A guide to choosing furnace size, efficiency, and features
Replacing or improving a furnace may not pay off as handsomely as it did during the energy crisis of the late 1970s. But it may deliver steady, modest savings. And efficient heating isn’t only about money. Because today’s furnaces burn less fuel to generate heat, they are less polluting than their predecessors. Some models with modulating heat output can produce heat more continuously than older furnaces, increasing comfort.
Heat pumps that wring heat from the ground or from outdoor air (and reverse the process in summer, to act as an air conditioner) are the preferred way to heat in the South and Southwest, and oil furnaces have a niche in older homes, mostly in the Northeast. But the majority of new central-heating systems use a gas furnace, the focus of this report.
The Basic Choices
How do most people go about buying a furnace? First, they contact contractors. To prepare this report, we did, too. More than 500 specialists in residential heating and air conditioning told us about their experiences in installing and maintaining heating equipment.
The major manufacturers of gas furnaces are American Standard (Trane), United Technology (Carrier, Bryant, Heil, Tempstar, and Comfortmaker brands) and Goodman (Janitrol and Amana). Other brands include Rheem (Ruud), and Lennox (Armstrong). All offer furnaces in a range of capacities and efficiencies, and we think manufacturers generally deliver on those specifications. Each brand offers a generally similar array of key features.
The degree of similarity between manufacturers’ offerings is one reason this report does not include Ratings of furnaces by brand. The most important steps in selecting a furnace, we think, are to ensure that the unit’s specifications fit your needs, that it is bought from a contractor who installs it well, and that it’s adequately maintained. Our survey results help confirm that view: When we asked about the most common reasons for service calls for furnaces, about twice as many contractors we surveyed cited human error—inadequate maintenance, for example, or improper installation—as cited defective equipment.
How Large a Furnace?
When it comes to furnaces, size counts—a lot. A furnace that’s too small won’t keep the house comfortable during extreme cold. Partly to avoid that possibility, most installed furnaces are too large for the home they’re installed in. Cost is only one of the problems with such a unit. Compared with a correctly sized furnace, a furnace that’s too large will cycle on and off more frequently. That puts more wear on its components, wastes energy, and may cause the temperature to vary uncomfortably. Also, upgrading to a larger furnace may require the installation of bigger ducts to accommodate the increased airflow. Without proper duct sizing, the airflow can be noisy.
To be sure of correct sizing, choose a contractor who agrees to take the time to calculate heating needs using an industry-standard calculation.
