How big of a generator do I need?

I am wanting to purchase a generator big enough to run my entire house and barns. In the barns I only have 120 volt lights that I can shut off all but 1 if needed. In my house everything is electric except the furnance. I have a gas stove hooked up in the basement to use in emergencies so I wouldnt have to use the electric stove. I have a deep freeze. I wanna get this purchased before this winter. I am thinking a 8000 watt but thats only a guess! How big do you think? Thanks for your help.

Turn on what you want to run on generator, then get an electrician
to put a current probe on the lines and see what you are drawing. A
rule of thumb is 8 amps per KW at 120V.

I would think you would be looking at 15-20 KW minimum.

You also have to consider if there are any motors that need to start up as they require more amps at start up.

Depends on what you want to run and how much 'load management' you want to do. As someone suggested... turn on the things you want to run and monitor each leg of the mains for a while with a current clamp and see what it's drawing while things cycle. I think you'll find that to have some comfort with starting loads on things like pumps and compressors you'll want about 40 amps available. Keeping in mind that most gens are rated at 250 volts... that equates to 10 KVA or 10,000 watts.
We have a 6500 watt here that makes 20 amps. It's not nearly enough. Power was off last night and today... so I hauled out the 25 kva we have for the farm (after the little one wouldn't run anyway). It was easier to hook the Magnate to the tractor than screw with a chink carb.
You might want to think about that too and just get a 25 kva PTO gen.

Rod

Don't forget the water pump, electric water heater, etc. These loads can be managed by turning off the water heater when you're using the electric range for instance.

How much fuel do you normally have at your disposal? I can get 14 hours out of four gallons of gasoline if I manage my loads properly. No TV, computer, or other luxuries. Only the deepfreezes, refrig's, the heat plant, and the deep well. After all, it is an emergency generator.

I'd seriously think about a propane unit if I really wanted to run everything during a power failure. My boss had a nice one installed for his invalid mother. It would automatically start once a week and run an auto-diagnostic check, charge the starting battery, and shut off. When the power blinked, it was up and running before the lights went completely out.

A pricey system, but if you really need it. . .

She was medically dependant on it.

Paul

Wav(e) formula....watts equals amps times volts. Do the math....look at what you really need to run...each appliance, pump, heater, cooler, etc. Need to allow some extras for startup, especially on the bigger users.

Well go look in your breaker box. Then figure if you have a 200 amp service at 240 volts then how big do you need. Then figure from there you need double that to do the job 100% I know the 6.5 KW one I have will not even come close to running my house

If I was you get home standby generator that will supply 70 amps or so of power. That would be about a 15 kilowatt unit. A home standby generator that size is about $4,000 + transfer switch + install.

If you want to be running extension cords all over then you can spend $1,000 and get a 7500 watt portable generator. I have a 10HP 5500 watt portable Coleman with a Subaru engine, it gets me by.

If you don't run air conditioning or your electric range, a 5000 watt unit should suffice. If you expect to run central air, you'll want at least a 6500 watt unit.

Note that air conditioning and refrigeration have high starting loads. You can get by with an undersized generator if you don't try to start your refrigerator, freezer and A/C at the same time.

As some have suggested your willingness to manage loads plays a large role in sizing as does what you deem essential. As an example my in-laws down the road have basically the same amount of electrical apparatus around the home as I do with the exception I have a well pump and they are on city water. Wife and I got along for 10 years with a 3500 watt portable while the in-laws struggle to get along with 3 times that much capacity, why? Becuase they refuse to manage their usage. We have since up graded to a much larger diesel powered unit, not out of need, but purely out of “want”.

