Q. I have a forced-air condensing furnace/air-conditioning unit in my uninsulated attic. This winter the condensate pipes froze and upset the furnace operation. I could install heat tape to keep the pipes from freezing, but I also lose a lot of heat via the frame, ducts, and leaks. Does it make sense to build an insulated enclosure (i.e., small room) around the unit? Would there be code issues? The furnace runs on propane and has a vertical PVC flue pipe. Also, the rafters are within a few inches of the side of the furnace, and the vented roof peak is about 3 feet above.
D. URBAN, Ashburnham
A. Heat tape would be the simplest solution, or you could install a continuous-circulation loop pump and temperature thermostat on those pipes to keep the water moving. I’ve built a room like this for a client before, and before we did it we checked with the HVAC company. Assuming your HVAC contractor gives you the green light, I see no reason why you cannot enclose the vulnerable pipes and unit into a conditioned, heated space.
Air flow and clearance issues must be addressed. You must provide combustion fresh-air supply vents for a furnace, unless the system has a fresh-air supply pipe. Today most 90 percent-efficient furnaces have air intake and exhaust pipes feeding the furnace and have a zero or 1-inch clearance rating, meaning you can build a wall next to them.
I would encase the furnace in an insulated mechanical room in the attic if I could. Not only would I make the utility room large enough for proper furnace clearances, it would be big enough to allow access to service the furnace and change the filters.Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to firstname.lastname@example.org or tweet them to @robertrobillard.