I need a generator to run my house on in the event of a storm or extended power outage, how do I calculate what size I need?

I can't answer how big, but if you're going to try to keep your whole house up and running normally for any extended period of time, you better have a large supply of fuel AND a big generator. Most people in this area that have a similar set up use propane fueled generators.

you're probably going to need something in the 14KW range or larger, depending on how much stuff you want to run. genrac (name brand) sells a standby for about 3-3500 which will hook up to natural or LP gas lines. they come with a switching station that will automatically start it up on the power failure event.

Some of the generator sites [Honda ?] tell you how to calculate .The problem is that there is a starting load and a running load for motors and that has to be considered.You also want to decide if it's just for 'emergency' [ only essential items to be powered].Another question is are you running electronics , computer, amateur radio etc.There you would want one that had a near pure sine wave power.
Another question , did you want portable power ? That limits it to fairly small units .
When you tie it into the power grid - Please use a licensed electrician !! Here we lost a lineman because someone decided to DIY.

i work for a Kohler generator distributor.... and i see the same quetion asked all the time... go buy a clip on amp gauge (like from a big box store)... open your breaker panel, and clip it around 1 of the supply wires to the panel... turn on everything in the house that you plan on using... record the amps used... convet the amps to watts, this will determne the kw size you need.... there's more to an energy evaluation than this, but it gives you an idea as to how its done.... pm sent...

I was looking into getting one for my place in Idaho. This was the brand most commonly used up there. I believe Home Depot is a distributor and "installer" of them. They have a sizing calculator on their site.

http://www.generac.com/Residential/

be VERY careful of installing a propane/NG generator .. after Ike, people got SURPRISING bills .. some exceeding $1500 bucks!

during Ike, I saw peaks to 6Kw, load of about 4kw ... on a 12.5kw genset ..

my advice... go large, go diesel. water cooled and 1800 RPM

Not quite that simple, diesel will not store indefinitely and unless you've got a diesel truck, what do you do with it before it gets old and algaes up? My advice, unless you're out in the boonies and use diesel for something else, don't even think about it, go propane.

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Originally posted by Boxhead:
I was looking into getting one for my place in Idaho. This was the brand most commonly used up there. I believe Home Depot is a distributor and "installer" of them. They have a sizing calculator on their site.

http://www.generac.com/Residential/

jeffe,

I do not understand. What was the $1500 paying for? Propane is THE fuel used around my Idaho neck of the woods as it is the fuel "running" the house. Just curious.

during the hurricane that houston experienced last year, the 30kw residential generators on natural gas were using $100/day in gas....pulling aroung 25kw.... when i test a generator at our shop i can use 3 gallons propane an hour on a 30 kw generator, testing on a resistive load bank, 22 kw load... it gets expensive.... as far as diesel not being stable for any length of time, there are thing you can do... buy clean diesel.... not 5 gallons at a time.... use raycor water separators on the fuel supply... keep everything clean.... if you get algae, treat it, then polish the fuel to remove the gunk... don't use additives as a cure-all... they dont work, regardless of what the mfgr's say.... they will put water or algae in solution so you can filter it out... it will not go thru the injection pump and be burned... you have to mechanically remove gunk (with filters)....

Jim:

I just looked up one 30Kw diesel generator, which the manufacturer claims burns 2.75 gallons per hour. Given that diesel is more expensive than propane currently and a helluva lot more problems to store, where is the advantage over propane, especially for urban users? While I haven't looked into it, I'm sure there are environmental considerations regarding storing large tanks of diesel inside some city limits. Burning 2.75 g/hr you'd need at least a 250 gal tank to have any real supply. I'm not arguing for propane but it is cleaner and easier to handle/store as far as I can tell.

I agree with what you say about storing and treating diesel, but all of that is a real PIA compared to propane. Finally, $100 a day to have power in an emergency is pretty cheap if you ask me. Less than a decent motel. My all electric house costs about $10 a day in the summer and that's with reasonably conservative use of power. OTOH, I've thought about a big generator and passed on the idea, the cost/benefit analysis for this area just didn't make it worthwhile to me. Barring war, we've only got two major possibilites for extended outages, tornadoes and ice storms. If a tornado hits your house, the generator is not likely to be useful and major multi-day ice storms are really rare, in spite of the fact that we were off grid for over 2 weeks starting noon Christmas Day 2000.

gato... i work the kohler dealer in houston/san antonio....im based in corpus now... the 30kw residential generators we sell have a 3600 rpm gm 1.6 liter engine on them...and they will go from propane to nat gas with just a few changes, plug or unplug 2 wires to change ignition timing and a small adjustment on the gas regulator... and $100/day is a small price to pay for creature comforts to stay at home vs a hotel....personally i have a 15kw kubota powered lima generatot that sips diesel at 3 qts/hr full load.... even then it's 18 gal day for power... sometimes a little less... 18 gal/day works out to around $50/day.... on propane the 30 kw will use 2-3 gal/hr at full load so that eguals 80-100 hrs on a 250 gal tank... if you saw what i did during the hurricane last yr, i saw people using the small recoil start gens that burned gasoline... at the rate of 40 gallons a day... that got expensive suick... not to mention the PIA to go get gasoline....a standy-by gen is a good investment....either diesel or propane/nat gas..

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if you saw what i did during the hurricane last yr, i saw people using the small recoil start gens that burned gasoline... at the rate of 40 gallons a day... that got expensive suick... not to mention the PIA to go get gasoline....a standy-by gen is a good investment....either diesel or propane/nat gas..

I used 2 5kw gens recoil start gas gens for most of 17 days and they used less than 10 ga/day each but we shut them off at night when we went to sleep.

You sell them so I can understand your POV, but I don't think most people need a standby generator, but that's each person's call based on how much money they want to pay for what amounts to high priced insurance and, of course, location is an important factor in the decision.

I would start with some information gathering:

- what is the bare minimum I have to power in the case of outage? Wattage?

- what is the blue sky; to operate without grid but everything the same. Wattage

Cost analysis for both cases and go from there. How long do you expect to be in the dark and how often it could happen, what is the loss (for instance chicken farm without power could mean all the chicken suffocate and the loss is critical)

I installed a 12kw propane generator for emergencies. Did a survey as to who was installing generators before I did mine and found out that most of the executives with all the power companies were installing them. Also found that the same power companies have not installed auxilliary equipment to handle all the home building in the last 30 years. So that told me a story, that a major shutdown was coming and soon.