ShareThisQ: I am thinking about replacing the ducting in my house and adding a zoning system. I have spoken with several contractors and have received differing opinions and ridiculously different prices. Can you help me figure out what I need?A. When installing ducts to handle conditioned (warmed or cooled) air, several factors need to be considered. The calculations required to arrive at an efficient system can often drive an engineer up a wall.Just a few things that need to be considered when designing a supply-and-return duct system are:-- Cubic footage of the area to be conditioned-- Amount of insulation the home has and how much air infiltration is expected-- Average daily temperatures-- The distance from the fan system to the most distant room-- How many levels are to be conditioned?A one-story house with the fan system located in the basement has to be considered a two-story structure.-- What is the cubic feet per minute of the fan, and is the fan a single-stage or a multi-stage fan?-- What are the expected humidity levels that need to be controlled?It is not a simple matter of guessing or using a rule-of-thumb system when designing an energy-efficient system. After all the calculations are complete, a zoned system is often used to establish different comfort levels to different areas of the home using a single-fan system. Each zoned area has a thermostat attached to a control computer for the fan system, so that, for example, you can set the bedrooms to one temperature and the living areas to another temperature.Larger homes or homes with multiple levels can have as many as four zones on one system, but you cannot set one thermostat to heating and another to cooling. You can only adjust the temperature.The computer prevents the system from operating on both the heating and the cooling cycle at the same time.It is impossible to select the proper system without measuring and calculating your needs.However, there are a few things you must insist on being done when new ducts are installed. The ducts must be sealed airtight at all joints and seams and at all cutouts for registers. Leaky ducts are inefficient, even if the fan system is inside the home.Return ducts must also be sealed airtight at all joints and seams and where the wall cavities are to be used as part of the return system.If possible, the drywall needs to be sealed to the wall studs at the return cavities. Also caulk and seal any openings where electrical cables or plumbing pipes pass through the studs at the return cavity.(Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home-improvement questions at C. Dwight Barnett, Evansville Courier & Press, P.O. Box 286, Evansville, Ind. 47702 or e-mail him at d.Barnett(at)insightbb.com.)
What to consider when designing a zoned duct system
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