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Posted: 10/26/2010 7:08:14 AM EDT
Is it possible to figure out what size of generator I would need to run a heat pump w/ electric backup, a fridge, 5ft chest freezer, and a 50 gallon water heater?  Also I have a 200amp main breaker box in my house and would assume I would want it wired in so I could shut off the circuit to the outside world as well if I needed to use it.

Thanks
Link Posted: 10/26/2010 7:11:17 AM EDT
Add up all the peak watt usage for everything.
Link Posted: 10/26/2010 8:39:30 AM EDT
[Last Edit: 10/26/2010 8:40:23 AM EDT by ColtRifle]
Originally Posted By jlficken:
Is it possible to figure out what size of generator I would need to run a heat pump w/ electric backup, a fridge, 5ft chest freezer, and a 50 gallon water heater?  Also I have a 200amp main breaker box in my house and would assume I would want it wired in so I could shut off the circuit to the outside world as well if I needed to use it.

Thanks




Without knowing for certain, I would suspect that you would need about 20-25 kw capacity.  That's a big generator and will use a LOT of fuel.  

You will need a transfer switch and a means of hooking up your generator.  With one of that size, you will quite likely have to hard wire it in.  

What you are wanting to do is gonna cost you BIG bucks.  Heat pumps and water heaters are big consumers of power.  The chest freezer and fridge won't use too much.  

I run my entire house (on city water so no well) on a 5500 watt running diesel generator.  That's an all electric house.  When the water heater is running (4500 watts) there isn't much capacity for much else.  However, once the water heater has heated the water up to temp, I can turn the water heater off and run pretty much everything else with the exception of the electric dryer and the heat pump.  We installed a pellet stove and that draws about 200 watts running so we can run it easily on a battery backup with inverter or on a small generator.  

I would look into an alternate heat source.  Put in a wood stove or a pellet stove and/or buy some backup heaters that run on kerosene and/or propane.  Forget the heat pump for backup power.  You will only use that much power when it's running and most of the time, it will just be consuming a LOT of fuel.
Link Posted: 10/26/2010 10:45:30 AM EDT
I have a 20kw whole house generator wired in with a automatic transfer switch. Water well, pool, septic system and all the house. Generator was 4k, propane hookup $600, electrical $1600. Have a 500 gallon propane tank. I would venture to say you need somewhere around a 12kw-17kw for what you want
Link Posted: 10/26/2010 11:35:31 AM EDT
[Last Edit: 10/26/2010 11:36:06 AM EDT by Hueto]
I power my entire house (about 2400 sq ft) through an auto transfer switch with a 14 kW... central a/c(forget the size, but it's a Lennox Infinity 17 or 21) , dehumidifier, 52 gal water heater, etc. Right now it's fed from a 250 gal propane tank. I can get about 4 or 5 days from an 80% tank charge. My inlaws have a slightly larger house with two a/c units. They went with a 20 kW with a 500 gallon tank, and we've run it for about 10 days without refilling.
Link Posted: 10/26/2010 12:02:39 PM EDT
I have a Kohler 30kw with an automatic transfer switch that runs on natty gas. About $12,000 all together. Very nice set up and will run my entire house including three heat pumps. The trick was getting the HVAC units to come on at thirty second intervals. This genset has a "once a week self test feature" which means that it comes on automatically and runs for 20 minutes so that the unit is "known" to be operational. The transfer switch DOES NOT come on during these test periods. I love it.

Just remember that you get what you pay for.
Link Posted: 10/26/2010 12:16:41 PM EDT
If you don't absolutely have to have an automatic failover and want to save yourself a  load of money check out the Cutler Hammer 200amp manual transfer switch. I picked one up at Harbor Freight of all places (its made in the USA).  It was something like $300. The automatic switches for 200A get really pricey. Over $1000 and even more if you need service disconnects in the switch. You can use the automatic switches with the individual circuits but I didn't want to have to pick and choose and really it would have been more work than just switching the entire load.

We have 300amp service coming in to the house so I was just going to power up our 200amp panel and move non-essential stuff to the 100amp panel. I have an old 16kw Generac unit and I knew it wouldnt power the whole load but since its a manual switch I can go out and shut off some circuits. We were total electric but since we had propane put in to run the generator we have switched our range top to propane. Everything else is AC.