Unless you are technicaly capable. The system has to be fool proof so the rest of the family doesn't trip or burn out the generator.
As for running extension cords through doors and windows? Works well to thin out the shallow end of the gene pool. The cords are usually plenty short requiring the generator to be place dclose to the opening. Later the wind shifts and CO from the exhaust enters the home and puts the occupants into thier last sleep.
A 6500W generator can be tripped with a mere 4000W load if the loads are not balanced.
Too many poeple are so prouid of "making do", "getting by" and are proud of suffering and proud of being humble.
Purchase enough generator to run the well pump, furnace fan, sump pump, fridge, freezer and the lights. Then allow enough capacity to start motor loads without having to unplug other loads. And be done with it.
Does anybody really thing a 3500W generator should be operated at 3500W continious?
The

Justin:
You’ve got a lot of good information here. Buickanddeere, in particular, offers good advice. Most folks can “Get by” with a 5000 to 6500 watt generator, if used properly. Now, here’s the BUT....Be careful the load, the location, the extension cord capacity and gasoline storage. AND don’t use it where fumes can enter occupied area of the dwelling.
That being said, If your budget will handle it, a propane powered standby generator in the 15kw range (+/-) is probably the best bet. Propane doesn’t gel and is safe to store. Starts automatically and exercises on a scheduled basis. Good luck....keep us posted.

Jake 2

A few years ago I picked up an 18KW Onan on ebay for
$2000 plus $500 shipping. The seller set it for
single phase and propane before shipping and I wired
it up to a whole house transfer switch when it
arrived.

My total cost was about $3000 and it runs everything
with ease. It would be hard to find a cheaper way
to set up a standby system, and there is no need to
worry about balancing the load.

Oh yeah....PLEASE don't even consider "Backfeeding" through a garage, barn or other building. Use a transfer switch.

Jake 2

Best way. Take an amp reading of your house. As others have posted. Then add a little to that for equipment starting. What ever you do. Stay away from Generac. You can get them cheap but parts cost are very high,not dependable,hard to find anyone to work on them. Factory support is very poor. Go with a name brand unit.


Onan tech since 1980.

Excellent point

http://www.reliancecontrols.com/ProductDetail.aspx?TWB2012DR

That formula works with heaters and incandescent lamps. However the watts a motor uses and the Volts X Amps a motor draws is another issue.
Happens all the time a 1500W supply trips off on overload because aload with 1800-2000VA/1500watt demand has been placed on it.

I can get by with a 4000 watt, for emergencies. That said, we are able to manage our loads, rotating thru refrigeration, water, and heat, or window air, if needed. Key is to manage loads, cut your life style to only what is absolutely necessary. When a second 5000 wat came my way, I figured I had the hog by the tail. If you need to run the whole farmstead, feeders, continuous waters, milk coolers, then you'd better get the pprofessional in. without overview of the situation, none of us can readily advise you. One other thing to think about is fuel source, and bigger generators use more fuel. None of them are fuel efficient - they're all stopgap measures. How many 5 gallon cans can you safely store? Do you have a bulk tank? Will you be able to get fuel when neighborhood is without power? With the new computer operated pumps, your local gas station may be out of luck.

Good post Ray. The reality is: The last couple of major outages that we had, there were lots of big generators, but a five gallon can of fuel didn't last long. A person really needs a hundred gallons of fuel to start with, and that may not be enough in a real crisis. I really think the grid will fail sometime in my lifetime. Then we'll need shotgun shells in addition to the gasoline. Trouble is, I don't think I'm mentally equipped to deny a hungry family.

There's lots of big headed people running our electrical system.

Pride goeth before the fall. . .

Paul

After messing with the portables and trying to keep gas in them
and shuffling usage, I went with a 15 kw with an automatic
transfer switch power by LP gas. I have a 500 gallon tank on
the house. It runs everything and I have no change in
lifestyle other that all the extra folks that seem to show up
when they figure out I still have AC. I'm in Houston and have
been through a few hurricanes.

"5 gallons of gas doesn’t last long"

Heck just order up an 8000 gallon transport load it means nothing when you want juice correct? and besides your only talking about 32 grande?

Fuel type, usage and cost are things that anyone outside of the wealthy should consider when choosing a home generator. 1 gallon per hour, from what I hear is not uncommon with a larger gasoline powered generator units. The last trip I made to the gas station means that usage equates to $100 for one day’s worth of power or $700 for a weeks worth. People who have purchased and are now stuck with a big generator also find out that cutting usage in half doesn't mean fuel usage is cut same amount. Diesel power helps out in that respect being as they are more efficient at partial loads than spark ignition engines but bigger takes more fuel to do light work no matter the fuel.

