching TV and to have a nice hot shower in the morning which many of my neighbors had to skip. And then, the most important test of my generator’s life: June 1, 2011 was game one of the Stanley Cup finals when my beloved Boston Bruins took on the Vancouver Canucks. It was also a night of tornadoes and terrible thunderstorms here in Massachusetts. And, although a tornado didn’t approach my house (the closest was about 12 miles away) the thunderstorms did cut power just before the puck dropped. Tens of thousands of Bruins fans were left unable to watch the game … but not me. Again my generator ran for about 10 hours, and I was the only house in my neighborhood with power. Miraculously, even though electricity was down, my Verizon FiOS cable feed stayed up, so I didn’t miss the game (even though the Bruins lost). Thank you Kohler!

Update, 8/2011: Hurricane Irene blew through Massachusetts and I was without power for about 10 hours. Again, my FiOS cable and Internet connection stayed working the whole day, so we weathered the storm in total comfort.

Can you see it in there ... yup, that's my car.

Update, 10/2011: 2011 isn’t going to go quietly. Just a few weeks after hurricane Irene, we had Snowtober. A freak early-season Nor’easter dropped 6+ inches of heavy wet snow on my town and because the trees still had leaves, brought down millions of branches (including an oak tree on my car … see the pic at left). Hundreds of thousands of people were without power. This time we weren’t spared … but the generator again proved itself. We were without electricity for 65+ hours with outside temperatures in the 40s. The generator ran the whole time. At one point we had some people over and the generator was holding its own with the electric oven on, two big burners on our stove on high, the well pump cycling while the shower was running, and all sorts of miscellaneous lights and TVs running. What a comfort having  this generator.

Through several short duration outages and now one that lasted several days, the generator starts in seconds and keeps the appliances running with no issues. I would do it all over again in a moment.