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DIY Q&A – Furnace & Generator Questions & Answers

The A/C Sine Wave

Thought I would post some of the questions and answers I’ve been asked about recently regarding High Efficiency Furnaces and using a standard or inverter type generator . If you would like to ask a question email me at rick@ ricksdiy.com


Q: Will a high efficiency furnace with it’s electronic control board work with a generator? Was the furnace you worked on one with a control board? I’m thinking about the electricity put out by a generator compared to that of the power company. Thanks for your help.

A: Yes The furnace on the video did have a control board. Just a little background; The control board is powered by low voltage as most electronics are, it gets it’s power via a transformer that converts the 120 Volts A/C to most likely 5-12 Volts D/C. Because of the transformer it helps condition the power. This makes it safe to use most any generator on the furnace.

The main concern is that you don’t want to shut off the generator or run out of gas while the furnace is running this may cause a severe drop in voltage and cause the fuse or breaker to open on the furnace. But other than that it won’t damage anything, you would just have to replace the fuse or reset the breaker. I will have to do a video to show this as many people have concerns about that.

Q: I always thought you needed an expensive generator with inverter to run furnaces with control boards. Does generator need to be physically grounded, as with rod and wire? I have a Briggs and Stratton generator and a Coleman Powermate with a Subaru ohc engine, and neither one mentions using a ground rod. Since they are portable generators is it OK to use them as is to power my furnace without a ground rod?

A: It is recommended to ground your generator but I doubt many do, even on construction sites I’ve seen them ungrounded with the electrical inspector walking around. If you have a location where you always run your generator I recommend to get a grounding rod, I use 1/2″ rebar myself as they sell these nice plastic caps you can place over the top so you don’t impale yourself. Plus much cheaper than a copper or brass rod.

Drive the rod (At least 36″) into the ground with 2-4″ sticking up, place the orange cap on top to easily locate and protect. You can use an old set of jumper cables to connect the generator to the ground or install a copper ground line with screw tight connectors to easily remove. I set mine up with one end of a jumper cable permanently mounted to the generator…makes it quick and easy for anyone to use.

I have more questions and answers but I would like to hear from you, let me know what kind of questions you have and what kind of DIY videos you want to see in the future..


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  1. Bob says:

    Great website…great videos. I watched the video on how to wire your furnace to be able to connect it to a generator. My home is heated with a natural gas powered Weil-McLain boiler (92% effiency) installed in 2012. TWO QUESTIONS: #1 In your video you showed how to convert the hard wire of the gas furnace to a plug in style connection to a single receptacle…Could I complete a similar conversion for my boiler? Or does that method only really apply to a furnace? #2 The manufacturer said that it should NOT be run off of a standard generator producing “dirty power” and that due to its “sensitive electronics” could only be run off of a generator producing the “pure sine wave” electricity. The generator that I currently own is a standard generator and does not produce the pure sine wave. These other generators are really expensive and I am not going to buy one. Any ideas how to get around this and still run my boiler off of a my standard generator?
    I really would appreciate your thoughts.

    1. Rick says:

      I have been fighting this problem from the manufacturers myself. There is so much confusion from not only the various manufacturers, to the electronic components suppliers to the power companies. I have studied this for many years and have real world experience working on Stand By Generators.

      Some of my clients have been huge data farms, switch sites and cellular network providers. They all use traditional power generators that use Modified Sine Wave Generators but they feed that power through a capacitor bank most of the time. That helps with the harmonics which can cause problems on a larger scale. I have no problem recommending using a traditional generator with a HE (High Efficiency) type furnace or boiler. I have a 98% HE Rinnai Water Heater, and I have run it on my old generator with no issues.

      The control board in your boiler is powered by low voltage as most electronics are, it gets it’s power via a transformer that converts the 120/240 Volts A/C to most likely 5-12 Volts D/C. Because of the transformer it helps condition the power and it also has capacitors on the board and all modern motors have built in capacitors. This makes it safe to use most any generator.

      The main concern is that you don’t want to shut off the generator or run out of gas while the unit is running this may cause a severe drop in voltage and cause a fuse or breaker to open on the unit. But other than that it shouldn’t damage anything, you would just have to replace the fuse or reset the breaker.

      I will say that I do recommend possibly getting a single unit transfer switch, due to demand from friends and family I’m currently in the process of manufacturing my own with my business. I’ll be listing them on Amazon and my site in about 2 weeks, just waiting for my new front panels to get in.

      I’ve included a picture of my original versions that I have made for years. The new ones are stainless steel and I will have an Install Video that almost anyone can do. Perfect for powering just a furnace, or boiler or any other hardwired appliance.

  2. Pam Riberts says:

    I recently connected a generator 6250 Troy built to a gas furnace with electronic board. The furnace started kicking on as off many times. I increase load in the house to draw some electric power away from the furnace to see if this would help. Also decreased power on other appliances. Heater worked a little while correctly when connected to main power source but now kicks on and off many times . Any ideas out there of what to do??

    1. Rick says:

      Hi Pam, could you give some more details on what your furnace did or didn’t do?

  3. Rich says:

    I have a rudd natural gas furnace that when plugged into a generator the power exhaust blower will come on then the burner will ignite but only stay on about 10 seconds. Any ideas? Thanks

    1. Rick says:

      Hi Rich, I think I need some more info, but maybe try grounding your generator to your furnace.

    2. Beth says:

      We just encountered a similar problem. We were connecting our G26 Lennox gas furnace to a Westinghouse WH7500E generator. Turns out this “standard” generator would not work with our high efficiency furnace. Our HVAC company just lent us an “inverter” type generator called the Honda EU2000i. That solved the problem immediately. Thank goodness, because we have had no power for four days now as a result of the ice storm this week.

  4. hyman says:

    connecting external power to a furnace,I am planning to use a 1500 watt inverter. can you send me a link or info about using a non-sine wave inverter on a lennox 1/3 HP motor. confused about non-sine wave and sine wave inverter to us on the furnace, mainly for the motor.
    thank you

    1. Rick says:

      hi Hyman, I’ve done some posts about using inverters, wiring is no different then wiring anything else, just be sure to ground your inverter. Some inverters require the neutral to be switched and some may only work if the neutral and ground are bonded together. Sorry can’t give you any other info. Sine vs non sine is over hyped, your circuit board has built in capacitors and transformer which helps condition the power so non sine inverters can work most of the time.

  5. John Garey says:

    Have a Buderus GA124 gas boiler attached to Nest thermostat.I have installed a DPDT switch to operate boiler off a grounded Honda 3500 kw generator. Does not operate off generator power nor does Nest operate say it is not getting voltage. At the boiler thermostat attachment reads 24 volts a.c.. Nest says it is only getting 1.24 volts any ideas?

  6. james t cavanaugh says:

    I had someone from happy hiller come out the filter was dirty so I changed it they said everthing is alright.
    Now its doing it again. Its been like 25 at night. The furnace comes on but it does not want to shut off. I have to get
    up and turn it down one notch to get it to shut off. Does it have a overload where it will shut down eventually.

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About Rick

I've been an HVAC/R Mechanic working in the Seattle area for over 15 years, specializing in the commercial service industry.. I’m also a Licensed Electrician & Gas Piping Mechanic and have numerous other trade related certifications. I’ve instructed at local trade schools and now continue teaching through this site.

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