Is it Safe to Run a Furnace on an Inverter? (2023 Update)

[Chet Kincaid]

About a 25 year old forced air gas furnace, the kind with an inducer blower. No fancy electronics; just whatever kind of time delay they have for the blower and an updated inducer control board also has a delay circuit. So it's more a matter of wondering if the motors, gas valve, and transformer will object to the perverted waveform of a "simulated sine wave" inverter. I have a real generator so the inverter is more of a backup to a backup. Thought I'd ask first.

I'm going to guess that the 24V transformer will have an output that's closer to a real sine wave which lessens any unhappiness of the gas valve and electronics so I suppose the transformer itself and the motors are the items of concern.

[Pete C.]

Motors and solenoid valves are the least likely components to care about the AC waveform. Both motors and solenoid valves are routinely operated with PWM type drivers which produce waveforms much further from a sine wave than a "MSW" stepped square wave inverter. As long as the inverter is appropriately sized it should be fine.

[Chet Kincaid]

Routinely? On a simple furnace that's 25 years old? Rest assured the motors run directly on line power and the electronics such as there are on

24 V from a transformer.

2500 continuous, 5kW surge.

[Pete C.]

You missed my point. I didn't say the motors or solenoid valves in your furnace ran on PWM drives, I noted that motors and solenoid valves in general are routinely operated on PWM drives. The motors and solenoid valves in your furnace should be quite happy on MSW power.

That should be plenty for a residential sized furnace. You of course need a hefty DC supply to power that inverter, presumably a vehicle alternator. That will likely draw around 100A DC running the furnace.

[hrhofmann]

Do you mean inverter that runs from a dc source and generates ac, or do you mean a generator that runs from a gasoline-driven motor? A

2500 watt inverter would require humongous sized feeder cables if it runs on 12V dc.

[ransley]

Not only big cables, but I saw reviews of several 12v cheapy inverters, none could supply the rated watts, they were 10-15% off. So if you have a 1000w inverter unit it may shut down as a 350w motor pushes through its 850w needed startup surge. A 25 yr old furnace, its motor is worn and could take well over 1200 startup surge, so a 2000w inverter might work.

[Chet Kincaid]

Ah, I see what you mean. Thanks.

[Chet Kincaid]

It's a Cobra CPI-2550 rated at 2500 W / 5000 W surge. (In the manual they admit that 2500 is a one hour rating). I've tested it to about 1900 W with resistive loads and some smaller inductive loads. (Meaning I plugged in an air compressor because it was handy. It ran okay.)

I will likely never use it for the furnace since I have a generator but it's good to have options.

[365pete]

i have a new trane hvac and i bought a 24v msw inverter with 3000/6000 watt rating...it has a wi-fi thermostat, and i could use some assurance that a msw won't mess up a honeywell wi-fi thermostat, before i try it [only for gas heat]...i'm using large deep charge batteries (in series) from a q6 power wheelchair which are rated at 100 Ah each... i'll just use it if power co. rotates our power off every six hours, again, here in another unusual texas winter ...thanks ahead for any advise !

[micky]

Write to Trane. Save their printed answer in case you have a warranty claim.

[Clare Snyder]

It is definitely safe to ruin on a true sine wave inverter.Trying to run on a MSW inverter is a crap shoot at best.