If your furnace isn't working on one of these subzero mornings, you might try a cheap and simple fix before you call for professional help: change the filter.
Simple as that is, a clogged furnace filter is still the single greatest cause of service calls that Frank Garro encounters.
“It's very simple, but it's the simplest things that can fool you,” said Garro, who is the chair of the heating, ventilation and air-conditioning program at Ivy Tech. “That's one of the primary causes we see, no matter how cold it is.”
Another simple problem that can choke off a furnace's air supply is one that occurs in high-efficiency furnaces that draw air from outside a house, Garro said.
Sometimes snow can block the outside air intake of such a furnace, and fixing that furnace is as simple as brushing (or shoveling) aside a snow drift that has blocked an intake, he said.
A third simple fix that sometimes works for people with electronic control units on their furnaces is shutting it completely down, then restarting it. But Garro cautioned that if a homeowner tries this approach, he ought to record any diagnostic codes displayed on the panel of the control unit. Restarting the unit might wipe out any such codes, which could help a service technician figure out the problem.
Not all fixes are simple, of course. To catch some of those problems before they become cold-morning crises, Garro counseled people to have their furnaces inspected by professionals at the beginning of every heating season.