Your 15-Minute Fall Furnace Checklist
Do this once in the fall, before you actually need heat. Finding out the furnace doesn't work on the first 35-degree night is a bad time — techs are slammed, and you'll wait. Fifteen minutes now buys you a warm, uneventful winter.
The checklist
- Replace the air filter. Start the heating season with a clean one. Check the size printed on the old filter's frame and note the airflow arrow direction.
- Test the heat early. Switch the thermostat to Heat, set it a few degrees above room temp, and let it run for 10–15 minutes. A dusty burning smell on the first run is normal — it's dust burning off the heat exchanger. It should fade quickly.
- Check every vent. Walk the house and confirm supply vents are open and not blocked by furniture, rugs, or curtains. Return vents need clear space too.
- Test your CO detectors. Press the test button on each one. Replace batteries if they're not hardwired with battery backup. No CO detector on each floor? Fix that before heating season — this is non-negotiable with any fuel-burning furnace.
- Look at the outdoor exhaust vent. For high-efficiency furnaces, find the PVC vent outside and make sure it's clear of nests, leaves, and debris. For standard furnaces, glance at the flue/chimney area for anything obviously blocked or damaged.
- Clear space around the furnace. The area around the unit should be free of boxes, paint cans, and clutter — especially anything flammable.
- Listen. While it's running, listen for new bangs, rattles, squeals, or booms at startup. A quiet hum is normal; new noises are worth noting.
- Check the condensate drain/trap. High-efficiency furnaces produce condensate too. Make sure the drain line is clear and draining.
- Look at the flame (gas furnaces with a sight glass). A steady blue flame is what you want to see. Yellow, flickering, or rolling flames mean call a pro.
- Schedule a pro tune-up if it's been over a year. A technician checks gas pressure, the heat exchanger for cracks, electrical connections, and safety controls — things outside DIY territory.
Call a pro when…
- The furnace won't start, short-cycles, or blows cold air
- You see a yellow or erratic burner flame
- The CO detector alarms (leave first, troubleshoot never)
- It's been more than a year since a professional servicing
Fifteen minutes, once a year. That's the whole job. For the video walkthrough, find me at HVAC DIY Help on TikTok and YouTube (@hvac_diy_help).