Generator Wattage for a Furnace: What Listings Say

What a Furnace Needs from a Backup Power Source

This article answers the shopping question behind the phrase generator wattage for a furnace: how the wattage figures in a generator listing relate to a furnace in your Florida home. Furnaces are used on cool mornings and during occasional cold snaps, so heating is one of the loads Florida homeowners consider when they shop for backup power.

Every forced-air furnace uses electricity for the blower motor that pushes warm air through the ducts. A gas or oil furnace gets its heat from fuel, but the blower, ignition, and controls still draw electricity. An electric furnace uses electricity for the heating elements as well as the blower.

The furnace's nameplate states its electrical requirements, and the installation manual states them in the wiring section. The generator listing states its own figures in watts. Reading both is the only way to compare them.

Gas, Oil, and Electric Furnaces as Listing Terms

The words gas, oil, and electric on a furnace listing describe how the furnace makes heat, not how a generator is built. A gas furnace burns natural gas, an oil furnace burns heating oil, and an electric furnace heats with electric resistance elements.

The fuel type changes the electric load. A gas or oil furnace needs power for the blower and controls. An electric furnace needs power for the blower, controls, and the heating elements. The nameplate lists each part's requirement.

Gas and oil furnaces produce carbon monoxide during combustion. Follow the furnace maker's manual for maintenance and venting, and read the CDC carbon monoxide page listed in the sources below.

Running Watts and Starting Watts on the Listing

Electricity is measured in watts, a unit of power, as the EIA Measuring electricity page explains. Generator listings state 2 figures: running watts and starting watts.

Running watts are the continuous load a generator can supply. Starting watts are the extra load a motor draws for a moment when it starts. The furnace's blower motor is the part of the load that needs the starting figure.

The generator running watts and starting watts article explains how the 2 figures read on a listing. The generator wattage calculator article covers how listing titles present them.

Generator Classes for Furnace Backup

Portable generators and standby generators are sold in size classes that correspond to their stated running watts. The classes are useful as shopping terms when you compare a furnace load to a listing. A small portable generator states running watts at the lower end of the range; a mid-size unit states more; a large unit states the most. The exact figures are in the listing title and bullet list.

For a gas or oil furnace, the blower and controls often draw below the running watts of many portable generators. For an electric furnace, the heating elements add a much larger load. The best 3000 to 5000 watt generators for hurricanes guide covers the mid-size class; the best large portable generators for hurricanes guide covers the larger class. A standby generator guide covers the permanently installed option.

Reading the Furnace Nameplate and the Generator Listing

The furnace nameplate lists voltage, amperage, and wattage for the blower and controls. An electric furnace nameplate also lists the heating element load. Read that label before comparing generator listings.

A generator listing rarely states an appliance result such as furnace compatibility. It states watts, outlets, fuel, and features. Use the stated running watts and starting watts as the figures to compare with the furnace label.

When the listing does not state a detail you need, that is normal. "Not stated by the seller" is a reading outcome, not a fault. The maker's page for the generator and the maker's page for the furnace provide the figures.

Furnace Backup Power in Florida

Florida homes may use a furnace, a heat pump with a backup electric heating element, or both. The backup power question is the same: what does the heating equipment label state as its electrical load.

The National Weather Service page on what to do before a hurricane tells you to check emergency equipment such as flashlights and generators. The Florida Division of Emergency Management publishes generator safety pages for before, during, and after a storm, and a disaster supply kit checklist.

For a Florida house, a generator for heating is usually chosen from the same pool as a generator for refrigeration and lights. The buying guides below sort generators by stated watts.

What Generator Listings Do Not State About Furnaces

Generator listings do not promise how a furnace will behave on that power, and they do not state a runtime for a specific furnace. They state output watts, fuel, outlets, and features.

For a standby generator, the installer, the maker's sizing materials, and the local permit office decide which model fits the home. This site compares stated details only; it does not size a home.

For a portable generator, the comparison is the same: the stated running and starting watts against the furnace nameplate. The best inverter generators for Florida neighborhoods guide includes models that state these figures for the mid-size class.

What to pick for your situation

Questions

What wattage does a furnace need?

The furnace nameplate states the electrical load for the blower, ignition, and controls. Compare that to the generator listing's stated running watts and starting watts. A listing does not state a furnace wattage result.

Do gas and oil furnaces need less electricity than electric furnaces?

A gas or oil furnace uses electricity for the blower and controls. An electric furnace uses electricity for those and for the heating elements. The nameplate lists the figures.

Can a power station run a furnace?

A power station states a continuous output figure in watts and a capacity in watt-hours. Compare the output figure to the furnace nameplate, and read the maker's page for run time. See the portable power station guide below.

Where do I find the wattage on my furnace?

Look for the nameplate on the furnace cabinet or blower door. It lists voltage, amperage, and watts. The installation manual lists the electrical requirements in the wiring section.

Does a generator listing say if it can run a furnace?

Usually not. The listing states watts, outlets, fuel, and features. Compare the stated running watts to the furnace nameplate.

Should I size a generator for the furnace alone or for the whole home?

The generator listing states a single set of output figures. Compare the running watts to the furnace nameplate for the furnace alone, and compare to the combined nameplate of all appliances you plan to run at the same time. The maker's page and a licensed electrician can help with the full load.

What should I check before using a generator for heating?

Follow the furnace maker's manual and read the Florida Division of Emergency Management generator safety page in the sources. For connecting a generator to home wiring, a licensed electrician, the maker, and the local permit office decide.