Generator Size Based On Average Kilowatts

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I'm thinking of getting a propane-powered whole-house backup generator with the automatic switch on when the power fails. I went through the electric bills for the last twelve months and found that we used an average of 54.9 kilowatt hours per day or about 2.3 per hour. Quite a bit, but we have a we ll with pump and my wife keeps the greenhouse warm all winter with an elect ric heater.
I have a little gas-powered generator rated at 6,500 watts that I use to po wer the pump, boiler, refrigerators, etc., but it would be nice not to have to run out in the rain to start and fuel it during an outage.
I've read that an 11,000 watt unit should be enough to power a house, and w e wouldn't be using the electric oven or dryer during outages. That would b e almost 5 times the average usage, which should give coverage for start-up peaks.
Does anyone have any official formulas for this sort of thing?
Paul
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wrote:

There really isn't a formula that will convert your average or daily usage into a number for a genset. You really have to figure out your worst-case emergency usage and then scale that depending on what sorts of loads that you anticipate using. All loads are not equal. Motors need a lot of juice to start, for instance. The genset has to handle the *peak* not the average. You also have to scale the genset for the difference between kW and VA. The electrician doing the work should be able to give guidance, given your anticipated usage.
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On Mon, 26 Aug 2013 19:47:22 -0400, snipped-for-privacy@attt.bizz wrote in
Based On Average Kilowatts:

All good advice. To OP: is the 11Kw gen rating for gas or propane? If for gas, remember that when running on propane, you will get less than the 11Kw, so choose size accordingly.
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Another question is the quality of the propane generator. I can't remember the details, but some brands are very poor quality. Not likely to last very long, and won't put out good quality electricity. Makes a bit of snow on the television picture. What's a backup generator, without television?
. Christopher A. Young Learn about Jesus www.lds.org .
On 8/26/2013 7:47 PM, snipped-for-privacy@attt.bizz wrote:

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On 8/26/13 6:28 PM, Pavel314 wrote:

I wonder if you'd be better off with a propane heater for the green house at least for the times the power is off.

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On Monday, August 26, 2013 8:31:47 PM UTC-4, Dean Hoffman wrote:

That would probably be more efficient, burning the propane for heat directly as opposed to converting it to electricity to run the heater.
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On 8/26/2013 6:43 PM, Pavel314 wrote:

Divert the engine cooling air thru the greenhouse. And run the exhaust thru a heat exchanger and use that to heat the house.
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You're on to something. During a power cut, it's wise to modify your power usage. Cook with gas, clothes line dry the laundry or delay the wash till the grid power comes back on. So, the backup generator can be smaller. And the family need to know the power hog devices, and not to use them on generator power.
In the long run, changing the greenhouse to vented wall heater may save a lot of money. Electric heat is very expensive.
It's really nice to be able to run refrigeration and AC, but they have a heavy start up current.
. Christopher A. Young Learn about Jesus www.lds.org .
On 8/26/2013 8:31 PM, Dean Hoffman > wrote:

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In your case the average would be like sticking your feet in boiling water and putting liquid nitrogen on yur head. The average would be 70 deg, but you would not like it.
Go here and add up all the wttages of everything you may have on at one time. http://powerequipment.honda.com/generators/generator-wattage-estimation-guide
This will give you a rough guide. If your 6,500 unit is powering everything you need now, the 11,000 gas will be plenty.
Just remember the larger the unit, the more it costs to run. Check out how much the unit will cost to run before you make the final decision.
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On Monday, August 26, 2013 8:38:15 PM UTC-4, Ralph Mowery wrote:

Thanks for the link.
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Pavel314 wrote:

My Generac is only about 8KW and it is far more than I need when the power goes out.
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Per Pavel314:

Not me, but I would suggest that a smart transfer switch could reduce the size of generator needed - or compensate for an error in buying one that is too small to take everything the house is going to throw at it.
A smart switch will turn off specified circuits for a specified time in order to free up watts for other circuits' momentary demands.
The one I got didn't cost all that much more than a conventional transfer switch and it allows me to run a house sans AC on a 2KW (1.8 KW steady load) generator. So I'd think the same strategy could get quite a bit out of your "little" 6,500 watt generator. Might be worth getting the switch first and seeing if the current gennie can do what you need done.
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Pete Cresswell

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On 8/26/2013 8:49 PM, (PeteCresswell) wrote:

2kw is 2000 watts

so I think his little 6500 trumps your little generator by a factor of 3.
are you sure you didn't mean 20kw?

