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Old 07-30-2010, 12:46 PM   #1
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How to determine power requirements for a generator and other questions


So now that I understand that I can't place a gas-powered generator inside my house, I will need to figure out where I would put it on the outside (since there is relatively little available space).
- The 1st question is how powerful should the generator be. To determine the max Watt requirements, can I simply take every breaker in my breaker box, multiply its amperage (say 15 amps) by 110 Volts and get the power needed by all the electrical pieces that sit on that breaker? I would then sum up the numbers for all the breakers, or just those that control vital equipment (e.g. fridge + AC + some lights in the summer) to get the max wattage the generator should produce?
- In general, given the same power level of a generator, does one powered by natural gas take more/less space, generate more/less heat, is more/less noisy, more/less reliable, more/less expensive to operate than an equivalent one that uses diesel fuel?
- How close/far can the unit be to the house? How much empty space should there be around the unit?
- Any other aspects I should consider?

Thanks much!
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Old 07-30-2010, 08:37 PM   #2
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Well it all depends on what you want the generator to do. Do you want it to run say the heat and a few lights and plugs? Or do you want it to transfer your whole house? The bigger the generator the more money it's going to cost you.
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Old 07-30-2010, 09:23 PM   #3
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The bigger the generator the more money it's going to cost you.

and the more space it is going to take up.
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Old 07-30-2010, 09:30 PM   #4
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If you want stand by unit on Natural gas I know most common size useally anywhere from 7.5 to 15 KW { kilowatts } is common and you will have choice of transfer switch it will have in automatic or manual.

all it depending on how you want to set up if pretty much bell and whistle type it will cost more than plain jane units.

The stationary units are not really super loud if have proper sound enclosure I know with some package it will be quite as gaz powerd car at idle or at fast idle.

The bigger unit it get the more it will cost not only the generator but you have to look at the gaz piping size as well that will affect the cost as well.

Plus I know most building codes that you have to keep the generator anywhere from 18 to 36 inches from the house { depending on the state codes }

Merci.
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Old 07-30-2010, 10:42 PM   #5
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To run a fridge and a window AC and a few lights you might need 2 kW steady draw or 5 kW peak, so a 5 kW gen. might work, $600 from HD for a gas model.
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Old 07-30-2010, 10:47 PM   #6
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Quote:
Originally Posted by Yoyizit View Post
To run a fridge and a window AC and a few lights you might need 2 kW steady draw or 5 kW peak, so a 5 kW gen. might work, $600 from HD for a gas model.
I can run my central AC, water well pump, any/all lights in my house, a couple of floor fans, refrigerator, 2 televisions, computer all at the same time on a 5kW gennie. If I turn off my AC I can run my (electric) water heater.
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Old 07-31-2010, 10:47 PM   #7
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5 KW running central air?? I find that very hard to believe.
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Old 07-31-2010, 10:59 PM   #8
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5 KW running central air?? I find that very hard to believe.
Not really if a small central air like two tonne unit it may be a doable depending if it have soft start kit allready installed.

Merci.
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Old 07-31-2010, 11:50 PM   #9
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Quote:
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5 KW running central air?? I find that very hard to believe.
Quote:
Originally Posted by frenchelectrican View Post
Not really if a small central air like two tonne unit it may be a doable depending if it have soft start kit allready installed.

Merci.
Marc
It's either a 3 or 3 1/2 ton. Can't remember off the top of my head. and no, no soft start.

whether you find it hard to believe or not doesn't change the fact it is true and don't forget, that is while I am using a lot of lights, television, computer, refrigerator and water well pump. Actually, I was pleasantly surprised when it showed it had no trouble running all of that. I didn't expect it to be able to carry everything it does either.

the only thing I have to do is shut it down the AC when I want to run the water heater. Other than that, that 5kW gennie puts me just like POCO power (other than the noise and filling up the gas tank)
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Old 08-01-2010, 09:45 AM   #10
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Quote:
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I can run my . . .
5000 W/240 V = 21 A. I'd think your central air uses this much current all by itself.
Maybe your generator's circuit breaker contacts are welded closed.

Can you post a link to your generator?

Last edited by Yoyizit; 08-01-2010 at 10:02 AM.
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Old 08-01-2010, 10:10 AM   #11
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I agree with the others. Nap's situation is VERY unique, I have never seen anything like that in many, many generator installations. Please don't judge your own system by his experience, or else you will be disappointed.
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Old 08-01-2010, 02:05 PM   #12
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Quote:
Originally Posted by Yoyizit View Post
5000 W/240 V = 21 A. I'd think your central air uses this much current all by itself.
Maybe your generator's circuit breaker contacts are welded closed.

Can you post a link to your generator?
apparently I can't. It is very similar to this unit but it is rated for 5kW/8kW surge. The one in the link is 8/10

http://www.ruralking.com/generator-8...lec-start.html

and anybody is welcome to come on over for a demo. I don't drink beer but I do eat filet mignon`.

and to the welded breakers; I have tripped out the unit before. That is how I fugured out I had to turn off the AC when I wanted to run the water heater.

Last edited by nap; 08-01-2010 at 02:07 PM.
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Old 08-01-2010, 02:56 PM   #13
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it sort of makes sense. with the 8kw surge it would take lot to pop it. i would suspect that the compressors in the fridge freezer and the ac would all have to fire at the same time to trip it. An ac unit may be rated for 30A but i've come accross quite a few rated at that but have been miswired for a much smaller amperage and operate fine( this is not to say it's safe). Throw an ampmeter on a 3 ton unit and i bet you see it's running at about half of what it's rated breaker is. So lets give that about 15A or so. That leaves about 15A @ 120v to run the rest of the stuff and it's not that big of a stretch.
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Old 08-01-2010, 03:02 PM   #14
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Now I can see the whole picture how it layout and that is pretty good size unit that can able run the A/C unit 8KW surge that will start the A/C up but once it get running it is not too bad.

Merci.
Marc
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Old 08-01-2010, 10:42 PM   #15
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What is the SEER of your AC unit? I have a newer one: 3 ton, 18 SEER. I doubt that even a 10 kW unit could start this one.

My APC/UPS box bleeps every time the AC kicks in, due to the sag in utility power ....
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