Heating & Air Conditioning Electrical Wiring

Running a furnace using a generator?

5 years ago

last modified: 5 years ago

Hello, my question is the house we bought has a plug coming off the circuit breaker that is a 30amp plug to go into a generator in case of a power outage. We just bought a 9,500 running wattage generator in case of power outage this winter. The generator has a 50amp plug in and a 30amp plug in. With the current set up of the 30amp plug coming out of the circuit breaker, would this be enough to connect to our generator and run our furnace in the winter if their is an outage? We have a geothermal system for heating and cooling if that helps. And should I pay to have the 30amp changed out for a 50amp since the generator we have does do 50amp service as well? Is there any benefit to that?

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fsq4cw

5 years ago

last modified: 5 years ago

Let’s decode your HP’s essential info.

All the info for the generator capacity is contained within the ‘Boiler Plate’ pic of this heat pump that happens to be a Geostar MagnoliaPlus 5-ton geothermal. If your unit does not have an ‘Intellistart’ soft start kit option, you might need a 45-50kW generator. If your HP has ‘Intellistart’ you can use a 16-kW generator. You will have to verify what options your HP has. Your model number indicates that this unit does NOT have the ‘Intellistart’ option factory installed according to the model number; perhaps your dealer installed it afterwards, check your contract and service records.

The other essential info that is on the sticker photo you posted is ‘Compressor LRA’ with the asterisk beside 152.9(amps). Now follow that asterisk down to where it appears again in the sticker’s ‘Comments’ that says:

“WITH INTELLISTART LRA=54.0” (meaning 54.0-amps).

LRA stands for ‘Locked Rotor Amps’ of the compressor motor’s rotor shaft while drawing its maximum in-rush current during startup. These are hard numbers. You need a generator that has this capacity and a power reserve beyond this number to have a margin of reserve generating capacity to start this compressor. There are other components too that have to be considered as well, the computer, thermostat, blower motor, desuperheater pump motor, flow centre pump motors (you should have-2). All this has to be added to the generator’s capacity. This is the bad news.

Now that you (hopefully) understand the explanation of why you need a monster generator, here’s the good news because the good news is practical info that you can take to the bank. Forget EVERYTHING you’ve read in this thread up till now; it mostly background noise as relating to ‘capacity’.

Your HP is probably equipped with backup heat strips (resistance heating elements), hopefully staged. Should you have an extended power outage, my ‘practical’ recommendation would be to set up a ‘modest', affordable generator, set your geothermal heat pump to ‘Emergency Heat’ (once connected). That would essentially bypass all of the HP except for the controls, blower motor and backup heat strips that are hopefully staged.

If you can’t live without air-conditioning for a few hours or even a few days, get a window air-conditioner and try living in a smaller area of your home. If you want the whole enchilada and have a medical condition requiring serious power - Get a Diesel ‘Cat’!

IMPO

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Comments (13)

kudzu9
5 years ago
Two questions:

1. What are the power requirements listed on the nameplate of your furnace/geothermal system?

2. Do you have a transfer switch installed?
Auggie's Life
Original Author
5 years ago
1.) I’ve attached a picture of the name plate as I’m not sure what I am looking for.

2.) As far as the transfer switch goes and what I’ve read online about them, it does not look like it. It looks like its connected to a 30amp breaker in the circuit box. I could be wrong about the transfer switch but there is not a seperate box and breakers.
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Seabornman
5 years ago
What size breaker is system on now? Do you also have a backup resistance heat coil (it may have its own breaker).
Auggie's Life
Original Author
5 years ago
Thank you for the responses, how would I figure that information out? If I think I understand what you are asking and go over to the circuit panel and look to see where the furnace is connected, it has 6- 60amp breakers on the circuit panel that say “Furnace”. There is no Breaker that says anything related to a heat coil
Ron Natalie
5 years ago
Nope, it isn't going to work. Even the continuous rating on the thing is going to be right at the threshold of that generator's capacity. The compressor will draw way more than the capacity when it starts. And that doesn't even take into account anything else you might have running while on the generator.

And if all you have is a backfed 30A breaker, it's not even going to come close. Also, just a breaker (without interlock) is ILLEGAL AND UNSAFE.
Seabornman
5 years ago
So those breakers are tandem breakers, meaning two breakers get flipped with one handle? It really is immaterial, as any one of those loads exceeds your generator capacity.
mike_home
5 years ago
The sticker says the minimum circuit amperage is 47.2 A with a 208/230 V service and the none of the heater's is checked off. A 50 amp breaker is likely to trip on start up. You need a 60 amp breaker connected to 220 V. Even if your 9500 W generator had a 220 V outlet, it can't supply the required current.

You also need to power the thermostat. The thermostat is usually on a separate 120 V circuit which powers a 24 V transformer. There may be other 120 V or 220 V circuits associated with your geothermal system. You would need to isolate all of them if you are going to power them with a generator. Are the 6 breakers labeled furnace all connected as 220 V circuits? That would mean there a 3 circuits each having a breaker on each of the 120 V legs.

My advice would be to have an electrician determine what is required and install the proper transfer switch. You need a properly sized generator. If the goal is to heat the house when the power fails, then you need to think about how the transfer switch will operate when you are not not home during a power outage.
Auggie's Life
Original Author
5 years ago
This was all very helpful, thank you very much for the responses
kudzu9
5 years ago
And regardless of what you decide to do, please don’t ever have the generator connected to that panel without a properly installed transfer switch.
sktn77a
5 years ago
Well, you don't have a "furnace", you basically have a heatpump (geothermal). So the current requirements are much higher than a typical furnace. You might get by with 50 amps if your setup permits this. I don't know if your generator supports anything higher. Call the manufacturer (or installer) to find out.
Auggie's Life
Original Author
5 years ago
I will look into getting the transfer switch before I do anything. Thank you for the help again
PRO
Berkshire Electric
3 years ago
last modified: 3 years ago
Licensed electrician . 25 years in biz. Listen to this guy right here.