Gas Furnace Features from Consumer Reports

Furnace Buying Guide

Replacing the old furnace in your central heating system with a new, more efficient model can offset volatile energy prices. Money aside, today's furnaces pollute less and boost comfort by producing heat more steadily than older furnaces. Gas is the most common heating fuel and this report focuses on gas furnaces.

Features

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.

Dual heat exchanger

Heat exchangers are the components that draw heat from the burned gas. To draw more heat from the air they burn, energy-efficient furnaces supplement the primary exchanger with a second exchanger. Because the exhaust gases in that second exchanger might yield a corrosive acidic condensate, the second exchanger is made of stainless steel, lined with plastic, or otherwise protected.

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. That's especially true if sections of the home have different heating or cooling requirements—because of wide variations in the number or type of windows, for example. But contractors we interviewed said that furnaces connected to zoned ductwork generally require more repair.