Using portable generator to power furnace fan (AC/PSC motor) - yes or no?

Trader, some electronic controls NEED the neutral power line (white wire) to be at or near the same voltage as the safety ground (green wire) or else they will throw an error code.

If the neutral and ground are bonded together in the generator as they should be, it should work fine.

Mark

Some engineers are lazy, and the accountants win out - so the flame sensor only uses one wire, resorting to the "chassis ground" for return. If the chassis ground and the neutral are at different potential, the controller mis-reads the sensor foltage and determines that the flame has gone out - so it shuts off the gas and the flame DOES go out.

I agree. But that doesn't sound like what Danny was talking about, he was pointing the finger at flames sensors. A code for an incoming power problem would set a different code. But then the whole thing was vague, so who knows. I also later posted that I don't see how the flame sensor would be sensitive to any of this, because they are on the DC side of the power, a rod type would rely on detecting a very small voltage between the rod and metal frame of the furnace on the DC side and I don't see how that could be affected by a generator. Also there sure a lot of people using generators with furnaces and this is the first I've ever heard of anything like this. So Fretwell maybe right, anecdotal, second had reports from one HVAC guy, who knows what was really going on.

As to the neutral and ground being bonded together in the generator, that's only correct if you're using extension cords. If the generator is wired into the panel, then unless the neutral is also switched, which few are, the neutral at the generator is not to be bonded to ground there, if you follow code. Also, from what I can gather, most generators have the neutral and ground bonded from the factory, but some do not. And if you have one that is bonded and it includes GFCI on the main output that you're connecting to the house panel, then unless you have a switched neutral at the panel, the GFCI will trip as soon as it's connected and turned on. Some people have their generators set up with the neutral and ground not bonded and then use a shorting plug that makes that connection when using the generator as a portable.

The flame sensor is with the electronics, on the DC side, and one would expect that the DC side would be tied to ground via the metal frame of the furnace. It has to be to complete a circuit for the flame sensor to work. So, I'm not seeing how a difference in potential between the neutral and ground would be an issue. For that matter, there is typically a varying difference in voltage between them all the time. It will depend on the current flow in the neutral, which changes. So, if the furnace is sensitive to that, why doesn't it trip frequently on line power too?

Danny, in his original comment, emphasized he was quoting from one of the local HVAC installers (a legitimately highly regarded group) regarding problems with standby generators and heating systems, and didn't have direct, first hand, experience.