Maintenance

Fall Furnace Checklist for Seattle Homeowners: 9 Things to Do Before the First Cold Snap

Published September 25, 2026

Your 9-step fall furnace checklist

1. Replace the air filter

This is the single most important thing you can do. A clogged filter makes your furnace work harder, can cause it to overheat and shut down, and pushes dust through your home. If you had wildfire smoke this summer, your filter is likely worse than it looks.

2. Test the thermostat

Switch it to Heat and raise the setpoint 5 degrees above room temperature. The furnace should start within a few minutes. If you have a battery-powered thermostat, replace the batteries now so it doesn't die on a cold night.

3. Do a test run — and use your nose

Let it run for 15–20 minutes. A faint dusty smell at first is normal. A smell that doesn't fade, or any rotten-egg gas odor, is not.

If you smell gas: don't flip switches or use your phone indoors. Leave the house and call your gas utility from outside.

4. Check and clear every vent

Walk the house and make sure supply registers are open and return grilles aren't blocked by furniture, rugs, or storage bins. Blocked returns are a common cause of rooms that never warm up.

5. Test your carbon monoxide detectors

Every home with a gas furnace needs working CO detectors, ideally on each level and near sleeping areas. Press the test button and replace batteries. Most detectors need replacing every 5–10 years — check the date on the back.

6. Clear the area around the furnace

Garages and basements collect clutter over summer. Keep boxes, paint, cleaning products, and anything flammable at least a few feet away, and make sure the furnace has room to breathe.

7. Look at the flame (if you can see it)

On many gas furnaces you can see the burner flame through a small window. A healthy flame is steady and mostly blue. A lazy yellow or orange flame can indicate a combustion problem and is worth having checked.

8. Check the outside vent

High-efficiency furnaces vent through PVC pipes on an outside wall. Make sure they're clear of leaves, nests, and debris — a blocked vent will shut the furnace down.

9. Listen for new noises

Some hum is normal. Banging when the burners light, squealing, grinding, or rattling are early warnings. Problems caught now are usually cheaper than a breakdown in January.

Warning signs to call a pro

• The furnace short-cycles (turns on and off every few minutes)
• It runs but blows cool air
• Some rooms are much colder than others
• The pilot or ignition fails repeatedly
• Yellow flame, soot around the furnace, or a CO alarm
• Your heating bill jumped without an obvious reason
• The furnace is 15+ years old and struggling

What a professional tune-up adds

The checklist above covers what a homeowner can safely do. A professional tune-up goes further: cleaning burners and the flame sensor, inspecting the heat exchanger for cracks, testing ignition and safety controls, checking gas pressure and electrical connections, and testing for carbon monoxide. It's the best way to catch small issues before they turn into a no-heat emergency.

If you're thinking about the bigger picture — an older furnace, high bills, or adding summer cooling — it's also a good time to ask about heat pumps. We'll give you honest repair-vs-replace advice and help you find any utility rebates you qualify for.

Yeti Heating & Air services furnaces across Seattle, Bellevue, Kirkland, Redmond, Renton, Shoreline, Lynnwood, Bothell, Edmonds, and Everett, with upfront pricing and licensed, insured technicians.

Book your fall tune-up: call (206) 823-0670 or request a callback.