July 26, 2021

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Electrical Backup For A Gas Furnace

Electrical Backup For A Gas Furnace

This article will describe how I can keep my gas furnace operating and warm my house even when electricity is not available from the local power grid.

Know how to keep your gas furnace and air conditioning problems running even when electric power is down!

RELATED: Having a Backup Power Supply

Gas Furnace | Keep Warm Even When Electricity Is Down

What Is a Gas Furnace?

A gas furnace is a furnace powered by natural gas to provide heat in low room temperatures. My gas furnace has a variable speed fan motor to push warm air through the vent ducts in our home.

A single power cord connects the furnace fan motor and the thermostat to 120 VAC power.

1. Gas Furnace with AC Power Connection



During a recent cleaning and maintenance check, the service technician took a number of measurements that I recorded for reference and future design planning. The furnace is quite efficient.

It draws 2.0 Amps under normal operation and 3.9 Amps when the variable speed motor is operating. The maximum draw is at 5.0 Amps using a clamp-on multimeter.

This means that 10.0 Amps is likely the highest surge current expected for this furnace’s variable speed motor.

2. Digital Clamp-On Multimeter for Measuring Actual AC Current Draw

Electrical Backup For A Gas Furnace

As I mentioned in the last article, my solar power system uses a Sunny Boy 3800TL-US SMA inverter with a secure AC electrical backup socket. The actual socket connection is under the cover.

3. Inverter with 120VAC, 12.5A Backup Power

Electrical Backup For A Gas Furnace

This inverter can produce 1500 watts of 110 volts AC and can provide 12.5 amps if grid power goes out and the sun is still shining. I need just 5.0 amps, so the secure power from the inverter works just fine during sunny days.

4. Configuration Providing 120VAC Backup from the Solar Array

Electrical Backup For A Gas Furnace

Since a solar day here is about 7 hours long, I need another way to produce electricity for the 17 hours my solar panels aren’t producing power. I decided to use the Honda 2200i portable generator.

RELATED: The Grid-Tie Inverter: Electrical Backup for Your Refrigerator-Freezer

5. Gasoline-Powered Electric Generator

Electrical Backup For A Gas Furnace

The 2200i has several external power sockets and can produce 2200 watts of 120VAC using unleaded gas. The 1-gallon gas tank in the 2200i can keep the generator going for about 5 hours—9.6 hours if the economy burn rate is set on the generator.

It’s been quite dependable—and quiet.

6. Generator Driving a Natural Gas Furnace

Electrical Backup For A Gas Furnace

Connecting a 6-gallon marine gas tank to the 2200i gave me a 7-gallon power system that can drive this generator for between 35 and over 67 continuous hours—normal setting or “economy” setting.

7. Power Cord From the Furnace Plugs



This shows how to power your furnace with a solar or gas-powered generator during a power outage.

8. Generator with Expanded Fuel Storage for Over 67 Hours of 120VAC

Electrical Backup For A Gas Furnace

By adding multiple 6-gallon gas tanks, you can run a generator continuously for days, but this single tank design is essentially all I need to provide 24/7 back up and keep my home warm and comfortable while electrical power is out.

Multiple gas tanks just mean fewer refills. During operational tests, the inverter secure power supply and the gas generator worked just fine and provided power to keep the furnace working as desired.

Except for the time to disconnect from the SMA inverter and plug the furnace into a power cord from the Honda 2200i generator, I experienced no downtime of significance.

I used the economy setting for the generator, which gave me approximately 9.6 hours of run time for each gallon of fuel.

During sunny conditions, the generator would be used approximately 17 hours each day, so the 7-gallon fuel supply could easily provide over five days of furnace operation—or indefinitely by refilling the marine gas tank periodically while the sun-driven SMA inverter was providing power to the furnace.

Even on sunless days, the generator could drive the furnace for 67 hours continuously before gas refill would be required.

Home heating and air conditioning were major concerns for me, and the SMA secure power and gas generator configuration met the challenge.

My wife is happy as she no longer worries about heating and cooling our house and keeping food cold during emergency situations, and I’m happy because the issue of finding a source for emergency power backup for these major appliances has now been resolved.

Watch this video by Word of Advice TV for some helpful furnace maintenance tips:



Maintaining the heat in your home is very important especially in the cold seasons. With the right solar panel setup, the absence of electricity is not a problem to power up your gas furnace.

It’s a great back up for keeping warm in emergency situations.

Do you have your own electricity back up for your gas furnace at home? Tell us in the comments section below!

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Editor’s Note: This article was originally published in May 2019, and has been updated for quality and relevancy.

Last update on 2021-02-20 / Affiliate links / Images from Amazon Product Advertising API