What should I do to get my furnace ready for winter?
Learn where the furnace switch and gas shutoff are, change the filter, clear the furnace area and the outdoor vent pipes, check the condensate drain, test your carbon monoxide alarms, set up the humidifier, and run the heat on a mild day. Leave burners, gas pressure and the heat exchanger to a technician's tune-up.
Key points
- Do this list in September or early October, before the first cold night.
- Know where the furnace switch and gas shutoff are before you need them.
- Mark the PVC vent pipes outside so snow and the snowblower stay clear of them.
- Run the heat on a mild afternoon so a weak part shows up while a fix is easy to schedule.
- The technician's side is a separate list: gas pressure, combustion, heat exchanger and safety switches.
To get a furnace ready for a Minnesota winter, find the furnace switch and gas shutoff, change the filter, clear the furnace area and the outdoor vent pipes, check the condensate drain, test the carbon monoxide alarms, restart the humidifier, check the propane tank if you have one, and run the heat on a mild day. That's the homeowner's list: an afternoon with a flashlight, a new filter and a step stool. The technician's side (gas pressure, combustion readings, the heat exchanger and safety switches) is a different job, covered in our post on what a furnace inspection covers.
Do this in September or early October. A furnace that sat all summer gets its first real test on the first cold night, and a problem you find on a 55-degree afternoon is much easier to deal with than one you find at 10pm in November.
The checklist at a glance
| Task | When | Who |
|---|---|---|
| Find the furnace switch and gas shutoff | Once, and show everyone in the house | You |
| Change the filter and write the date on it | Now, then every 1–3 months for a 1-inch filter | You |
| Clear the furnace area and the return grille | Now | You |
| Check the PVC vent pipes outside and stake them | Before the first snow | You |
| Test the condensate drain or pump | Now | You |
| Test CO and smoke alarms and check their dates | Now | You |
| Replace thermostat batteries, if it uses them | Now | You |
| New humidifier pad, water on, damper set | When the heat comes on | You |
| Check the propane tank level | Before the deep cold | You and your supplier |
| Run the heat on a mild day | Late September or early October | You |
| Tune-up: gas pressure, combustion, heat exchanger, safety switches | Early fall | Technician |
Before you start: the switch and the gas shutoff
Find two things and make sure everyone in the house knows where they are.
- The furnace switch. Usually a plain light switch on the side of the furnace or on a nearby wall or joist. It cuts power to the whole furnace. Use it any time you open a furnace panel.
- The gas shutoff. A valve on the gas pipe near the furnace. When the handle runs in line with the pipe, gas is on. Crosswise is off. Propane homes also have a shutoff at the tank.
If you ever smell gas, don't flip switches or try to find the leak. Get everyone out, then call your gas utility or 911 from outside.
How often should you change the furnace filter?
Change the filter and write the date on it. A standard 1-inch filter usually needs changing every one to three months, more often with pets or remodeling dust. A 4- or 5-inch media filter usually lasts six months to a year. Check the airflow arrow and buy the winter's supply now while you know the size. Very high-MERV 1-inch filters can choke airflow on some furnaces; our filter guide explains MERV ratings.
Clear the space around the furnace. Summer storage creeps toward the furnace. Keep boxes back to the clearances on the furnace label, and keep paint, gasoline, solvents and laundry chemicals away from any furnace or water heater that pulls combustion air from the room. Make sure the return grille isn't blocked, then vacuum the dust around the base of the furnace and the return.
How do you check furnace vents before winter?
High-efficiency furnaces vent through two white PVC pipes out a side wall or the roof (sometimes a single pipe-in-pipe fitting). Outside, pull out leaves and nests, and look for cracked or sagging pipe. Inside, check that the joints are tight and the pipes still slope back toward the furnace. Before the first snow, push a tall stake in next to the pipes so you can find them after a storm and the snowblower doesn't hit them. Drifts and frost can block these pipes and shut the furnace off; our post on clearing a frozen furnace vent covers that.
Older 80% furnaces vent through a metal pipe into the chimney, usually shared with the water heater. Look for rust, gaps at the joints, or a section that has slipped apart. Don't touch it while the furnace or water heater is running; it gets hot.
The condensate drain. A high-efficiency furnace makes water. Follow the small drain tube from the furnace to the floor drain or to a condensate pump. If there's a pump, pour a cup of water into it and make sure it kicks on and empties. A plugged trap or a dead pump will shut the furnace down, and water on the floor under the furnace needs a technician.
