Preventing Frost Buildup On Sewer/Septic Tank Roof Top Vent Stacks


This is an email I received from one of my readers. “I’ve 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 shouldn’t be climbing on the roof to clean these out (about once every one or two months) in the winter. Is Sweetfilter Odor Eliminator 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. 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 roof damage. We want the roof to be as cool as possible. You should insulate the vent pipe stack in the attic if it sticks above the attic floor insulation. Then install a Sweetfilter Odor Eliminator on the outside roof stacks. Most plumbing and building codes specify 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 6 to 8 inches above the roofline it needs to be wrapped with insulation in the winter. If the temperature of the vent stack pipe in the attic is below freezing it must be insulated; otherwise the Sweetfilter Odor Eliminator will not work. If the house temperature is below 52 degrees Fahrenheit the Sweetfilter Odor Eliminator will not work.

Sweetfilter Odor Eliminator filter is designed to insulate the stack inside it with the equivalent of 1 inch of air insulation. I would not worry about the Sweetfilter Odor Eliminator on any roof vent stack if the steps above were followed. Sweetfilter is the only company with filters on vent stacks in schools in Alaska.

Joe Kessler

Pennington Equipment Company – Products, Information, & Online Ordering

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