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Jeff

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Per woodchucker:

No. During outages I run the house on a Honda EU2000, which is rated at 1,800 watts continuous.
Needless-to-say, we don't even think about having air conditioning or electric cooking.
For cooking I've got a half-dozen little propane bottles and a couple of screw-on stove burners for them - which I run on a picnic table on the patio just outside of the kitchen. I've also got an el-cheapo low-wattage microwave stored in the garden shed.
But the rest of the house manages to get buy.
If somebody forgets and tries to make toast or turns on a hair dryer or some other electrical/heat appliance (most of which pull 1,500 watts), the APC panel will shut off other circuits for a predetermined time and then attempt to bring them back online - hopefully after the offender realizes why most of the lights went out.
I've tried this in test a few times and it works. In practice, it has yet to happen except for the kitchen refrigerator - which is an old unit that pulls some ungodly amount of watts when it starts up before throttling back to about 130 watts. For that, the smart switch turns off the rec room (where my computer stuff is - all hooked up to battery-powered UPS units) for a few minutes and then brings it back on line after the refrigerator has gotten it's startup surge.
"Lifeboat".... not "Cruise Ship".
If I wanted more capacity and were going to stay with gasoline, I'd buy another EU2000 because those things can be run in parallel so the house sees just one generator. It would also let me be a Good Guy in an extended outage where other people's freezers/refrigerators needed a fix.
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Pete Cresswell

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On 8/26/2013 4:28 PM, Pavel314 wrote:

As others have stated, it's about the peak, not the average. You already have a system that meets your needs.
If you don't wish to be inconvenienced by the outage, you need to add up the PEAK numbers for everything you want to run simultaneously. Then add some slack for motor starting peaks. Then add some more for future possibilities. That gives you the size generator you need.
The bottom line is that it's gonna be a BIG number.
Divide that by the number of outages you expect. That gives you the cost of being too lazy to go start the generator you have.
Then you imagine you can manage your usage during an outage to reduce the peak need. You'll find out that the inconvenience goes up faster than the generator cost goes down.
So, you decide that you'd get more bang for the buck by buying a boat or a motorcycle or taking a vacation... and a raincoat for those power outages. ;-)
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I think anyone who tries to maintain all the comforts during a power cut, is likely to be mobbed and beaten senseless by the creatures who live in his hood. The modern view is that we all need to suffer together, regardless that the person worked hard, saved his money, stayed home and ate sandwiches instead of fancy diners, and worked to buy a backup generator.
. Christopher A. Young Learn about Jesus www.lds.org .
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On Tuesday, August 27, 2013 7:42:47 AM UTC-4, Stormin Mormon wrote:

My hood is mainly folks like me and most have their own generators. They put in a McMansion development up on the ridge a few years back but I think a few rounds of .308 would convince them to go back home and freeze in the dark.
Paul
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I think there are different type of people. Me, living in a trailer park of day to day people. I do what I can to prepare for when things go wrong. Others around me live for the moment, from what I can tell. My guess is that the Mc Mansion people also live for the moment.
. Christopher A. Young Learn about Jesus www.lds.org .
On 8/27/2013 9:38 AM, Pavel314 wrote:

own generators. They put in a McMansion development up on the ridge a few years back but I think a few rounds of .308 would convince them to go back home and freeze in the dark.

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Per Stormin Mormon:

Somebody on this list observed the distinction between "lifeboat" and "cruise ship".
I opted for the lifeboat approach based partially on fuel consumption.
If I had the sense to get a nat gas install, that would not be a consideration - but I bought a little Honda EU2000 that runs on gas and gets about five hours run time per gallon. My neighbor's el-cheapo 6,500 watt gennie gets more like five gallons per hour... OK, that's an exaggeration.... but it does drink gas.
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When the power is out, often the gas stations are unable to pump fuel. Best to have a system that runs as long as possible on fuel.
Years ago, I worked the numbers. IIRC, a gallon of gasoline puts out 2,000 watts for 1 hour.
. Christopher A. Young Learn about Jesus www.lds.org .
On 8/27/2013 11:05 AM, (PeteCresswell) wrote:

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