Leaf-Fall Vent Patrol: Keep Combustion Air & Exhausts Clear Before First Frost

Why It Matters in London and the Area

Southwestern Ontario gets a long leaf drop in October and November, and it often overlaps with the first cold nights. That is the point in the season when furnaces, fireplaces, and water heaters start to run longer. Natural Resources Canada and other Canadian safety sources remind homeowners that fuel-burning appliances must be vented properly to remain safe and efficient. If the vent or fresh air intake is buried in leaves, wet snow, or an animal nest, the appliance can trip the safety switch, shut down, or start venting in the wrong direction. Doing a vent patrol now prevents many no-heat calls later.

Find Every Exterior Termination First

Many homes around London have more than one exterior vent. Your furnace may be side vented, your HRV/ERV may have two hoods, the dryer may be nearby, and a heat pump or air conditioner may be right under the soffit.

• Locate every round or rectangular hood, especially low ones, on the driveway or side yard.
• Look behind shrubs, window wells, and decks where leaves collect.
• Note which pipes are the furnace exhaust and combustion air intake. These must stay clear at all times.
• If you are unsure which pipe is which, do not open or disassemble anything. Make a note and contact M&K to have a technician confirm it during a fall visit.

Finding all the terminations comes first. You cannot protect a vent that you do not know is there.

One-Evening Clear-Out: Leaves, Seed Pods, and Lawn Debris

Once you know where all the terminations are, clear a safe space around them.

• Remove leaves, seed pods, grass clippings, and fall garden debris.
• Create 24–36 inches of open space around the vent or intake to allow air to move freely.
• If the vent sits over river stone or mulch, rake or scoop out anything that has blown against the wall.
• Keep kids’ toys, bins, patio cushions, and fall décor away from vent locations.
• Do not remove screens or termination parts yourself. If a vent keeps plugging, have M&K adjust or replace it.

Do not cover or box in the vent for appearance; terminations must stay open. If you need leaf/screen protection, ask M&K for a code-approved option. Furnace and combustion air terminations must remain open. If you need to shield them from leaves, ask M&K about code-safe options.

Check Screens, Slope, and Signs of Blockage

Most sidewall vents have a slightly sloped termination, sometimes with a screen. Screens help keep animals and large debris out, but they can also hold wet leaves and ice.

Check for:

• screens that are matted with leaves or pet hair
• terminations that hold water instead of draining away
• pipes that look pushed out of alignment
• black streaks, soot, or icing around the vent

If you see frost in mild weather, soot, or ice forming where it shouldn’t, that can be a sign of poor venting. That is the point where you should stop and call M&K Heating and Air Conditioning. Homeowners can clear debris. A licensed technician must do combustion and venting diagnostics.

Do Not Block Combustion Air

Some homes bring combustion air in through a dedicated pipe. Others get it in through a grille in the mechanical room. That air is part of the appliance’s safety features. Never block it with storage, paint cans, holiday boxes, or extra filters. If the furnace or water heater pulls air from the room and the room cannot supply it, the appliance can backdraft. Health Canada and Ontario fire/safety guidance recommend that homeowners test CO alarms regularly and have fuel-burning appliances serviced annually. Your fall vent patrol is the homeowner’s part of that safety plan. The technician visit is the other half.

What to Watch For After the First Frost

Even if you do a perfect cleanup, conditions change when we get the first freeze-thaw in London.

Watch for:

• The furnace shuts down a few minutes after it starts
• Error codes that come back after you reset the furnace
• Ice forming on or under the vent
• Strong exhaust smells near the vent
• Dryer or HRV air that seems weaker than normal

Any of those can mean the vent is freezing, the slope is not ideal, or there is another obstruction deeper in the system. Book M&K for diagnostics or a fall Maintenance Plan tune-up so a technician can check the venting, combustion, and drainage while the weather is still workable.

Pair the Vent Patrol With a Professional Tune-Up

Your one evening checklist protects the system’s exterior. A professional visit protects the inside. During a fall tune-up, an M&K technician can:

• Inspect the heat exchanger and burners
• Confirm venting is clear and correctly sloped
• Check that combustion air is not blocked
• Test CO and safety devices
• Verify filters and airflow so leaves in the yard are not pulled into the return.

That is also the best time to ask about Maintenance Plans, so the furnace, heat pump, or hybrid system is checked every year without you having to remember it.

If you see frost, soot, repeat shutdowns, or are not sure which vents belong to which appliance, book an appointment with M&K Heating and Air Conditioning for diagnostics or set up a fall Maintenance Plan visit.