Alarms, humidifier and fuel
Carbon monoxide and smoke alarms. Minnesota law requires a working carbon monoxide alarm within 10 feet of every sleeping room. Press the test button on every CO and smoke alarm, replace batteries, and check the end-of-life date printed on each alarm. Replace any that are past it. Our guide to CO alarm placement covers where they belong. A furnace tune-up adds a carbon monoxide reading at the furnace itself, but it doesn't replace alarms by the bedrooms.
Whole-home humidifier. Put in a new water panel (the pad) if yours uses one, turn the water supply back on, and if there's a bypass damper on the duct, set it to its winter position. Then set the humidity by the weather: roughly 25–35% in cold weather and lower in deep cold. If the windows start to frost, turn it down. Our humidifier guide goes into the settings.
Propane. Outside the gas lines, check the tank gauge now and schedule a fill before the deep cold, when delivery schedules get busy. Keep a clear path to the tank all winter. If the price is on your mind, our post on propane heating costs walks through the math.
Run a test cycle on a mild day
If your thermostat takes batteries, put fresh ones in first; a dead thermostat battery is a no-heat call you can avoid. Then set the thermostat to heat and raise it several degrees above room temperature. Watch and listen:
- The inducer fan starts (a whirring from the furnace).
- The igniter glows or clicks.
- The burners light, and they stay lit.
- The main blower starts a minute or so later and warm air reaches every register.
A dusty smell for the first few minutes of the season is normal. Our post on turning the furnace on for the first time this fall covers what else is normal on that first run. And while you're outside, leave the air conditioner uncovered; our post on covering your AC in winter explains why.
If the test run doesn't go right:
| What happens | Common cause | What to do |
|---|---|---|
| Nothing at all | Furnace switch off, a tripped breaker, dead thermostat batteries, or the blower door not seated on its safety switch | Check those four, then call |
| Inducer runs, burners never light | Igniter, pressure switch, or a blocked vent or condensate trap | Check the outdoor vent pipes, then call |
| Burners light, then go out after a few seconds, over and over | Often a dirty flame sensor | Clean it or call; see furnace won't ignite |
| Burners run, but the blower never starts | Blower motor, capacitor or control board | Turn it off at the switch and call |
| Burning plastic or hot wiring smell | An electrical or motor problem | Turn it off at the switch and call |
| Water on the floor under the furnace | Condensate trap, line or pump | Call, and check the pump in the meantime |
What does a furnace tune-up add to a DIY checklist?
Your list keeps the furnace breathing and draining. A tune-up measures the parts that wear out: igniter, flame sensor, inducer, gas pressure, combustion and carbon monoxide, blower amps and the safety switches. Our maintenance service is $129 for a furnace tune-up or $219 for furnace and AC together, the same price for a furnace tune-up in Minneapolis as everywhere else we work. If the test run turns up a problem, a repair visit is a $79 trip charge, waived when you approve the repair. If you'd rather not remember to book every fall, ask us about a maintenance plan. Call 612-429-3465 to get on the schedule before the first cold week.
Questions
When should I get my furnace ready in Minnesota?
September or early October. The first real cold night tends to hit every furnace in the area in the same week, and a furnace that sat all summer gets its first hard test then. Doing your checks and booking a tune-up before that week means any weak part turns up on a mild day instead of a cold night.
Can I clean my own furnace?
You can change the filter, vacuum dust from around the cabinet and return grille, clear the vent pipes outside, and check the condensate drain. Leave the burners, gas valve, gas pressure and heat exchanger to a technician. Some homeowners clean their own flame sensor, which is fine if you shut off power and gas first and follow the steps carefully.
Do I need a tune-up if the furnace ran fine last winter?
Yes, because a furnace can run fine right up to the day a part fails. The igniter, flame sensor, inducer and capacitor all wear gradually, and a tune-up measures them before they quit. A yearly visit also leaves a service record, which helps with warranty claims since some manufacturers expect regular maintenance. With us a furnace tune-up is $129.
What's the difference between this checklist and a furnace inspection?
This list is what you can safely do with a flashlight and a new filter. A furnace inspection is what a technician measures with instruments: gas pressure, combustion and carbon monoxide, temperature rise, flame signal, blower amps and the safety switches, plus a look at the heat exchanger. Do both. They catch different problems.