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Question: Can I wire my gas furnace up to run off a generator in an emergency situation?

generator with power cord

Question: Can I wire my gas furnace up to run off a generator in an emergency situation? My home and family need heat! It is below zero outside!

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Answer:  We have this question asked quite often since we are in the wintertime ice storm season! The answer is, “Yes!” You can run your gas furnace off of a generator to get the heat for your family and for your home! I have hooked our generator up to our Bryant 90I furnace before to get temporary heat for our home.  It was a lifesaver and that is why I wanted to add this post on how to do it on our site.  I have step-by-step instructions below, but if you do not like reading then we have a really good YouTube video made by David Vermullen on, “Hooking up a gas furnace to a generator” below. Thanks to Mr. Vermullen for taking the time to make this excellent informative video! Here is my step by step instructions:

  1. Tools needed: screwdriver, electrical tape, wire stripper, wire nuts, heavy-duty extension cord, 2000 watt minimum generator, voltmeter to make sure power is turned off and make sure generator is producing enough voltage. The generator should produce at least 110 volts AC with the furnace running.
  2. Make sure that the power to the furnace is turned off at the breaker box in case the power is restored while you are working on the furnace’s wiring! When the electric company restores power you will of course turn the generator off, disconnect the extension cord, reconnect the power wires to the furnace using your home’s power source then turn the breaker back on.  Always test with a volt-meter to make sure the power is off when working with electricity. Hopefully, you have the individual breaker marked for the furnace in your breaker box so you will know which breaker turns the furnace power off and on.  If you do not have the breaker marked then I would recommend turning all your home’s breakers off to make sure the power does not come on while you are wiring your furnace to the generator. I would suggest making sure that the furnace’s wall thermostat is turned off as well.  I would suggest turning the thermostat off or way down because you do not want the furnace to come on until you have the power hooked up and running with the generator. 
  3.  Make sure the power is turned off to the furnace by testing with a voltmeter.
  4. Remove the junction box cover plate that covers the power switch for the furnace with a screwdriver.
  5. Remove the power switch and connect the wires from the extension cord (white and black) to the two power wires that go into the furnace using wire nuts.  You would connect the white wire from your extension cord to the white neutral wire of your furnace. You would connect the black wire (power wire) from your extension cord to the black power wire of your furnace. Use electrical tape to wrap wire nuts so they do not come off. Wire nut or tape off the bare wires that come from your home’s power source to the furnace because you do not want live wires exposed when the power company restores power to your home. Make sure that the furnace’s blower door is installed because many furnaces have blower door safety switches that cut off power to the furnace if the blower door has been removed.
  6. Plug the heavy-duty extension cord into the generator power source with the generator running. Make sure that the generator is running outdoors. Never run a generator indoors to prevent carbon monoxide poisoning. 
  7. Turn up the thermostat and hopefully see the furnace start and fire up. Congratulations! Fantastic! Awesome! 

An important note: This should work on most gas furnaces that have one transformer systems (most furnaces do).  If you have a system that has two low voltage transformers one on the indoor furnace and one on the outdoor unit then this might not work. It still might work with a two transformer system but the low voltage wiring would need to be investigated to see if the furnace’s transformer is used for heating. If the outdoor unit’s transformer is used for heating then it would not work because with this power set up the furnace would not be getting low voltage to make the furnace run.  In other words, if the outdoor unit (Air Conditioner) has a low voltage transformer that is used to control the heat then this will not work because the outdoor unit requires 220 volts to power the outdoor transformer. If you have any questions please email me anytime at or comment below. We would love to help you out and earn your business! 

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