The first cold stretch of the year usually sends people straight to the thermostat. If the heat comes on, everything feels fine. But there are a few places outside the house that are worth checking before the furnace begins running every day.
Exterior vents and openings spend months exposed to leaves, insects, birds, rodents and weather. Some may barely be used during spring and summer. By the time heating season starts, a vent that looked clear in March may no longer be clear in October.
A quick walk around the house can catch quite a few problems early.
Furnace Intake and Exhaust Vents
Start with the furnace vents if your heating system terminates through an exterior wall.
High-efficiency furnaces often have white PVC pipes outside the house. One may bring combustion air in while another sends exhaust gases out. The exact arrangement depends on the furnace and the way it was installed, so two similar-looking pipes should not be treated as interchangeable.
Look for anything that clearly does not belong there: leaves, twigs, feathers, nesting material, insect debris or signs that an animal has been using the opening.
Vegetation can cause trouble too. A shrub that was small in spring may be pressing against the vent by fall.
Birds and small animals are another possibility. A sheltered vent can look like a convenient place to investigate during the months when the furnace is rarely running. The first sign of trouble may not appear until the first genuinely cold night.
If the furnace suddenly refuses to start, shuts down after a short cycle, shows a draft-related fault or starts making a new noise at the same time you find nesting material outside, the two things may be connected.
A suspected blocked furnace vent is not something to solve by repeatedly resetting the furnace or pushing a tool into the pipe. The visible material may only be part of the obstruction, and combustion vents are part of a safety system rather than ordinary household ductwork.
Dryer Vents
Dryer vents deserve the same kind of look.
Lint already gives these vents plenty to deal with. Add leaves, damaged flaps, insects or nesting material and airflow can become noticeably worse.
Check whether the exterior flap moves freely and whether lint has collected around the opening. If clothes suddenly take much longer to dry, the vent path is one of the first places worth investigating.
Avoid covering a dryer vent with fine mesh simply to keep animals out. Anything that catches lint can create another restriction.
Bathroom Exhausts
Bathroom fans usually disappear into the background until they stop working properly.
The exterior termination can become dirty, damaged or blocked, especially if it sits under an eave or in another sheltered spot. Birds sometimes make use of these areas as well.
A bathroom fan that becomes unusually noisy or seems to move less air may have a problem at the fan, inside the duct or at the exterior opening.
This matters more once the weather turns cold. Homes stay closed up longer, windows are opened less often, and moisture has fewer easy ways to escape.
Soffit, Gable and Roof Vents
Attic ventilation openings are frequent weak points on older homes and on houses where screens or trim have started to loosen.
Squirrels can enlarge small gaps. Birds may use damaged vents for nesting. Bats can exploit surprisingly narrow openings around rooflines.
You do not need to climb onto the roof to notice many of the warning signs. Look for bent covers, chewed edges, droppings, staining, nesting material or repeated animal activity near the same spot.
The mistake to avoid is sealing an opening as soon as you find it.
If an animal is already inside the attic or wall cavity, closing the entry can make the situation worse. The opening should be checked for current use before repairs are made.
Any repair also needs to preserve the airflow that the vent was designed to provide. Blocking an attic vent completely can trade a wildlife problem for a moisture problem.
Chimneys and Flues
A chimney that has not been used for months should not automatically be assumed clear.
Birds, squirrels and debris can all find their way into damaged or poorly protected chimney openings. In some homes, the same chimney structure may also serve a heating appliance.
From the ground, look for obvious damage to caps or covers and any sign of nesting activity.
If you hear an animal, notice debris in the fireplace or smell something unusual when an appliance starts, stop there rather than trying to burn or blow the obstruction out.
A clear-looking chimney top does not tell you what is happening farther down the flue.
Foundation and Crawl-Space Openings
Cold weather pushes attention upward toward roofs and chimneys, but lower openings are just as important.
Foundation vents, crawl-space doors and gaps around pipes can become entry points for mice, squirrels, skunks and other animals looking for shelter.
Watch for loose screens, digging, disturbed soil, droppings, pulled insulation or worn spots around an opening.
These signs are especially useful in fall because animals begin spending more time looking for protected spaces before winter.
Again, check before sealing. A hole may already be in active use.
Keep Plants Away From Working Vents
Overgrown landscaping causes more trouble than people expect.
Dense shrubs can hide damaged vent covers, make it harder to see nesting activity and reduce the open space around equipment.
Trim back plants around furnace vents, dryer exhausts, foundation vents and outdoor heating equipment. Fallen leaves should also be cleared away from low openings.
This is not about stripping the side of the house bare. The goal is simply to keep vents visible and unobstructed.
What You Can Check Without Taking Anything Apart
Most of this inspection can be done from the ground.
Take a few photos if something looks wrong. They can be useful later if you need to explain the problem to an HVAC company, pest-control professional or contractor.
Pay attention to what you actually see rather than trying to diagnose the problem immediately.
Is there material in the opening?
Is the vent damaged?
Is an animal still present?
Did an appliance begin acting differently at the same time?
Those details are more useful than guessing at the cause.
There is also a point where inspection should stop. Do not disconnect furnace vent pipes, reach into an unknown opening, climb onto a wet roof or push debris farther into a vent.
If the issue involves a fuel-burning appliance and you have a carbon monoxide alarm, unusual illness, smoke or a possible gas leak, leave the house and treat it as a safety problem rather than a home-maintenance job.
A Five-Minute Walk Around the House Can Be Worth It
Most exterior vents are easy to ignore because they are small and usually work without attention.
That is exactly why problems can sit unnoticed for months.
Before the first long run of cold weather, take a slow walk around the house and look at the furnace vents, dryer exhaust, bathroom vents, attic openings, chimney and foundation vents.
You are not trying to perform repairs during the inspection. You are simply looking for anything that has changed since the last heating season.
Finding a nest, damaged cover or blocked opening in mild fall weather is a much easier problem than discovering it on a freezing night when the furnace will not stay on.