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I live in New Jersey, and in preparation for future severe-weather-related outages, I would like to have a backup plan in order to power my natural gas furnace, as well as the fridge/freezer and a few lamps. I have a Carrier Performance furnace, installed within the last couple of years.

My main concern is getting a generator that is compatible with the sensitive electronics in the furnace. My initial research has turned a number of articles that indicate the significance of a clean, stable power supply, however I have not found anything more specific than that.

I am currently looking at two paths:

  1. Get a traditional 5000W-7000W generator. A number of these seem to indicate some type of Voltage Regulator, however am I right in thinking that the output they give is still somewhat dirty, with a higher chance of frying the control board in my furnace? The size of this generator should be more than enough to power everything I described previously, along with a few more circuits. I would also think about a conversion kit to give me the option to use propane as well as gasoline.

  2. Get a ~2000W inverter generator, which, as far as I understand, would give much cleaner power, and better gas consumption, but with a more limited output that will reduce the number of devices I can power.

I am not looking at going the whole house generator route, which is beyond my budget. I am in the process of tracking down a good electrician to walk through the plan and discuss install the appropriate transfers switches etc. that may be required.

Am I heading down the right track here, or is there something else I should consider?

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  • @What kind of furnace? Oil? Natural gas? Propane? Heat pump? Coal?
    – wallyk
    Aug 30 '13 at 3:33
  • @wallyk Thanks - It is a natural gas furnace - I have edited my question to reflect this point.
    – Jason
    Aug 30 '13 at 3:54
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    A lot depends on what should be powered. Everybody's list has lights, low power electronics, cable, and internet. But what about cooking, spas and pools, hot water, etc.? What is "must have" and what is "nice to have"?
    – wallyk
    Aug 30 '13 at 5:06
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    You got a propane tank or natural gas coming through pipes from the gas company? In an extended power outage, will the natural gas keep coming (do the gas company's pumps run on electricity...)? If you may get a natural gas outage, your heating backup should be some other media (wood, fuel, butane/propane tank, waste heat from electric generator, etc...)
    – bobflux
    Sep 20 '13 at 9:29
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    The circulation fan will be the biggest power use for the furnace ; Check the wattage of that fan to determine the general amount of power that is needed. Nov 22 '19 at 22:21
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I would not recommend a square-wave/modified-square-wave generator to run your furnace. The control boards in them are particularly sensitive to high-frequency noise induced in those sort of designs. One particular failure mode is that non-sine inputs cause excessive heating in inductive components, whether they be AC motors or current-filtering inductors on the control board.

Looking around, it seems that gas furnaces should be provisioned for 350W, and about the same for a typical refrigerator. 700 watts of steady-state load isn't bad, and I would argue that a 2000W steady-state pure-sine generator could handle the transient loads from start-up currents no problem, leaving plenty of room for laptops (75W - 100W), cell phone chargers (~10W), and lights.

Go with the pure-sine wave.

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Generator output is dirty. But most electronics take AC power and convert it to DC prior to use. This helps for most applicances. You likely don't have to worry about running the furnace and damaging the controls. I would suggest the traditional generator for the whole house, or portion of the house (circuits), unless you have very delicate electronics.

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The least expensive way to power both natural gas furnace and fridge/freezer is to manually plug each, one at a time, into a suitably powerful generator. Both these appliances draw a lot of amperage, especially when starting up. Buying a generator big enough to power both is much more expensive than buying a generator big enough to power one. Also, a bigger generator uses more fuel, and more frequent refueling can be a big bother. During outages, I have run my HVAC and fridge with a generator just large enough for one major appliance. It is a bit inconvenient deciding when to plug each in, but it works. (Usually I leave the fridge plugged in until the house feels cold. Over night, I plug the HVAC in.) Lights draw little power, so you can power the lights at the same time as you power either one of the two appliances.

Some fridges are hard wired into the house circuitry. Fortunately my fridge just plugs in to a wall outlet. So it was easy for me to plug my fridge into a extension cord running to the generator.

Also, an inverter has to run off a battery. The only practical way to do this is to run the inverter off your car battery and leave your car running. It is much more cumbersome to connect an inverter to a car than to plug an extension cord into a generator.

One more thought, a generator has to be run outside, so you might need some sort of roof to protect the generator to protect it from heavy rain and snow. I have improvised with plywood on 2x4 supports and that worked.

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