Today’s more-efficient gas furnaces can save you up to $40 for every $100 you spend on fuel compared with older models. That means that even though replacing a furnace can be expensive, your costs will be paid back over time through lower energy bills.
If you’re replacing your gas furnace or buying a new one, you'll want to check the results of the latest reliability survey by the Consumer Reports National Research Center. The survey covers 21,132 natural-gas furnaces bought between 2008 and early 2014.
Reliability is especially important because when a furnace failed, 77 percent needed significant work. A majority of those broke down completely, with nearly a third producing no heat for more than a day. For 40 percent, the repair cost $150 or more.
If a key part such as the heat exchanger or control module fails, you’re better off replacing the furnace if it’s more than 15 years old (furnaces typically last 15 to 18 years). Otherwise, repairing rather than replacing a furnace might make more sense. If your furnace is on the fritz, try the following before you call a contractor or start shopping, and see our gas furnace buying guide for more details.
Check the filter. If you’re getting low airflow, check the air filter on the furnace. A clogged filter could cut airflow down to a trickle. The highly rated 3M Filtrete 1900 MPR, $20, traps dust better than the usual furnace filter, so it can also help clean the air. Check it monthly, and replace when dirty.
Inspect electrical parts. Loose wires or a thermostat malfunction could also cause heat problems. If your thermostat runs on batteries, try changing them. And make sure that burned-out fuses or tripped breakers haven’t shut power to the fan or circuit board.
Ensure your safety. Every home with a gas or oil furnace should have a carbon-monoxide alarm on each floor and near (not inside) an attached garage. One we recommend is the First Alert CO615, $30. Test the alarm weekly, vacuum it monthly, and replace it every five years. Don’t remember how old the alarm is? Look on the back for the manufacture date.