If you’ve ever warmed your toes with a hot-water bottle, you know the principle behind Michael Salter’s cottage heating system. Except this “bottle” holds 4,500 litres, it’s way too big to fill from a kettle, and you’ll never fit it beneath the covers.
The heart of Michael’s system is a water-filled tank from Brooklin Concrete, snuggled in foam insulation in the basement of Michael’s Lake of Bays, Ont., cottage. At 11 p.m. on winter nights, when Ontario’s 2.8 cents per kilowatt-hour “Ultra-Low Overnight” electricity rate kicks in, an electric boiler warms the water in the tank to a balmy 65°C. When rates more than triple at 7 a.m., the boiler shuts down. For the rest of the day, the tank sends its stored warmth to the cottage’s hydronic in-floor heating.
“I came up with the idea and was researching it, but I couldn’t find anyone doing it,” says Michael, a former aircraft engineer who clearly enjoys a technical challenge. He began assembling the system when he built the cottage in 2011, starting with the tank and a propane boiler. When cheaper electricity became available, he added a second-hand electric boiler, relegating propane to a backup role.
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Because the tank is strictly a storage reservoir for hot water—the boiler and the hydronic heating operate on their own separate plumbing loops—Michael uses car radiators (one salvaged from a vintage Austin Mini) to act as heat exchangers, transferring heat energy from the boilers to the tank, and from the tank to the hydronic system. The tank, plumbing, boilers, and exchangers took about “$2,500, plus many hours of my time—most of that on research,” he says, suggesting an electric immersion heater or solar energy may work for cottagers who don’t go the boiler route.
Now, on winter weekends, Michael fires a woodstove for cheery cottage heat, “but when we’re not there we keep the cottage from freezing entirely by electricity,” he adds. The savings are heart-warming. “To keep the cottage at eight to ten degrees Celsius costs about
$30 in electricity a month, compared to the more than $200 I was paying for propane.”
This article was originally published in the Winter 2024 issue of Cottage Life.
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