Where the best place to put the furnace?
Q. Maybe you can help settle a disagreement between me and my wife. We were looking at model homes and I noticed one of the models we liked had the furnace in the garage and another model had the furnace in the laundry room. I like to tinker and I need all the room in the garage I can get, but the one in the laundry room makes it a little cramped in there for hanging laundry. What's the difference?
A. There is a big difference as to where a furnace is located. Furnace installations are naturally leaky unless properly sealed — that is, they can leak a lot of air through the furnace's cabinet and at the sheet metal added to the furnace. The added sheet metal would be the supply ducts and the cold-air return ducts. If the ducts and the furnace are in a garage, attic or crawl space, they are, in essence, located outside and you will lose heated air in winter and gain heated air in summer.
No matter where the furnace is located, you will find that in most homes a majority of the ducts are outside in an attic or a crawl space and a lot of energy is lost through the placement of leaky ducts. There are exceptions, such as when a furnace and all the ductwork are in a basement, which is heated and cooled, or in some of the concrete-slab homes with the ducts under the slab.
When a gas- or oil-fired furnace is inside, in this case in a laundry, you have to be concerned with the amount of air available for combustion. A small laundry room with a water heater and a dryer would be competing for the same amount of air if all the appliances were on at the same time.
A 10-foot-square laundry room with an 8-foot ceiling would have 800 cubic feet of air available for combustion. A 100,000 BTU (British thermal unit) furnace next to a 40,000 BTU water heater would require approximately 1,540 cubic feet of air per hour for combustion even without the dryer pulling air out of the room. In this case, there would not be enough air for all the appliances.
Most modern furnaces have a fresh-air intake pipe to supply the furnace with combustion air from outside, or the laundry room may have a louvered door to supply makeup air from the rest of the house. If there is not enough combustion air, deadly carbon monoxide gas can develop.
If you are buying a new house, you now know what to look for. If you have an existing home, you can seal the ducts at every joint and seam you can find using metallic tape and silicon caulking. Ducts in a garage, attic or crawl space can then be wrapped with foil-faced insulation designed especially for ductwork.
The insulation should be rated at R-6 to R-8 or higher depending on local requirements. The higher the R-rating, the more resistance to thermal transfer you have. Insulate the exposed water lines if the water heater is in a garage and insulate the larger of the two pipes for the air-conditioning system where they are exposed both outside and inside. It would also be energy-wise to insulate the garage walls and ceiling and try to keep the overhead door closed except when entering or exiting.
• Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home improvement questions at d.Barnett@insightbb.com.
Scripps Howard News Service
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