Help sizing a generator for home backup?

[adettman]

Hi, folks. Does anyone have any insights regarding sizing a portable generator for home backup? My electrician is prepared to set me up with a (legitimate, up-to-code) method for backfeeding my panel in the case of a power outage. I'm barely a novice in terms of electrical work/home wiring and so please don't ask me to provide details regarding his methods or materials.. just know that he is a licensed electrician!

That being said, any recommendations regarding what'd be an adequately sized portable generator to provide backup power for my home? In terms of usage/load, my goal would be to maintain power to the pumps/computer associated with my propane boiler (home heat + hot water), well pump, freezers (one chest, one upright), refrigerator, air exchange system, and then I guess some lights and probably a laptop/phone charger. I don't own air conditioners nor would I plan on running power tools during a power outage. Additionally, I think I could handle the responsibility/"burden" of unplugging my freezers once they got to temp (just meaning that some stuff wouldn't have to stay plugged in/operational constantly). My primary concern would be to keep my boiler functioning (as this will provide my home heat in addition to my woodstove) and my well pump operational.. as well as my fridge and some lights I suppose.

In light of all this, would a 4,000W generator suffice? Or is that cutting it close? Is something like 6,500W more appropriate? [LAST MINUTE EDIT BEFORE BED: Upon some more investigating, sure seems like 6500W is more appropriate in my case. I have yet to dig out the literature on my well pump but was unaware that those were such a heavy draw. Sounds like a 4000W generator would likely handle a well pump just fine but then maybe not much more..? Any thoughts?]

I should also mention (perhaps very important) that my power doesn't go out very regularly. Furthermore, if and when it does go out it rarely lasts more than a few hours. And again, this is perhaps twice a year. I just happen to live in a very cold part of the country (Northern Minnesota) and a modestly priced generator seems like reasonable "insurance" against frozen pipes!

Thanks for your time..

 

[CobyRupert]

You’ve made a pretty good list of the loads you expect to run on the generator. Next step is to add up their wattages.

 

[BrokenTrack]

Usually with a generator, you run out of amps before you run out of wattage.

For instance my generator is a PTO Generator (runs off my tractor) and so it is a 83 amp/20,000 watt generator.

Since a home can generally be run with little worry about shutting this off, or that off at 10,000 watts, I could almost run (2) houses watt wise, but the amps is the limiting factor. To reword that, can you imagine what people would say if I said, "I only have an 80 amp service to my home" when most homes today have 200 amp service? But that is what I have when I am operating by my generator; 80 amps.

If you are on here, I assume you have a tractor. I really like PTO generators because they have clean power unlike portable generators, and since you are not buying an engine, for the money you can get a lot of back-up power for very little money. And there are a lot of rebuilt pto generators (used generators) that would net you three times the power, for the same money as a new portable generator.

The downside is, you are using your tractor so you are putting hours on it just making juice for the family, and sometimes you want to use the tractor at the same time the family wants to watch TV. But I do not find it to be too bad. The family can go without power for the hour it takes to plow my driveway of snow for instance, and I did buy my tractor to use, so what is 18 extra hours on it when my family is happy with power in the house?

And with PTO generators you get a lot better power as it is clean power (safe for electronics) and the tractor can regulate loading better since it has more turning mass, and a better generator like when the water pump snaps on. And a person tends to have plenty of fuel on hand for the tractor, and the fact that it always starts because portable generators can varnish the gasoline if not run now and then. Since most people use their tractors a lot, they always start.

I like PTO generators. When lit, my family cannot tell the difference between grid power and back-up power; which really says a lot.

 

[RandyT]

Need to look up all the running watts of everything that you plan on running at the same time. then add the starting wattage of the largest thing on the list which is most likely the well pump.and then add about 20% to that number and then get the generator with at least that but would recommend more watts than your list showed.

 

[seville009]

Lots of generator sizing websites to assist you - here’s one random site

Norwall Power Expert—Sizing Calculators and Selection Guides

 

[defranks]

Usually with a generator, you run out of amps before you run out of wattage.

