Winter HVAC Maintenance Checklist Before First Frost

Your furnace, boiler, or heat pump does most of the work once temperatures drop. A few quick checks help catch problems before they cause a breakdown.

Thermostat Testing

Switch your thermostat from cooling to heat and set it a few degrees above room temperature. Listen for the equipment to start, confirm warm air comes out of the registers within a few minutes, and watch to make sure it runs a full cycle instead of shutting off early.

Burner Flame Check

If you heat with natural gas or propane and your furnace has a viewing window, check the flame there. Don’t remove panels to look. The flame should be steady and blue. A yellow, flickering, or uneven flame means the fuel isn’t burning cleanly and needs a technician.

Boiler Check

For hot-water boilers, check that the pressure gauge reads within the normal range marked on it, look for leaks around the boiler and radiators, and bleed any radiators that stay cold at the top.

Flue Pipes and Exhaust Venting

Exhaust has to leave your home freely through the chimney or PVC exhaust pipes. Check the outside vent openings for leaves, nests, or insect blockages from the summer, and clear anything in the way so carbon monoxide vents outdoors.

Carbon Monoxide and Smoke Detectors

Test every smoke and carbon monoxide detector in your home, and replace any CO detector past the date printed on the back. A technician should test the furnace’s safety switches during a tune-up, since homeowners can’t check those safely.

Optimizing Airflow and Indoor Air Distribution

Restricted airflow makes the blower work harder and wears out motors and the heat exchanger faster. Opening up air paths keeps air moving evenly through your ducts.

Change the Furnace Filter

A fresh furnace filter keeps dust off the blower motor and keeps air moving across the heat exchanger. Check your filter every month and replace it when dirt covers the surface. Homes with pets or near unpaved roads usually need to change the furnace filter more often.

Clear Vents and Return Grilles

Walk through your rooms and check floor, wall, and ceiling registers. Make sure drapes, rugs, and furniture aren’t blocking them. Closing vents in unused rooms can throw off the air balance in your ducts, so leave them open.

Inspect Visible Ductwork for Leaks

In unheated basements, crawlspaces, and attics, look over the exposed duct joints. Gaps in supply ducts leak heated air into unheated spaces, and gaps in return ducts pull cold air into the system. Sealing the seams you can reach with mastic or foil tape keeps warm air in your ductwork and headed where you need it.

Winterizing Outdoor Units and Auxiliary Components

Outdoor equipment needs attention too.

Preparing Your A/C for Winter

Turn off the electrical shutoff switch near your outdoor A/C condenser. Skip this if your outdoor unit is a heat pump, since it provides your heat in winter. Clear dead plants, leaves, and overhanging branches within two feet of the unit. You don’t need to wrap it in plastic, but a board or breathable cover on top keeps falling icicles from bending the fan blades.

Heat Pump Winter Prep

Make sure the outdoor unit sits on its pad or riser above the snow line, clear snow from around it after storms, and don’t cover it. It needs open airflow all winter. Keep firewood and shovels away from the coil.

Humidifier Setup

If your duct system has a bypass or power humidifier, replace the water panel before heating season. Move the seasonal damper to the winter position and set the humidistat so indoor air doesn’t get too dry.