HVAC Furnace Vent

Published on August 28th, 2018 | by Henri


Furnace intake freezes up in winter

Q.  My question concerns the exhaust/intake pipe for our forced air oil furnace. The exhaust pipe is inside the intake pipe. Both are mounted outside the house about one foot above ground level. We are told that this is within Town code and cannot be changed.

The problem is that during the winter, drifting/blowing snow accumulates between the exhaust and the intake pipe. Since the exhaust is hot it melts the snow. When the heat is off the melted snow freezes into ice on the lip of the intake pipe. After several times of this happening the ice clogs the intake pipe and air cannot be brought into the furnace. Because the furnace cannot draw any air, it shuts down.

We must constantly check and clear the ice from the vent or we have this recurring problem. Is there anything we can do to prevent this from occurring? Is there some type of cover that we can attach that diverts the snow while at the same time allows enough air to enter the intake pipe.
Jut so you know we live in central Massachusetts.

Thank you and we look forward to any information you can provide.

A.    The standard rule of thumb is that the exhaust/intake pipe should be 12 inches ABOVE THE SNOW GRADE, not 12 inches above ground.
In the northeast, the snow grade is considered to be 24 inches on average, although, with snow drifting, the snow cover may even be greater than 24 inches.

The pipe should be a minimum of 3-feet off the ground and the pipe should slant slightly downward. This may be the cause of your problem.
You may want to have an experienced HVAC contractor look over the situation, see if the pipe  could be changed to allow for more clearance from the ground, or to make other suggestions considering the actual layout of the area around the pipe.

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