General Question

janbb's avatar

How big a standing generator would I need to get?

Asked by janbb (44243 points ) November 15th, 2012

Thinking about installing a natural gas automatic switch generator. Price seems to vary greatly depending on kilowatts. Wondering how big a generator I need for a two story, 1800 square foot house?

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15 Answers

Brian1946's avatar

I’m going to summon someone more qualified than me to answer this, but in the meantime, doesn’t your electric bill show your monthly kilowatt consumption?

janbb's avatar

Will have to check. I don’t look at the bills since they are paid electronically by someone else. (And I just sent this to LuckyGuy as well.)

Brian1946's avatar

(And I just sent this to LuckyGuy as well.)

I also sent it to him. ;-o

jaytkay's avatar

Here is an online estimator:

Kohler home generators – Sizing calculator

A friend’s off-grid cabin has a Kohler generator. He highly recommends them.

janbb's avatar

@jaytkay Thanks! I’m looking into Generacs which are cheaper than Kohlers but the calculations should work for either.

gailcalled's avatar

@janbb: And keep in mind that you can call this a capital improvement, which adds value to the house.

LuckyGuy's avatar

Two questions: Do you have city water? Do you heat with natural gas?
If “yes” to both of those questions, I would not go bigger than 8kW and actually feel 5–6kW is more than enough. This is one case where I do not believe in oversizing. You do not need to run everything in the house at the same time during emergencies. Some people (IMO with more money than brains) size the generator so the whole house works normally as if nothing happened. They pay big $$$ to have a 20kW unit installed that takes up twice the space, uses more fuel and costs twice as much. The smaller you go, the more fuel efficient you will be and the longer your back up fuel will last. My little 1.1kW does everything I need in an emergency. Can I use my electric oven? No. Can I use a toaster oven or microwave? Yes. If I turn off everything else. No big deal. I act conservatively and my fuel lasts forever! The big monsters use a lot of natural gas but you don’t notice it because it is piped in – if it is turned on. If you have a storage tank for backup, then fuel efficiency becomes important.
If I were doing it and natural gas was available, I would put in a stationary natural gas fed 5.5 kW (or similar) unit and have a 120 gallon Liquid propane storage tank as back up. I would make sure the jets in the generator could handle both. If that is not possible I would buy the proper assembly and keep it with the LP tank so I could swap it out if I ever needed it. It is a quick swap requiring only a wrench.
I would also pay $700 for a legal automatic transfer switch.
With that setup, if you lost power, within ~30 seconds the generator would start and you would be back in business. If natural gas were shut off, like on Barrier Island, you could swap out the jet and easily run for about a month if you are a little conservative. Not long enough? Then add a second tank.

My situation is different from yours. I have a wood burning stove, with an unlimited wood supply. Split and stacked for at least a full season. I also have an oil heat system and have a year’s supply of heating oil. There is enough gasoline to run the generator for at least a month. I have a well AND town water and I have plenty of food – and ammo ;-) . I am set.
You are doing a good thing!

Ron_C's avatar

I have a high efficiency gas hotwater heating and hotwater system and a 3500 watt generator. We also have LED lights and don’t heat rooms that we aren’t using. I also have a non-venting gas heater in the garage with a small fan to circulate heat.

I can hardly wait for power outages!

LuckyGuy's avatar

@Ron_C That is a perfect setup. It is sized just right and you know how to be careful. Do you have backup fuel (bottled LP gas) in case natural gas is shut off?

Some people buy units that are 6x your size just so they can continue to air condition their entire house. It’s ridiculous. If you really need air conditioning, a small window A/C unit for $90 will cool a room and only needs 1 kW. A little common sense goes a long way.

WestRiverrat's avatar

I have all electric heating, I have a portable 3.5kW generator that I use to run a couple space heaters in the bathroom and the kitchen to keep the pipes from freezing. If the power is out I close off the rest of the house and sleep on a cot in the kitchen.

There is enough extra power to run a light, phone, and a radio or the microwave. It is not hooked into the power grid, I run an extention cord with a power strip at the end out the window, and keep 15 gal of gas for the generator.

janbb's avatar

Since I live alone, I don’t want to have to worry about buying gas or setting up and starting a portable generator. I do have natural gas and city water. I am thinking about an automatic system that is plumbed into the natural gas. What you said makes sense, Lucky.

jerv's avatar

I agree with @LuckyGuy; figure out what is important and buy a generator big enough to power just that. When I was in the Navy, the first thing we did when the main generators went out was to turn off all non-essential loads; if we were on emergency generators, no Xbox; that circuit is dead. The same applies to homes. Just enough to run the bare necessities. How much that is…. well, without seeing your house, one can only guess.

FWIW, my little cabin in the NH woods did fine with an 1100W.

LuckyGuy's avatar

@janbb Get one with auto start, auto transfer switch, auto testing, battery backup, plumbed into your natural gas line. That is perfect. Don’t let them talk you into something too big.
Like @jerv said you need to power essentials. The rest is just luxury.
I’ve said this in another thread but it is worth repeating: my 1.1kW powers, my electric garage door opener, freezer, refrigerator, sump pump, thermostats, kitchen appliances and outlets for charging computers. Not at the same time, obviously, but It runs a loooong time on a gallon of gas.
A 5 kW would give you a lot of extra power to operate all kinds of things at home, if you are conservative. You’d be able to do laundry, turn on all your lights. watch TV, even use your hair dryer and iron. But not necessarily at the same time.
Seriously, think about adding a storage tank in case natural gas is turned off. That is the only reservation I have about natural gas power. I’ll bet there were more than few people on Barrier Island cursing the day they spent good money for that nice new natural gas generator that did not work because the gas was turned off. .

janbb's avatar

I went to Home Depot and someone will be calling me to come out and give an estimate. The prices on the Generacs were less than I expected but they didn’t give installation figures.

WestRiverrat's avatar

Once you figure out what you need, ask about prices for the next size up too. That is why I got my 3.5kW. It was cheaper than the smaller one that I __needed__, have to love clearance sales.

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