Five minutes with your furnace before the first hard freeze

The worst night to find out your furnace doesn't work is the first really cold one, because that's the night everybody else finds out too. Here's what you can check yourself in about five minutes, and what you shouldn't try to check yourself.

What you can do

1. Run it before you need it. On a mild day in early fall, set the thermostat to heat and push the temperature up ten degrees. Let it run fifteen minutes. You're testing whether it lights, whether the blower comes on, and whether it holds. A problem found in October is a scheduled appointment. The same problem in January is an emergency.

2. Change the filter, and look at the old one. Not just swap it. Look at what came out. A filter that's grey and loaded means restricted airflow, which makes a furnace short cycle and shortens its life. If yours looks like that after a month, something else is going on.

3. Walk the vents and returns. Furniture pushed against a return, a rug over a floor register, a damper somebody closed and forgot about. Restricted airflow causes a surprising share of the heating complaints we get called out for, and it costs nothing to fix.

4. Smell it, then stop smelling it. A brief dusty burning smell on the first run of the season is normal. That's dust burning off the heat exchanger and it should clear within an hour. A smell that persists, or any smell of gas at all, means shut it off and call.

5. Test the carbon monoxide detector. Push the button. If you don't have one on every level of the house, get them.

What needs a technician

The heat exchanger. A cracked heat exchanger can put combustion gases into the air you breathe, and you can't see it without pulling the furnace apart and inspecting properly. That's the real reason a fall tune up isn't a made up service.

Combustion and gas pressure. A furnace burning incorrectly can still produce heat while wasting fuel and stressing components. Checking it takes instruments, not a look.

The rest of a tune up earns its keep too. Cleaning the flame sensor prevents the most common no heat call we run. Testing the ignitor tells you whether it's about to fail. Checking the auxiliary heat strips on a heat pump tells you whether your backup heat works at all, which plenty of people around here find out the hard way in January.

If the heat is already out

Check the obvious first. Thermostat set to heat and above room temperature, breaker on, furnace switch on, gas valve open, filter not completely blocked. If all of that's fine, call us rather than pulling panels off.

A no heat call in a Missouri January goes to the front of the list.