How to Prepare Your HVAC System for Winter

What You Can Do Yourself

Replace the air filter. If you haven’t changed the filter since the end of cooling season, now is the time. A clean filter ensures the furnace can move adequate airflow — which matters for both efficiency and safety. Restricted airflow is the leading cause of furnace short cycling and high-limit switch trips.

Test the thermostat. Switch from COOL to HEAT mode and set the temperature 5 degrees above current room temperature. The furnace should ignite within a few minutes. If it doesn’t — or if you hear clicking without ignition — something needs diagnosis before cold weather arrives.

Clear the area around the outdoor unit. If you have a heat pump, the outdoor unit runs year-round. Clear leaves, debris, and any vegetation that accumulated over the summer. Adequate airflow around the unit matters in heating mode as much as cooling.

Check vents and registers. Walk through the house and make sure supply vents and return air grilles aren’t blocked by furniture, rugs, or stored items. Blocked returns restrict airflow throughout the whole system.

What a Technician Should Check

Furnace ignition and burner operation. The igniter, flame sensor, and gas valve all need to function correctly on the first call for heat. A technician verifies ignition sequence, flame sensor reading, and proper gas pressure.

Heat exchanger inspection. The heat exchanger separates combustion gases from the air that circulates through your home. Cracks in the heat exchanger can allow carbon monoxide into the living space. Visual inspection and combustion analysis during a fall tune-up catch this before the heating season starts. If you haven’t had the heat exchanger inspected in 3–5 years, schedule it.

Carbon monoxide detector. Not an HVAC inspection item, but worth checking while you’re in the mindset: replace CO detector batteries and test the units. A functioning CO detector is the backup safety net for the heat exchanger inspection.

Blower motor and belt (if applicable). Older systems with belt-driven blowers need belt inspection and tension adjustment. Direct-drive blower motors need amperage measurement to identify early bearing wear.

Flue pipe inspection. The exhaust flue carries combustion gases out of the home. Blockages, corrosion, or disconnected sections can cause dangerous backdrafting.

The Dallas Winter Reality

DFW winters are genuinely mild most of the time — and then genuinely not. A single winter can include 60°F days in December and a hard freeze in February. The challenge is that a furnace that’s been dormant since March faces its first real demand on a very cold night rather than a gradual warm-up.

The technicians we send out on cold-snap emergency calls in December frequently find furnaces that would have been fine with a $150 tune-up in October. A failed igniter, a dirty flame sensor, a cracked flue connection — all of these show up as “furnace not working” at 11 p.m. on a 25°F night. They’re much easier and cheaper to address in October.