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doechsli 12-05-2013 10:50 AM

Running a gas furnace off a generator....
Not sure if this is the proper forum or not......

There seems to be so much conflicting information on how to make this work. From what I have read, many furnaces will not operate off of a generator. I have read the cause is anything from a bad ground to "dirty" power produced by the generator. Is there any rules of thumb as to how to buy/connect a generator to drive a typical natural gas furnace? The only real load would seem to be the blower and that would not seem to require a large/expensive generator.

As a follow up question, a saw setup for wiring a furnace to run off a generator that seemed safe and inexpensive. There was a "pig tail" wired into the power supply of the furnace with a typical three prong male plug. Attached to the conduit was a three prong outlet coming from the breaker box. Under normal circumstances the plug is connected to the outlet. In an emergency, the furnace is connected to a properly sized extension out to the generator. Safe or not?

Blue Jay 12-05-2013 03:11 PM

Yes that would be the safe way to do it. Now if your generator has a very noisy output (ie AC not sound) it might be a problem. Hook it up and try it out before you need it for real.

kok328 12-05-2013 03:40 PM

It is my understanding that generators without a pure sine wave are extremely hard on motors and you run the risk of burning up the motor. I imagine printed circuit boards (PCB's) are voltage sensitive too.

bud16415 12-06-2013 05:19 AM

I have been hearing good things about the Honda units that are inverter stabilized. I’m sure there are many others. My electronics I power thru a battery backup inverter system that’s always connected to line feed. I think these inverter stabilized units work much the same way, only have a gas engine and alternator / generator all in one unit. Most electronics I think converts to DC first thing and in doing so cleans up the power to circuit cards and such. I would still look for a unit that talked about stabilized power and showed some examples of expected wave form. You could always put a scope on the line also to get a feel for how clean the output is if you have one.

Here is a link to the Honda site as an example.

bud16415 12-06-2013 05:52 AM

PS: Your method of switching and isolating the furnace sounds fine to me and what I would likely do if I wanted a simple method of just keeping the heat on. I would also add a switch after the plug I think maybe a fuse also. I would want to have the gen running smoothly be able to look at the output on its display if it had one then plug in the extension cord making a good connection and then flip the switch to power up the furnace. I would also want at minimum a couple other things powered in an emergency even if it was just a light near the furnace could come off the switch box. I would want a light in the kitchen power to the fridge and maybe the microwave and an outlet for a little tv or radio etc.

I sat out a 7 day power outage in the winter after a blizzard once being unprepared and scrambling around making makeshift heating sources etc. The time to plan is in advance. And those few simple comfort items make a world of difference.

The new old place we just bought has no backup at this point and over Thanksgiving our furnace died the holiday coincided with buck hunting and I couldn’t find a heat guy to come out right away. The house had a doorway between the kitchen and the rest of the house and in the attic I found the old door and rehung it after 50 years up there. Everyone told me there was no need for a door there and I agreed but hung it anyway. Well with the furnace out and a foot of snow outside and temp in the low 20’s, I shut the door turned on two burners on the gas stove top and stayed nice and warm for 12 hours till the furnace was repaired. The rest of the house got down to around 40. Far from a perfect backup plan but better than nothing.

The whole house systems are great and also out of a lot of people’s price range. A small unit sitting in the garage can help a lot and can come in handy for other things as well. It’s a good idea to run them a few times a year anyway.

Blue Jay 12-06-2013 07:20 PM


Originally Posted by kok328 (Post 96875)
It is my understanding that generators without a pure sine wave are extremely hard on motors and you run the risk of burning up the motor. I imagine printed circuit boards (PCB's) are voltage sensitive too.

I have an older Coleman PowerMate 4K that serves me well with no trouble, not a pure sine wave but still clean AC. Ran it straight for 6 days keeping furnace, sump pump, deep freeze, refrigerator and well pump on line, just did not have all on at the same time.

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