Each brand of furnace offers a similar array of key features, depending on price. The furnace features most often highlighted in product literature and sales pitches are generally the ones found on the higher-efficiency models, but some manufacturers also offer them on premium versions of low-efficiency furnaces.
Variable Speed Blowers
These can deliver air slower, while often making less noise, when less heat is needed. That produces fewer drafts and uncomfortable swings in temperature.
Variable Heat Output
Available on some furnaces that have a variable-speed blower, this feature can increase efficiency and comfort by automatically varying the amount of heat the furnace delivers, usually between two levels. The furnace can thus deliver heat more continuously than could one with a fixed heat output.
Air Filtration
Fitting a furnace with an electrostatic filter, which uses an electrical charge to help trap particles, or a high-efficiency particulate-arresting (HEPA) filter can reduce the amount of dust blown through the heating system. That might help people with asthma or other chronic lung diseases, but there’s little evidence that other people need such filtration.
Ignition System
Fewer and fewer furnaces have a pilot light—a flame that burns continuously, awaiting the next command to ignite the burners. Furnaces with intermittent, direct spark, or hot-surface ignition do away with the constant pilot light in various ways. That increases efficiency and is usually reflected in a furnace’s higher AFUE rating.
Zoned Heating
This feature uses a number of thermostats, a sophisticated central controller, and a series of dampers that control airflow to deliver different amounts of heating or cooling to different parts of the home. The larger the home, as a rule, the more useful zoning is.
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