Snow, Ice, and Your Furnace Vents: A Western Montana Winter Checklist

Every winter in Western Montana, some of the no-heat calls I get have nothing to do with a broken part. The furnace or boiler is fine. It shut itself off because snow, ice, or frost blocked the pipes it breathes through. The good news is that this is one of the easiest problems for a homeowner to spot and prevent.

I've spent more than ten years doing HVAC work around Missoula and the Bitterroot, and here's what I'd want every homeowner and building owner to know before the snow really starts piling up.

Which systems this applies to

Most newer high-efficiency gas and propane furnaces, and many high-efficiency boilers, don't vent up a chimney. Instead they use two plastic pipes, usually white PVC, that run out the side of the house or up through the roof. One pipe pulls in fresh air for combustion. The other carries exhaust out.

Because these pipes often come out low on a side wall, they can end up buried by drifting snow, a shoveled pile, or snow sliding off the roof. If either pipe gets blocked, the system's safety controls are designed to shut it down. That's a good thing, because it keeps exhaust from backing up, but it also means you lose heat until the pipe is cleared.

If you're not sure what kind of venting you have, go outside and look where your furnace or boiler sits in the house. Two pipes poking out of the wall or roof nearby is the usual giveaway.

If your furnace is already blowing cold air, see Furnace Blowing Cold Air? Common Causes in Missoula Homes.

What to check after a storm

After a heavy snow or a windy night, take a minute to walk around the house:

• Find both pipes and make sure the openings are clear. Gently brush away snow by hand or with a broom. Don't chip at ice with a shovel or anything sharp, since PVC can crack.
• Look for frost or ice buildup on the exhaust. In very cold weather, the exhaust can build up frost right at the opening. A little is normal, but a growing ice plug isn't.
• Don't pile shoveled snow near the vents. It's easy to bury them without thinking when you clear a walkway or driveway.
• Watch the roofline. Snow sliding off a metal roof can bury a side-wall vent in seconds.
• Clear around your gas meter carefully, too. Brush snow off by hand rather than kicking or hitting it.

If the heat stopped and you find a blocked vent, clearing it may let the system restart on its own. Some systems need to be reset or may need a service visit to get going again. If it doesn't come back on, or keeps shutting off, call us.

The condensate line: a hidden winter problem

High-efficiency furnaces and boilers make water as they run. That water drains through a small tube, often to a floor drain or a small pump. If that line runs through a cold space or outside, it can freeze. When the water can't drain, the system will often shut down.

If your furnace keeps shutting off during cold snaps and the vents look clear, a frozen or clogged condensate line is a common cause. It's worth having it checked so the line can be routed or protected properly.

Heat pumps need clear space, too

If you have a heat pump, the outdoor unit needs room to pull air through it. Keep snow cleared away from the sides and top, and don't let a roof drip line build ice on it. It's normal for a heat pump to go into a defrost cycle in winter, and you may see some steam. A unit that's encased in solid ice, though, needs attention.

Carbon monoxide: don't skip this

Blocked venting is one reason a working carbon monoxide alarm matters. Make sure you have CO alarms on every level of your home and near sleeping areas, and test them. If a CO alarm goes off, get everyone outside and call 911. If you smell gas or propane, leave the house and call your gas utility or propane supplier from outside. Don't try to troubleshoot either one yourself.

Rentals and multi-unit buildings

If you own or manage rentals or a multi-unit building, vents near walkways and parking areas get buried by plows and shoveling more than anywhere else. It helps to let tenants and snow-removal crews know where the vents are, and to mark them so they don't get covered.

A tune-up catches the rest

During a heating tune-up, we check that the venting is sloped and supported correctly, that the condensate drain is flowing, and that the safety controls are doing their job. If your vents were installed somewhere that keeps getting buried, we can talk through whether rerouting them makes sense.

ProCare Climate works on all furnace, boiler, and heat pump brands for homes and businesses in Missoula, Lolo, Frenchtown, Stevensville, Hamilton, Polson, and across Western Montana. Learn more about our furnace repair in Missoula, boiler service, and heat pump installation.

Heat out, or want your system checked before the next storm? We're open 24/7. Call 406-546-1289, or request a free install estimate on our site.