A Timeline for Heating System Care

The essentials

1. Check your furnace filter monthly during heating season and replace it when dirty; many disposable filters last one to three months.
2. Run a full test of the heating system in late summer or early fall, before the first cold night, when repairs are easier to schedule.
3. Test carbon monoxide and smoke alarms every fall in any home with gas, oil or propane equipment.
4. Schedule a professional tune-up once a year, ideally around the fall time change, covering the heat exchanger, gas pressure and safety controls.
5. Consider replacement if the system is more than 10 years old, needs frequent repairs and energy bills are climbing.

Heating is the biggest single item on a winter utility bill, accounting for almost half of the average family’s winter energy costs, according to the Department of Energy. Most breakdowns that leave a house cold start as small, preventable problems: a clogged filter, a blocked vent, a worn sensor. The trick is doing the right task at the right time of year. This calendar lays out the work season by season and separates what you can safely handle from what belongs to a licensed technician.

Monthly During Heating Season: Filters and Vents

The filter is the one part of your heating system you should touch every month. Hold it up to a light; if little or no light passes through, replace it. Many disposable filters last one to three months, but check monthly and change when dirty, since dust, pets and long run times all shorten a filter’s life.

A dirty filter restricts airflow, which increases furnace run time, adds wear on the motor and raises energy consumption. A severely clogged filter can overheat the heat exchanger and trip a limit switch, a common cause of a furnace that runs for a few minutes, shuts off and tries again. ENERGY STAR also warns that a dirty filter can raise energy costs and damage equipment, leading to early failure.

While you are at it:

• Walk the house and make sure supply and return vents are open and not blocked by furniture, rugs or curtains.
• Keep about two feet of clearance around an outdoor heat pump unit, clear of leaves and stored items, because it needs airflow during heating season too.
• If your filter sits in a return grille or an attic air handler, note the size so replacements are easy to order.

Filters with a MERV rating of 6 or higher trap pollen, dust mites and mold spores, but the higher the rating, the more a dirty filter restricts airflow, so follow your equipment manufacturer’s guidance. HVAC Air Filters: Sizes, MERV Ratings and When to Change Them explains how to balance filtration with airflow.

Early Fall: Test Run Before Cold Weather

Late summer through early fall, before the first cold night, is the best window for a test run. Set the thermostat to heat and raise the setting a few degrees above room temperature. The furnace or boiler should start, run steadily and shut off cleanly when the thermostat is satisfied. Confirm that warm air is reaching the registers or that radiators are heating evenly.

Then look around the equipment. Keep the area around the cabinet clear of stored boxes, paint and dust. On a gas furnace, glance at the burner flame through the viewing port; steady blue is what you want, and flickering yellow or orange flames are a reason to call a technician. A brief dusty smell on the first run of the season is common as dust burns off, but a strong or persistent odor, loud banging or repeated shutdowns are not normal.

If anything goes wrong here, you will be glad you found it in September rather than during a cold snap.

Fall: Carbon Monoxide Checks and Detector Batteries

Any fuel-burning furnace or boiler produces carbon monoxide, a colorless, odorless gas that can cause severe illness or death with prolonged exposure. The heat exchanger separates combustion gases from the air your family breathes, and cracks that develop over years of heating cycles can let carbon monoxide leak into the home. That is why heat exchanger inspection matters so much, and why working detectors belong in every house with gas, oil or propane equipment.

Homeowners should:

• Test every carbon monoxide and smoke alarm and replace batteries as needed.
• Replace any detector past the service life printed on the back by the manufacturer.
• Never ignore a detector that chirps or shows a fault; replace it.

Many technicians also test carbon monoxide detectors as part of an annual maintenance visit. Smoke and Carbon Monoxide Alarms: Where to Put Them and How to Test Them covers placement and testing in detail.

