As the weather cools down, everyone starts looking for a warm place to stay—and that includes birds, mice, and other small critters. In the fall, it’s common for pests to try to nest inside warm, protected spaces around your home. One of their favourite spots? Your furnace venting system.

Every year, we hear from homeowners experiencing “no heat” issues, only to discover that the cause is not the furnace at all. In many cases, a bird or mouse nest has blocked the chimney or PVC vent pipe, triggering a safety shutdown in the system.

If your furnace is not turning on or showing an error code, pests could be part of the problem. Here’s what to watch for and what you can safely do to check for vent blockages.

Why Pests Choose Furnace Vents

Furnace exhaust vents provide a dark, warm, and protected space that can look like the perfect home for animals preparing for winter. Sidewall PVC vents and vertical chimney vents are both at risk—especially in the fall when birds and mice are actively building nests.

When these pests get into your venting system, they bring along debris like grass, twigs, leaves, or even garbage. All of this can block airflow and cause your furnace to shut down as a safety measure.

Signs You May Have a Blocked Vent

If your furnace has suddenly stopped working or is showing a fault code, a blocked vent could be the reason. Here are some signs to look for:

• Your furnace is running, then shuts off quickly
• You see an error related to flame rollout or pressure switch lockout
• There’s a burning smell when the furnace runs
• You hear scratching or movement near your vents
• You’ve had pest issues in the past

How to Check for a Nest or Blockage

Before you call a technician, it’s worth doing a quick visual check. In some cases, you may be able to solve the issue yourself.

Here’s how:

1. Use a flashlight to look inside the visible vent pipes, both inside and outside your home
2. Look for signs of debris like grass, twigs, or fur
3. If you see something close to the edge, and it is safe to do so, try to carefully remove the debris without pushing it further inside
4. Do not reach too far in or try to disassemble the venting unless you are confident it’s safe

If the blockage is deep or you can’t get to it, it’s best to stop and call a technician to avoid damaging the system or making the blockage worse.

Can You Use Screens to Keep Pests Out?

Many homeowners wonder if a mesh screen could stop pests from getting in. While this seems like a good idea, it can create a bigger problem in winter.

Screens on furnace vents tend to freeze over in cold weather, blocking airflow and causing furnace shutdowns. This can be dangerous and leave you without heat when you need it most.

Instead, if you’ve had pest issues in the past, try this:

• Use old nylon stockings or breathable fabric over PVC vent ends during the warmer months only
• Make sure to remove them before winter to avoid ice buildup
• Do a seasonal check in spring and fall to look for nests or signs of activity

Why This Matters in the Grande Prairie Region

In Northern Alberta, fall comes fast and winter hits hard. Homes need reliable heat, and a blocked vent is one of the fastest ways to knock your furnace out of service.

Since many pest-related blockages happen quietly, the first sign of a problem is often when the furnace stops working. Taking a few minutes to check your vents in the fall can help you avoid a costly or stressful call when the temperature drops.

Summed Up for You

Furnace vents may not be top of mind when it comes to fall home maintenance, but keeping them clear can make a big difference. If you notice signs of pests or blockages, act early. A simple flashlight check might be all it takes to keep your heat running smoothly through the cold months ahead.