Furnace System GuideSystems index
Furnace Types: Gas, Electric, Oil, and High-Efficiency
Compare furnace system families: gas furnaces, electric furnaces, oil furnaces, and high-efficiency condensing furnaces, with how each heats, vents, and fits your home.
Electric Furnaces: How They Heat and Operating Cost
An electric furnace turns electricity directly into heat with resistance elements, so nearly all the electricity it draws becomes heat at the point of use. The catch is operating cost, since electricity often costs more per unit of heat than gas and uses far more energy than a heat pump.
System typeGas Furnaces: How They Heat, AFUE Tiers, and Venting
Gas furnaces burn natural gas or propane to heat air, then a blower pushes that warm air through the home's ducts. Their efficiency is rated by AFUE, and federal rules are pushing the whole category toward higher-efficiency designs.
System typeHigh-Efficiency Condensing Furnaces: Secondary Heat Exchanger and Payback
A condensing furnace adds a second heat exchanger to reclaim heat from exhaust gases, pushing AFUE above 90 percent. That extra hardware raises the price but cuts fuel use, and federal rules are making these designs the standard.
System typeModulating Furnaces: Fine-Tuned Heat at the Top of the Range
A modulating furnace adjusts its burner output in small increments instead of stepping between fixed levels. This page explains the design, the high AFUE it reaches, and how manufacturers describe it.
System typeOil Furnaces: Efficiency, Tanks, and Maintenance
Oil furnaces burn heating oil stored in an on-site tank and are common in the Northeast, where petroleum is still a meaningful heating fuel. Their efficiency is rated by AFUE, with ENERGY STAR models certified at 87 percent AFUE or greater.
System typeSingle-Stage Furnaces: How All-or-Nothing Heating Works
A single-stage furnace runs its burner at one fixed output, fully on or fully off. This page explains how that design heats a home, where its efficiency lands, and how manufacturers describe it against staged models.
System typeTwo-Stage Furnaces: High and Low Heat in One Unit
A two-stage furnace has a burner that runs on a low setting most of the time and steps up to high only when needed. This page explains the design, the efficiency it reaches, and how manufacturers describe it.
System typeVariable-Speed Blower Furnaces: What the Motor Actually Does
A variable-speed blower furnace uses an ECM motor that ramps airflow up and down instead of running at one fixed speed. This page explains the motor, its comfort effect, and how manufacturers describe it.