A few of the questions that one should consider are; How often does your power go off? For how long? Likelihood of long term outages? How much is whole house comfort on genny power going to cost both per day and week? How are you going to store fuel? How are you going to acquire fuel if the grid is down for say a week? What is the largest single load that you want (or need) to start and run? How much can I afford to purchase, install correctly, and operate?

As stated earier we got along just fine for years with 3500 watt (for the ankle biter that is 3500 continuous and 5000 peek) Now that I am a bit more financialy capible I have two diesel sets that I put together in the shop. One that will run the whole house and shop in total comfort and one for the long haul and over night that will run on less than a quart per hour. They serve me well in my personal situation.

"5 gallons of gas doesn’t last long"
Heck just order up an 8000 gallon transport load it means nothing when you want juice correct? and besides your only talking about 32 grand?

Fuel type, usage and cost are things that anyone outside of the wealthy

Are wealthy people bad people?


should consider when choosing a home generator. 1 gallon per hour, from what I hear is not uncommon with a larger gasoline powered generator units. The last trip I made to the gas station means that usage equates to $100 for one day’s worth of power or $700 for a weeks worth. People who have purchased and are now stuck with a big generator also find out that cutting usage in half doesn't mean fuel usage is cut same amount. Diesel power helps out in that respect being as they are more efficient at partial loads than spark ignition engines but bigger takes more fuel to do light work no matter the fuel.

A gallon of gasoline per hour for a generator? That would run a 10,000W unit under full load. That is a lot of power to draw continuous overnight for just a home. 10KW would carry many farms except during milking or while grinding feed.

Running a generator to power an electric water heater or electric resistance heating for general building occupation is inefficient. A kerosene heater would serve better.

A few of the questions that one should consider are; How often does your power go off? For how long? Likelihood of long term outages? How much is whole house comfort on generator power going to cost both per day and week? How are you going to store fuel? How are you going to acquire fuel if the grid is down for say a week? What is the largest single load that you want (or need) to start and run? How much can I afford to purchase, install correctly, and operate?

In most circumstances power is off for less than 48hr in an area. Of course some low population density rural areas are the last to be restored so 3 to 7 days outages occasionally occur. However the local towns will be powered up and fuel will be available in a couple of days.

As stated earlier we got along just fine for years with 3500 watt (for the ankle biter that is 3500 continuous and 5000 peak) Now that I am a bit more financially capable I have two diesel sets that I put together in the shop. One that will run the whole house and shop in total comfort and one for the long haul and over night that will run on less than a quart per hour. They serve me well in my personal situation.

Fixed up most of the grammar and spelling errors for you.

As for generator size. If it takes a 6.5 KW unit to start a 1HP deep well pump that only draws 1.5KVA when running. Then that is the bottom end size gen set required.

For the average Joe, going up a size or two larger that the absolute minimum. Will save many baffled and frustrated moments in the dark.

I have a 5K continuous portable. I power the whole house with it. Not enough to run the A/C, but plenty to keep the fridge, freezer, and a few lights on. The furnace, stove, and water heater are gas. I've never had to use it in the summer, but there were a few ice storms and it used about 7 gallons of gas in 24hrs. (OHV engine)

Back in 2008 during our big ice storm my wife and I survived just fine with no generator at all. In '98 my folks and I survived 69 hours in a bad ice storm with no generator at all.
In both cases we had heat, my folks burn coal, we've have wood. We had food, my folks have a gas range, I have a Coleman stove.
In 2008 we did better because my 400w inverter and motorcycle battery would run my laptop and a couple lights. We had internet access too.

My buddy ran his generator 24x7. He was worried his freezer would warm up. My wife's grandparent's lost a freezer worth of food.

I froze a couple gallon milk bottles outside (ice storm remember), with some salt added (which lowers them well below 32F) they kept our fridge plenty cold...

Besides which if you keep the door closed your freezer will stay cold for days.

"Fixed up most of the grammar and spelling errors for you."

Wow, just, wow...



Uncalled for, unpleasant, unacceptable, childish.

You forgot to include "(for the ankle biter that is 3500 continuous and 5000 peek)".