generator sizing

I"m looking at generators for my house. What is the correct way to size the generator?

I am considering a PTO generator unit for a 35hp tractor. I am also looking at a standy unit that runs off the propane tank.

I would like the PTO to run:

propance furnace fan
electric water heater
sump pump
refrigerator
well pump
micro wave
general lighting
computer (home office)

A standby propane genset for the whole house would be nice, but is it really worth the money?

Quote "A standby propane genset for the whole house would be nice, but is it really worth the money?" Unquote

Yes

They are reasonable in price. Less than a 15KW pto generator + pto shaft + generator trailer + transfer switch + Murphy switch for the tractors oil pressure and coolant temp.

I must be getting old. The trip out has lost the feeling of adventure. To the shed for a tractor that is too cold to start. Then haul everything to the transfer switch in the rain or snow. Then keep checking on the tractor

With the automatic start units. You can be away or have non qualified people at home. And still prevent frozen pipes and icecream soup, anytime of day or night.

You should have a propane water heater too, even if its a small one, they have quick recovery. Hal

"Worth the money" can only be answered by you.

A cheap 4000 watt generator would do the job in a pinch if you didn't have that hot water heater and didn't run the other appliances all at once.. I used to run my house - deep well pump, fridge, oil hot air furnace, and lights with a Homelite 4000 watt (4400 surge). It worked fine.

If you already have the tractor, and power only goes out rarely, a PTO unit is the way to go. I've got a 17KW and when hooked to a 32 horse tractor - doesn't even work hard running everything in my house. PTO generators often go cheap. In fact, there's one for sale near me - today - for $350. Generac 15KW. I was tempted to buy it just because the price - but I already have two. And besides that, I'm on solar electric now with a large backup battery bank.

If you're worried about long outages - well then you've got to think about fuel and where you're going to get it. I always have 600 gallons of diesel here - so I didn'tworry about it even before I had the solar and batteries.

That's where propane might be handier if you already have a large 500 or 1000 gallon propane tank. Propane is the most expensive as far as dollar per KW ratio though. Gasoline make power cheaper, and diesel a lot cheaper. But, propane stores well - and if you already have a large tank - can be a big advantage.

The correct way to size a generator is to add up all of the wattage that you will be using together and buy a generator capable of putting out that many watts. In your case, the electric water heater is your biggest single load. Mine is a 4000 watt water heater, and my generator is rated for 5000 watts. I can therefore run my water heater with my generator, although it takes most of it's rated capacity to do so. The way I get around this is to only turn on certain circuits at a time when running the generator. If I'm not powering the water heater, I can usually run lights, furnace (propane with blower fan), TV, computer, and well pump. I then selectively switch the sump pump, and freezer circuits on in exchange for other loads as necessary. It doesn't allow the system to go unattended, but I only purchased a $500 generator that is rated for 5000 watts with a 10HP motor.
If you want to run it all at the same time, add up all of the wattage and buy an appropriate generator. At 35HP from your tractor PTO, you could theoretically power a (35HP x 746W/HP) a 26,000W generator, however because of inefficiencies the more realistic number would be around 20,000W.
Hope this helps.
Randy

As the others have said, add up all of the wattages that could be required at the same time. Add just a small safety margin; sizing a generator too large can be just as bad as sizing too small. Generators need to have a fairly good load when being used, but not an overload or a very small load.

Red, you need to decide just what it is that you SIMPLY GOTTA HAVE RUNNING AND CANT LIVE WITHOUT AND HOW LONG A DOWN TIMES YOU MIGHT BE LOOKING AT. I say that cuz that 3000 watt hot water heater is reallyyyyyyy a load, sure you need that in short term less then 72 hr emergency outages???

I say that cuz a fairly cheap 4KW can handle a lot of your needs but if you simply gotta have all that all the time you may be lookin at a better quality 6 to 7 K unit.

The other thing I would consider as far as the fuel source like how many gallons of gas or diesel or LP etc you keep on hand.

best wishes

John T

I"ve got along with a 4000watt 120/240V 8hp generator for a number of outages, over several years. No it"s not capable of running everything all the time, but I figure the generator is a stop-gap measure until we get commercial power back. My needs include refrigeration, water, (animals) and possibly heat. If you don"t run everything at once, you can get by like that.

Fine if you are running lights and heaters. Not so fine when starting motors.
That innocent looking freezer or fridge with a 4.0 amp nameplate draws 24 to 50 amps until it's up to speed.
Ever notice the lights dim when something starts up when on utility power? That's will several million HP on the far end of the power cord. A 7HP generator going to notice that motor load starting. Dropping frequency, dropping voltage and a few spike with some harmonics on the genset's output. The dirty power may affect some sensitive loads.
Would anybody here recommend running a generator with a nameplate capacity of 4000W continuously at 4000W?
Anytime and in particular at temps above 70F. Leave no less than a 10% margin instead of running on the ragged edge.
Have a look at the price of generators. The price between a too small 3500W and a barely large enough 6500W. It's only the price of a couple of restaurant meals and a 24 of beer.
It cost within pennies to run either genset down the production line, do the engineering, paperwork, shipping, insurance, wages etc. Going a few more bucks purchases a lot more generator.
If you are in this deep, may as well do it right.
Those LP Generac units even come with an automatic transfer panel. Pricing the 18KW auto start unit doesn't cost any more than a quality 6500W portable.
What are you doing about transfer switches? This post has been pretty quiet about that topic.
As for generators on the porch and extension cords run through doors or windows? They keep the fire department busy. Either putting the fires out. Or carrying the carbon monoxide victims outside to the ambulance.
Happens all the time. Even if the generator operator thinks to position the generator down wind of the house. The wind will shift and blow exhaust into the house.

Reminds me of the 2 painters by Shallow Lake North of Owen Sound that had the generator running while painting. They did not consider the "chimney effect" of the house.
Neither even made it out of the different rooms they were painting. I dont think they knew what hit them.

You can likely run about 17kw out of the tractor.. that's kinda an odd number.. I see 12/13/15/18kw units.. any would be acceptable... for your tractor..

soundguy

Also consider how much fuel to keep on hand.
When the power is out, the corner gas station
can't pump fuel if you run out.

Thanks for all the advice. I have found several used 15kw-25kw pto units for $1000-$1500. Figure on adding a manual transfer switch and power hook up next to the meter on the yard light pole. I"m sure that may be another $500-$1000..

So far a nice sized standby generator running off the LP tank is looking like a better option.

There sure are incredible LOW prices in your area.

An old military surplus unit if it says 10KW on the tag then rest assured it will do that all day and night. Mine was built in 1945 and has a Willys 4 cyl. Jeep engine. They don't build them like this anymore.

That water heater is a handicap for running on a generator. I have a 6k surge 5k running max that works well for me. Having an OHV engine makes a big difference in fuel usage. Diesel is even better. Whatever you do, be sure you have the high line disconnect. I back feed my entire place from a welder outlet in the shed where I can close the doors and leave the windows open for ventilation. Works fine. Just can't have everything on all the time. One more thing. Be sure you have a brushless generator head. Sensitive things like high efficiency furnaces don't always like the current produced by brush type generators.