If you live on one of the newer streets off Spring Creek Rd. or in the Marz Subdivision, your furnace probably has no chimney at all. Instead, two white plastic pipes come out through the side wall of the house, usually a little above the ground. They are easy to forget about until the first good snowfall, when they become the most important thing on the outside of the house.
West Lincoln's population is projected to more than double, and the Smithville Master Community Plan (OPA 63) enlarges the urban area to make room for it. That means a lot of households are living with a condensing furnace for the first time. Here is what those pipes do, what tends to go wrong with them, and how carbon monoxide fits into the picture.
Two pipes on the side wall do the job of a chimney
A high-efficiency furnace pulls so much heat out of its exhaust that what is left is cool enough to run through plastic pipe. One pipe brings outdoor air in for burning the gas. The other carries the exhaust out. Because the exhaust cools so much, it also leaves water behind, and that water (the condensate) drains through a small tube to a floor drain or a little pump.
The furnace watches its own venting. A pressure switch checks that air is moving through the pipes before the burners light. If either pipe is blocked, the furnace shuts itself down instead of running. In most cases a blocked vent means a cold house rather than a dangerous one, which is the way it is designed. Still, that safety switch is the last line of defence, not something to lean on all winter.
Snow and frost are what usually block them
For early November, Environment Canada's Hamilton forecast page lists a normal daytime high of 8°C and a normal low of 0°C, so furnaces around here are already running regularly by late autumn. By the time the real snow arrives, the furnace is working hard, and that is when the pipes get buried.
The usual culprits are drifts that pile up along the side of the house, snow thrown off the driveway by a snowblower, and snow sliding off the roof. During a long cold spell, the exhaust pipe can also grow a cap of frost from its own moisture, slowly closing it off. A few habits help a great deal:
- Find your two pipes before the first snowfall, and if they are on a side of the house you rarely walk past, put a tall marker stake beside them.
- Do not pile shovelled snow against that wall, and aim the snowblower chute somewhere else.
- After a storm or a windy night, take a look. Clear snow away by hand or with a soft brush.
- Do not chip ice off the pipes with a shovel or knock them with anything hard. The pipe and its fittings can crack, and a cracked exhaust pipe is a much bigger problem than a frosty one.
- Keep firewood, bins, barbecue covers and outdoor furniture well away from the pipes, in every season.
- If frost keeps building up on the exhaust no matter how often you clear it, that is a sign the venting needs a closer look.
The condensate line is the other cold-weather weak spot. If it runs through a cold garage or close to an outside wall, it can freeze, the water backs up, and the furnace shuts off. Water around the base of the furnace, or a furnace that quits during the coldest nights and comes back once things warm up, points that way.
When the venting itself needs to change
Sometimes the problem is not the weather but where the pipes ended up. A vent that comes out too close to the ground for our snow, under a deck that was added after the house was built, or tucked into a corner where drifts collect will keep causing trouble. In Ontario, gas appliances and their venting are installed to the CSA B149.1 Natural Gas and Propane Installation Code, which sets out clearances from the ground, windows, doors and the gas meter. Raising or rerouting a vent has to meet that code, so it is not a weekend project.
The cost depends on how far the pipes need to move and what is in the way inside the wall. In general, rerouting a vent is a much smaller job than replacing a furnace, and it is often worth doing if the house has a vent that ices up every winter.
Older houses have a different venting question
The old village core along Griffin Street, Canborough Street and Station Street has the opposite situation. Many of those houses started out with wood or coal, were converted to oil and then to gas, and still have a tall masonry chimney. When an old furnace there is replaced with a high-efficiency one that vents through the side wall, the gas water heater can be left alone in a chimney that was built for a much bigger fire. A cold, oversized flue may not draw properly, and the water heater's exhaust can spill back into the basement.
The usual fix is a liner sized for the water heater, or a different venting plan for it. If you are planning a replacement in an older home, ask about the chimney before you sign anything. Our furnace installation and replacement page explains how sizing and venting fit together, and the guide on what size furnace a Smithville house needs covers the sizing side.
Carbon monoxide: what every household with a gas furnace should know
Carbon monoxide is a gas you cannot see or smell. It comes from fuel that burns poorly or from exhaust that ends up indoors. In a house, the common sources are a blocked or disconnected vent, a cracked heat exchanger in an ageing furnace, a water heater spilling back from its chimney, and a car left running in an attached garage.
The early signs are easy to mistake for the flu: headaches, dizziness, nausea and tiredness, often in more than one person at once, that ease off when you leave the house.
The Ontario Fire Code requires a working carbon monoxide alarm next to each sleeping area in any home with a fuel-burning appliance, a fireplace or an attached garage. Most new houses in town have at least one of those, and many have all three.
- Put an alarm outside each sleeping area, and consider one near the furnace room as well.
- Test the alarms monthly and change the batteries when they ask for it.
- Check the end-of-life date printed on each unit. Alarms wear out and need replacing even if they still beep when tested.
- A smoke alarm does not detect carbon monoxide unless it is a combination unit that says so.
- If an alarm sounds, get everyone outside, call the fire department from outdoors, and do not go back in until they say it is safe.
- Have the furnace and water heater checked before they run again.
A yearly check matters more on these furnaces
A proper tune-up before the cold arrives should include a look at the vent terminations outside, cleaning the condensate trap and line, testing the pressure switch and inducer, and checking combustion. On furnaces that have been running for many years, like the ones in the established homes around Station Meadows, a careful inspection of the heat exchanger matters most. Our furnace and AC maintenance page covers what a seasonal visit looks at.
Who should work on the furnace and its vents
Under Ontario Regulation 212/01, gas appliances must be installed, serviced and repaired by a registered contractor using qualified gas technicians (G1, G2 or G3). Work is performed by TSSA-certified gas technicians. A proper installation also matters for the manufacturer's warranty, so keep your paperwork when anything on the venting is changed.
If your side-wall vents keep icing up or the furnace keeps shutting off in the cold, Smithville Heating Cooling can look at it through our furnace repair service.