Q. The heating ducts in our basement are exposed, and I know a lot of heat that I’d like to have upstairs is being lost moving through the ducts. The main duct is large and rectangular and runs almost the full length of the basement. Can I insulate the ducts? Should I tape the joints first with duct tape?
A. You can insulate the exposed ducts, but keep in mind that the heat they are putting into the basement might be keeping your water pipes from freezing in very cold weather. If you live in a cold-climate region and have been getting sub-freezing temperatures, you might want to consider carefully before insulating.
If you decide to go ahead, you should tape the joints first, or you can send more heat to the registers just by taping. However, so-called duct tape is a poor choice for this task; duct tape has many uses but sealing ducts isn’t one of them. If used on heating-air conditioning ducts, this misnamed tape will often come loose because it can’t hold up under the temperature changes. Some tapes used for effective duct sealing have a metallic coating and many pros use a caulk-like material called mastic.
If you decide to seal and insulate the ducts, a good strategy is to install one or more adjustable registers in the big main duct. Then, after you insulate, you can use the registers to deliver some heat into the basement when you want it, or shut off the heat. I assume the basement ceiling (the floors of the rooms above) is not covered or insulated. Some of the heat generated in the basement will rise to the rooms above and help keep the floors warm. If you have water pipes near windows, it would be wise to insulate them. Insulation for various sizes of pipes is available at home centers, and is easy to install. Usually, it is made of foam plastic and has a locking split down the side so it can easily be slipped over the pipe and fastened in place. Don’t depend on this insulation to protect pipes running near windows in very cold weather, though.
Some heat in the basement will probably still be needed to prevent a possible freeze-up. One well-known strategy is to let a faucet dribble a little; running water doesn’t freeze as easily as standing water.
Keep in mind that a very small pipe leak can cause significant damage if undetected. In case a leak starts, keep a repair kit on hand to fix it until a permanent repair can be made. Most emergency repair kits don’t require soldering or cutting of the pipe. I have one that simply clamps around the pipe at the point of the leak and is held in place with screws. In some cases, very tiny leaks can be stopped or at least slowed down by wrapping them tightly with vinyl electrical tape. Taping is definitely only a temporary repair and a better solution should be found as soon as possible. If a severe leak occurs, shut off the water at the main valve and call either your water supplier or a plumber.