My furnace exhaust pipe vents out through the roof. How do I prevent ice accumulation from blocking the exhaust pipe? I have a high efficency furnace.
We replaced our gas furnace with a high efficency one this fall. Our furnace is located in the center of the house. Both the exhaust and intake vents are run up through the roof. They are PVC pipes. Previously, we have had issues wiht the intake pipe freezing at the roof line, but never had issues with the exhaust until this winter.
One strategy is to extend the exhaust pipe with a reducer to a larger pipe. This way, if ice accumulates, there's enough diameter to prevent problems.
I'm guessing that you have a 3" PVC vent through the roof deck. Install a 4" to 3" reducer and a 12" length of 4" pipe. You wouldn't even need to glue it on, and I probably wouldn't anyway until you verify that it solves your issue.
If the furnace exhaust vent is a very low to the roof surface type it may very well have been incorrectly installed in the first place. Having this type on your roof is directly implied by your question regarding ice buildup on the roof.
For a more conventional furnace a through the roof furnace exhaust vent system is typical should have several key features as follows:
A high efficiency furnace uses a feature of a concentric piping system where the hot exhaust passes through the center pipe and prewarms the intake air in the outer pipe. Some other type of heat exchanger system may also be used.
The exhaust is also cooled so that at the exit the exhaust is composed of primarily water vapor and carbon dioxide. These components become acidic and must be properly managed. Because of the acidic nature of the exhaust the exit piping used is typically PVC and run through the sidewall of the house. Venting through the roof can be problematic and cause damage to roofing, especially metal parts.
