Snow Blocking Heating Vent

Heating System Flue Blocked By Snow

Furnace Systems

Direct vent heating systems like high efficiency furnaces and water heaters need adequate space to vent outside

If you see white plastic exhaust venting coming from the top of your furnace or water heater you likely have a direct vent system. These vent through the side wall of your building and need to have proper clearance to vent without obstructions.

Even when placed with proper clearance during installation, things like heavy snowfall, snow drifts, and even ice buildup from things such as a roof overhand or a leaking gutter above can block the vent and cause serious safety concerns for occupants inside.

How does the flue vent look?

Here are what common vents look like with adequate and inadequate clearances.

These vents are properly placed high enough over the ground and with a turndown to prevent ice buildup.

The following are the same location but different perspectives.

The flue from this water heater is placed too close to a downspout which can increase risk of ice buildup after heavy snow melt and refreezing.

This perspective shows how low the flue is to the ground. This can easily be covered by moderate amounts of snow and certainly with snow drifts caused by wind-blown snow against the house.

What happens if a flue becomes obstructed?

If a direct vent water heater or furnace becomes blocked it can either shut down if the proper safety sensors are in place and working, or worse, if the system does not shut down, then the exhaust fumes from the gas combustion within the unit will back flow into the house which is a major safety risk for occupants inside.

How to help prevent your flue from becoming blocked?

First, it is important that the flue is properly installed to an adequate height from the ground. If ice buildup occurs, find out where it is coming from. If melting snow is falling from a roof or gutter, then proper repairs will be needed to stop the water leaks. If that is not enough and snow drifts occur, then you must shovel the snow away from the area regularly. As an added precaution, some circumstances may require adding snow fences in front of the flues or building a shelter around the vent, of course being careful not to obstruct air flow. It may be necessary to contact an HVAC professional if these do not solve the issue or if water (condensation) is leaking from the flue and causing a build-up which indicates an issue with the flue slope.

Cabon Monoxide detectors should be installed and tested regularly to help prevent risk of carbon monoxide poisoning in the event of a blockage such as this.

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