Q. We made the plunge and installed multi-zone mini-splits in all the rooms of our 1950 ranch. We have shut down our oil furnace but not drained our baseboard heaters. The basement, all below grade, has blown insulation in the ceiling. We do have pipes, both baseboard and potable water, near external walls. In 33 years, this basement has never gotten colder than 50 degrees or so. Without the furnace running and acting as a heat source, how much should we worry about freezing pipes? Should we get temperature warning alarms and pipe heaters or leave the furnace running? Thanks.
A. Typically, an unheated basement will stay between 50 and 55 degrees, assuming there are no gaps to the outside. Most frozen pipes happen when they are inside the exterior walls above the basement, not in the basement. What I would recommend with the blown-in insulation in the floor bays above is to insulate the perimeter of the basement where the foundation meets the framing. Most basement air leaks happen here. We like to use closed-cell icynene, but given the small size of the project, this may not be practical. An easy alternative is to use 2-inch rigid insulation cut into the floor bays against the exterior and spray foam around the perimeter, sealing all the gaps. This is very effective at air sealing a basement.
Pipe heaters are a Band-Aid on a problem that should be solved properly. There are inexpensive alarm systems that can send phone alerts if the temperature in the basement gets below 32. Users can tie it into their phones. Again, any basement that gets to 32 degrees has serious issues with infiltration. Since you appear to be trying to lower your carbon footprint, properly sealing the basement space is an important step. You could try the alarm for the first year as a safety precaution.
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