Is it alright to run furnace and turn off gas?

Question

Is running a furnace with the gas pipe shut can cause any harm to furnace?

Answer 1

I presume you want to do this just to circulate air? Do you have a thermostat connected to the furnace? If you do, you might have an option to turn the blower on manually.

If so, you could set the system "off" (cooling, heating, off), then turn on the blower and let it run without worrying about the furnace continually triggering the igniter or locking out. Or maybe you can put your thermostat in "heat" mode, turn the setting up higher than the actual temperature and turn the blower on. The blower will run, but the furnace won't try to ignite and it won't matter whether the gas is turned on or off.

For example, the Honeywell thermostat pictured below lets you turn the blower on whether the thermostat of set for Heat, Off or Cool.

Answer 2

It might cause harm if the furnace were trying to ignite in which case the igniter will die prematurely.

If only the furnace air handler blower is running, having the fuel off is completely fine.

Answer 3

No, it should cause no damage at all. However, if the unit is switched into heating mode, it could (should) eventually go into lockout. At which time you'd have to follow the procedure to get the unit out of lockout, which varies from unit to unit.

If you're looking to circulate air, turn the FAN setting on the thermostat from AUTO to ON. This will turn the blower on, without activating the heating or cooling function.

If you want to run the unit in cooling mode, just set the thermostat to COOL. This will turn the blower on/off with the A/C unit.

Both these modes should function properly with the gas off, and no damage will be caused to the system by having the gas off.

Answer 4

Doing this with my system (York ~2002) will blow a fuse, probably because the igniter keeps trying to light a nonexistent gas flow. Your mileage may vary.