Getting Your Furnace Ready Before the First Hard Freeze

Every October, the first night that drops into the twenties fills our phone lines with homeowners who turned on the furnace for the first time since April and got nothing. Most of those failures were avoidable. Here is how to spend an hour in September so you are not one of those calls.

Turn it on now, while it’s still warm out

Set the thermostat to heat and raise it a few degrees above the room temperature. Listen. You should hear the inducer motor start, a click or two, the burners light within a minute, and the blower come on shortly after. Let it run fifteen minutes and feel the warm air at a register. If anything in that sequence does not happen, you have found your problem in September instead of January, and we can get to it without a wait.

A faint burning-dust smell on the first run is normal and clears quickly. A smell that persists, or any smell of gas, is not. Shut it off and call.

Replace the filter

Write the date on the frame. One-inch filters generally need changing every one to three months during the heating season; four- or five-inch media filters last six months to a year. A clogged filter is the leading cause of furnace shutdowns we see, and it is a two-minute fix.

Clear the outside pipes

If your furnace is a high-efficiency model, find the two PVC pipes that come out through an exterior wall. Make sure they are clear of leaves, nests and overgrown shrubs now, and remember where they are for after the first big snow. If they sit less than a foot or so above where snow typically piles, mention it when you schedule your tune-up; raising them prevents a shutdown every storm.

Check the condensate drain

High-efficiency furnaces produce water. Follow the small drain line from the furnace to the floor drain or condensate pump and make sure it is not kinked, clogged or disconnected. A blocked drain will shut the furnace down on a safety and can leave a puddle in the utility room.

Test the carbon monoxide detector

Press the test button, replace the battery, and check the date on the back. Detectors expire, usually after seven to ten years. Every home with a gas furnace, water heater or boiler should have a working detector on each level and near bedrooms.

Open the registers and clear the returns

Walk the house and make sure supply registers are open and not blocked by furniture or rugs. Check that the return grilles are unobstructed. Closing registers in unused rooms does not save energy on a forced-air system; it raises the pressure in the ducts and can trigger the same overheating that a dirty filter does.

Schedule the tune-up

The things you cannot check yourself are the ones that cause the serious failures: a cracked heat exchanger, a weakening igniter, an inducer motor on its last bearings, gas pressure that has drifted. A fall tune-up covers all of them with a camera, a meter and a combustion analyzer, and the report tells you what is weakening so you can decide whether to replace it now or wait. Book it in September or early October, before the schedule fills with the no-heat calls that a tune-up would have prevented.

If your home has a boiler

The same logic applies. Fire it now, bleed any radiators that gurgle or stay cold at the top, check the pressure gauge against the range your technician noted last year, and schedule the fall service. Boilers are forgiving machines, but they reward attention before the season rather than during it.