The electrician who came out tested our load with both of our 3 ton ac units on along with 2 refrigerators a deep freeze a pool pump and whatever else was going on during a normal day with all the family home and we were only pulling something like 42amps. He said the switch was rated at 200amps continuous so basically if we turned on everything in the house we wouldn't be pulling over 200 amps so he just ran it all thru the switch. They fired up the generator and switched the load over and it almost started both AC units. It ran just fine with only 1 unit. They said that this older unit put out better power than the newer air cooled ones but still we would probably have to turn the breakers for one heat pump and both sets of aux heat strips if we were running the heat pump off the generator.

Having said all that a 16kw would probably run or come close to running everything minus say your stove and oven.
Link Posted: 10/26/2010 12:18:30 PM EDT
[Last Edit: 10/26/2010 12:20:11 PM EDT by ar-jedi]
first, get a tiny inverter-type generator, around 1.5KW to 2KW (see the Honda EU2000i as an example).  these types of generators sip fuel due to the intermediate stage of mechanical to electrical conversion –– and the result is that the engine only runs fast enough to power the load.  in contrast, a traditional mechanically coupled engine/generator setup requires the engine to always run at full speed (typically 3600 RPM, but 1800RPM for some larger systems) to maintain output voltage and frequency.  an inverter-type generator has no such limitation, and is far, far more fuel efficient with light loads than a large direct-coupled generator.  with a small inverter-type generator, you can power your fridge and possibly your chest freezer concurrently –– keeping your food stores intact.  this is the first step.  

for heat and larger current loads, you have to work out exactly where the BTUs/watts are going to come from.  as alluded to above, using wood as a backup for heat will be far less costly than purchasing a large enough generator to power the heat pump and electric heat system.  furthermore, you will need to store a lot of fuel (think: at least 100 gallons of diesel) to allow you to run a 20KW generator for a couple of days.  above 10KW output power, using propane or natural gas as a fuel will be more attractive, as these don't have spoilage limitations like gas and diesel.  nevertheless you have to bury a large propane tank or have a reliable supply of natural gas.

in summary:
(1) a small, lightweight, fuel-efficient generator for running your fridge/freezer for long periods of time.  
and possibly
(2) a larger generator which can be run intermittently for larger loads.

the approach i take is exactly as above, except in the case of (2) i use a PTO-driven generator hung off the three-point hitch of my Kubota tractor.  the last thing i need is yet another engine to maintain and service, and especially one which is used infrequently like a generator.  my tractor is dead-nuts reliable, i know it will run, and i always have fuel on hand for it which won't sit unused for months at a time.  for my intermittent need of high power (in my case it's a deep well pump, 240Vac at 30A), this is a perfect solution for me.

ar-jedi
Link Posted: 10/26/2010 12:21:42 PM EDT
Thanks for all of the replies.  I have done a little more research and it appears too that with being an all electric house it will cost big to put everything on it.


I have natural gas as an option if I get a meter back again but propane would probably be easier but I would have to buy a bigger tank.  

I do have a wood stove in the basement I just hate using it generally (too much work and I don't think it was installed properly and getting a draft is difficult/impossible sometimes.  I also see too many fires every year being on the local FD and don't know that it is worth it.  Also, without some kind of fan running I doubt much heat would make it up the stairs.  

I do have plenty of wood though just not the motivation to manage the stupid thing.  I either get it too hot, too cold, or don't get enough air too it or so it seems.  It's an old Federal Airtight and I guess I really don't know how to run it and have nobody to show me
Link Posted: 10/26/2010 12:38:19 PM EDT
I think a smaller generator first as well as some heavy duty extension cords are in order first then we will look into a bigger one.  I keep seeing $10k+ for one I would need and it just isn't feasible right now.

Thanks for all the help.


I also need to work on the wood stove some more.  I'm just a worrier by nature and can't sleep when the stove is running if I'm not watching it.
Link Posted: 10/26/2010 12:44:05 PM EDT
One more piece of advice- Whatever you go with, run the snot out of it for a week or two(changing oil and filters as needed though) to uncover any bugs or glitches. Both my Lennox and my FIL's Generac had teething issues. Mine had a problem with the trickle charge, and stopped having enough 12v power to run its weekly test cycle. We ran my FIL's house off of his for a week during construction so we could run the a/c units to acclimate his wood flooring before installation. It died do to battery failure twice. Better to test them whe you can afford to not need them.
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