Design & DIY

Cottage Q&A: Insulating a septic tank

A black septic tank in a sand bed By Gozzoli/Shutterstock

Our lot is primarily bedrock, so as a result, our septic tank is above ground. I have built insulated walls and a roof for it. What would be the best heat source to prevent it from freezing in the -30°C winters?—Going Above and Beyond

You’re smart to keep your septic tank warm. If not, the natural processes that allow for the treatment of the effluent won’t happen—at least not as efficiently. “Sewage doesn’t like to be cold,” says Sandy Bos, the on-site system inspector for Ontario’s Township of Muskoka Lakes. “Sewage wants to be as warm as possible.” Word.

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If the tank is polyethylene, wrapping some kind of heating cable around it could work. But it’s not a viable solution if the tank is concrete, says Lorne Heise, the president and CEO of Heat-Line. “Applying heat tracing from the outside is very difficult in that case. And you’d require a large amount of energy.” There are septic-tank-specific heating options out there: Heat-Line sells tubular heaters that go right into the tank; the U.S.-based Septic Heater Company makes units that blow warm air into the tank.

But, hang on: adding a heat source may not be necessary, especially if you’re going to be using the septic system through the winter. “Waste water itself is a heat source,” says John Rowse of the BC OnSite Sewage Association. “It’s about 15°C to 19°C when it enters the tank.” As bacteria work to break down the waste, “they generate their own heat. Even the waste in the tank is ambient, about 10°C to 15°C,” he explains.

Still, 30 below is scary cold. If you’re concerned, “you just need to insulate the heck out of the tank,” says Bos. This is as simple and cheap as putting a couple of layers of two-inch foam insulation on the top and around the sides.

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This article was originally published in the Winter 2016 issue of Cottage Life.

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