For instance my generator is a PTO Generator (runs off my tractor) and so it is a 83 amp/20,000 watt generator.

Since a home can generally be run with little worry about shutting this off, or that off at 10,000 watts, I could almost run (2) houses watt wise, but the amps is the limiting factor. To reword that, can you imagine what people would say if I said, "I only have an 80 amp service to my home" when most homes today have 200 amp service? But that is what I have when I am operating by my generator; 80 amps.

If you are on here, I assume you have a tractor. I really like PTO generators because they have clean power unlike portable generators, and since you are not buying an engine, for the money you can get a lot of back-up power for very little money. And there are a lot of rebuilt pto generators (used generators) that would net you three times the power, for the same money as a new portable generator.

The downside is, you are using your tractor so you are putting hours on it just making juice for the family, and sometimes you want to use the tractor at the same time the family wants to watch TV. But I do not find it to be too bad. The family can go without power for the hour it takes to plow my driveway of snow for instance, and I did buy my tractor to use, so what is 18 extra hours on it when my family is happy with power in the house?

And with PTO generators you get a lot better power as it is clean power (safe for electronics) and the tractor can regulate loading better since it has more turning mass, and a better generator like when the water pump snaps on. And a person tends to have plenty of fuel on hand for the tractor, and the fact that it always starts because portable generators can varnish the gasoline if not run now and then. Since most people use their tractors a lot, they always start.

I like PTO generators. When lit, my family cannot tell the difference between grid power and back-up power; which really says a lot.

Broken Track is missing that current (amps) and power (watts) are co-dependent. The basic formula is power = voltage times current, P=IxE. Your voltage won't change at 230V (two 115v phases) so current and watts will track one another. So consider your load, as others have mentioned, and calculate wattage. Bear in mind that things with motors, your well for example, will require a higher start-up current than it will use while running.

 

[TnAndy]

Something else you might factor in.....the type of fuel. Given you only plan to use this occasionally, you might consider a propane or natural gas fueled unit. Gasoline units tend to be way less forgiving about storage for long periods without use.

 

[seville009]

Also - as with almost any equipment, it’s good to have too much capability as opposed to too little, so if it were me, get a generator that is larger than the max you think you'll need.

I had a “portable” 12,000 watt gas generator before I switched to a whole house 18,000 watt propane stand by generator. The 12,000 watt ran great with everything running; no real hiccups when the furnace or water pump kicked on.

 

[Carl_NH]

.

In light of all this, would a 4,000W generator suffice? Or is that cutting it close? Is something like 6,500W more appropriate? [LAST MINUTE EDIT BEFORE BED: Upon some more investigating, sure seems like 6500W is more appropriate in my case. I have yet to dig out the literature on my well pump but was unaware that those were such a heavy draw. Sounds like a 4000W generator would likely handle a well pump just fine but then maybe not much more..? Any thoughts?]
I
Thanks for your time..

We have the same setup, an oil boiler for DHW and heat and a fridge and lights/tv, but the biggest draw is the 1.5 HP well pump 20 amps starting amps 13 running so we have a 7500W generator with 32 amps @ 240 volts and 9000W starting. It runs everything fine, but we limit the water usage and have a 26 gallon drawdown (two tanks) so it runs maybe 2-3 times in a typical outage of a day, as we limit water use to minimize pump starts.

So depending on your pump size then the rest of the load, I would consider a 8000 or 9000 W running generator.

 

[YanmarFever]

We have the same setup, an oil boiler for DHW and heat and a fridge and lights/tv, but the biggest draw is the 1.5 HP well pump 20 amps starting amps 13 running so we have a 7500W generator with 32 amps @ 240 volts and 9000W starting. It runs everything fine, but we limit the water usage and have a 26 gallon drawdown (two tanks) so it runs maybe 2-3 times in a typical outage of a day, as we limit water use to minimize pump starts.

So depending on your pump size then the rest of the load, I would consider a 8000 or 9000 W running generator.

This apply's to tractors and generators.
Find the one that you want, then buy the next size up.