Preventing Frost Buildup On Sewer-Septic Tank Rooftop Vent Stacks-Stinkpipes

This is how to prevent frost buildup on your sewer vent pipe so you can install an odor eliminator.

This is an email I received from one of my readers. “I have read a few articles by you on the internet regarding septic issues. We live in Askov, Minnesota (near Duluth) and experience frost build up in our vent stacks. My husband and I are older and really should not be climbing on the roof to clean these out (about once every one or two months) in the winter. Are Odor Eliminator filter caps appropriate for use in Minnesota? Will they prevent the frost build up? Thanks in advance for your help.”

This started some serious thinking since I was not aware that in the far North stack vent pipes could frost shut blocking the vent. We all know if the vent is blocked the toilet will flush but the waste will not flow down the drain, in fact no drain in the building will work. That is why it is against all building and plumbing codes to install any valve in a rooftop sewer/septic tank vent stack.

In most new homes or buildings we insulate only the attic floor which is on top of the ceiling in any home or building. Some designs only have a crawl space below the roof. The roof itself is only insulated in a totally sealed building today.

We go to great lengths in design today to keep warmth away from the actual roof plywood and shingles to present the thawing/freezing cycles that cause ice dams and resulting roof damage. So we want the roof to be as cool as possible. You should insulate the vent stack in the attic between the attic floor and attic roof and then put an odor eliminator filter on the outside stacks. There then should be roughly 6″ to 8″ of stack sticking out of the roof on the outside.

The inside temperature of all vents in the house is the same temperature as the rest of the house. The air temperature in septic tanks is the same as the ground that surrounds them. The ground temperature in North America is 52 degrees year round above the freeze line which is about 2 to 4 feet down in the earth depending on your area.

If the vent stack is more than a few inches above the roof line it needs to be wrapped with insulation in the winter. If the temperature of the vent stack pipe in the attic is below freezing the odor eliminator filter will not work, it must be insulated. If the house temperature is below 52 degrees Fahrenheit the odor eliminator filter will not work.

Some odor eliminator filter designs insulate the stack inside it with the equivalent of 1 inch of air insulation. I would not worry about the odor eliminator filter if the conditions are correct. I know of one company who has them on vent stacks in schools in Alaska.