Each Year: Chimney, Flue and Combustion Air

Gas and oil equipment needs a clear path to vent exhaust and a supply of combustion air. You can do the visual part: check that the flue pipe running from the furnace or boiler is intact, connected and free of visible rust or gaps, and that vent terminals outside are not blocked by debris, nests or snow. Anything beyond a look, including internal chimney inspection and combustion safety testing, belongs to a licensed technician with the right instruments.

Fall is also a good time to deal with heat loss around the venting itself. Gaps around chimneys are among the worst air leaks in a typical house, along with plumbing penetrations and recessed lights in insulated ceilings. Sealing those leaks and insulating heating ducts in unheated attics and crawlspaces can prevent heat losses of up to 60 percent at the registers, according to the Department of Energy’s Federal Energy Management Program.

Every Few Years: Circulator Pumps and Zone Valves

If you heat with a boiler, the circulator pump moves hot water to your radiators or baseboards, and zone valves direct it where the thermostats call for it. These parts fail gradually, and the first sign is often a room or floor that stays cold while the rest of the house heats fine. There is no fixed replacement schedule; have a technician evaluate them during regular service if you notice uneven heating, new noises near the boiler, or a pump that seems to run constantly.

Use these slower intervals as a checkpoint for the system as a whole. If your furnace or boiler is more than 10 years old, needs frequent repairs and your energy bills are climbing, ENERGY STAR says it may be time to think about replacement rather than another repair. ENERGY STAR figures show that a certified gas furnace sold in the northern half of the country can run as much as 18 percent more efficiently than a baseline model, cutting energy costs by an average of $160 a year. Models labeled for the South, where homes need less heat, deliver as much as 16 percent better efficiency, about $60 a year in savings. Certified oil furnaces offer roughly 4 percent better efficiency, worth about $90 a year. A heat pump is another option, and many ducted units can be installed as drop-in replacements for an existing furnace or central air conditioner.

The Annual Professional Tune-Up and What It Includes

Once a year, ideally in fall before contractors get busy, schedule a professional service visit. ENERGY STAR suggests timing the appointment around the fall time change so it becomes routine.

A thorough visit should include:

• Checking thermostat settings for comfort when you are home and savings while you are away.
• Tightening electrical connections and measuring voltage and current on motors, since faulty connections cause unsafe operation and shorten equipment life.
• Inspecting the heat exchanger for cracks, using a borescope where the whole exchanger cannot be seen directly.
• Checking gas connections and gas pressure, and performing a combustion analysis on the burners.
• Testing the igniter and flame sensor, common culprits in midwinter no-heat calls.
• Checking the condensate drain, which can cause water damage when plugged.
• Verifying system controls so the equipment starts, runs and shuts off properly.

Anything involving gas lines, high-voltage wiring or the heat exchanger belongs to the technician, not the homeowner. The visit is also a good time to ask about thermostats; the Department of Energy recommends programmable models for matching heating to your schedule, and contractors often cite savings of up to 10 percent a year from smart versions.

Related guides

• A Fall Home Maintenance Checklist: fits the heating tune-up into the rest of your fall prep.
• HVAC Air Filters: Sizes, MERV Ratings and When to Change Them: details on filter sizes and ratings for the monthly check.
• A Timeline for Water Heater Care: a matching maintenance calendar for the other major appliance in the utility room.

Common questions

How often should I change my furnace filter?

Check it monthly during heating season and change it when it is dirty. Many disposable filters last one to three months, but pets, dust and long run times shorten that.

When should I schedule a professional heating tune-up?

Late summer or early fall, before the first cold night. Contractors get busy once winter arrives, so an early appointment is much easier to get.

What tasks should I not do myself on a gas furnace?

Leave gas lines, high-voltage wiring, heat exchanger inspection and combustion testing to a licensed technician. Your jobs are the filter, the vents, clearance around the unit and visual checks.

When is it time to replace a furnace instead of repairing it?

ENERGY STAR suggests considering replacement if the equipment is more than 10 years old, needs frequent repairs and your energy bills are going up.

This guide is general information, not professional advice. Follow the manufacturer’s instructions and your local building codes, and hire a licensed professional for electrical, gas, structural or roofing work.