Wiring your gas furnace to a generator is a project that’s frequently either over-thought or not thought of at all. Some people think you need a high dollar transfer switch wired to your breaker panel, thus requiring a Electrician or you have to temporary rewire the breaker to the generator for temporary power and then rewire everything once the power comes back.
But this isn’t the case, NEC (National Electric Code) simply requires that appliances must be on their own dedicated circuit. By simply rewiring your furnace you can have the ability to use your furnace by powering it with a portable generator.
When the power is out you simply disconnect the furnace from the outlet and connect it to a extension cord. You run this cord outside to your generator, start the generator and once it is sufficiently running you plug the furnace in and use it like you normally would, go to the thermostat and crank up the heat. In this way you can use your generator and fuel more wisely and only as needed.
video: An Overview: How To Wire Your Gas Furnace To A Generator
The cost for the materials for this particular job was less than $20, and all can be found at most hardware or big box stores.
The tools can be much more basic than this, the drill is a little overkill but if your installing the Outlet box onto your furnace with sheet metal screws than the drill will be needed.
As is the case every and anytime your working around electricity you MUST check that the power is OFF and then CHECK AGAIN. You can never be too careful when it comes to this point. Even after all these years I still get shocked, it’s rare but like driving a car sooner or later your going to be in an accident, hopefully it will be a manageable one.
Turn Off your breaker or light switch that controls your furnace. Keep in mind that a high number of Breaker panels are mislabeled. Open your furnace and find where your power is coming in from, most likely one of the sides. Trace it down to the junction box or in my case simply the circuit board.
Pull off any covers and then test for voltage. I like to use the Fluke Voltage Stick first, But you first must make sure it works on a live circuit and then you can test it out. After you have verified the power is off, carefully remove the wire nuts and test with a Voltage or Multi-Meter. Once you are darn sure there is no power then you are safe to work on it.
Write down or label your wires if they are not the normal BLACK (Hot), WHITE (Neutral) & GREEN (Ground). Some might be Red, Orange, Brown etc. You must rewire it exactly as it was. Black to Black, White to White and Green to Green/Ground.
Pull the wires out to the outside of the furnace, at this time you can either wire in the POWER CORD or install the outlet box.
In the video I install the OUTLET BOX first. I put the conduit with the wires coming from the breaker into the Outlet Box and then level it where I would like to mount it. Screw it to the wall or furnace with the appropriate screws.
Next you need to wire in your Single Receptacle Outlet, You may need to cut back your wires and strip them at this point. This is hard to explain in text and is better understood in the video. Wire your Black or HOT to the smaller bladed side of the outlet, if your facing the outlet this will be the Right side this screw is normally Brass/Gold in color, the White or Neutral wires up the larger bladed side this screw is usually silver in color, and then the Green or Ground goes to the last terminal that is bonded with the metal framework of the receptacle, sometimes this screw will be Green colored, but every manufacturer is different.
Once that is wired you must carefully push the receptacle back into the outlet box and screw it in, put on the COVER PLATE and were ready to move onto the final part.
Installing the POWER CORD, Next part we have to add in the CABLE CONNECTOR to where the old power cable came into the Furnace, once you have the cable connector in you can pull through the Power Cord and secure it down.
Now you must rewire the power cord to the connections on the furnace, if your using wire nuts be sure to Double Check that the wires are secured by tugging on each individually and then taping the connection with some electrical tape. You can further secure with tie straps if needed.
Make sure to put back on any cover plates, double check that everything is wired properly and secured. At this point you can turn the power back on and check the outlet with your meter (Not Shown In Video) to make sure everything is wired properly. Now you can plug in your furnace and check operations.
Now that your done you can test it out with or without your Generator, I recommend to do a test run on a Dark Rainy Night so you know what it’s going to be like when your going to have to use it.
There are many variations of this including different types of plugs and wiring methods, I have done this many times and have had several pass electrical inspections. As stated in My Disclaimer always check with your local code or city regulations as to what is required.
If your interested in getting the 2011 NEC Code Book and your going to get it online help me by buying it through my link, Thanks.