To trace odor, ducts a good place to start

The Inspector's Eye

October 28, 2001|By Dean Uhler

Karen Watson of Baltimore moved into a renovated rowhouse and complains that she can smell a basement odor in the living room.

She is concerned that the ventilation system installed during the rehab may be causing the smell, partly because she noticed that part of the ductwork in her unfinished basement uses the ceiling and beams, which are weathered and partly moldy.

One question is whether the ductwork described is proper, and another is whether it is causing the smell.

First, assuming the ventilation system referred to is the heating and air conditioning system, it is acceptable to use parts of the interior framing - floor joists, subflooring, wall studs, etc. - as ductwork for "return air," but not for supply air.

Return air is air drawn into the system through vents inside the house and conveyed to the furnace or central air conditioner. After being heated or cooled, that air becomes supply air and is distributed to rooms through supply ducts. Building codes allow return ducts to be constructed using interior framing. Supply ducts cannot use interior framing.

Check the duct in question to see which type it is, return or supply. Floor joists are the parallel boards that are overhead in the basement and support the floor above. Return ducts made from floor joists are created by covering the space between two adjacent joists with sheet metal. The edges of the sheet metal are fastened to the bottom of the joists, creating a "panned-in" duct between the joists.

To determine whether your panned-in ducts are return or supply ducts, turn up the heat and let the system warm up for a few minutes. After warm air is coming out of the vents, go down in the basement and feel the sheet metal on the panned-in duct. It should be room temperature. If the sheet metal is very warm, the panned-in duct is an improper supply duct and should be replaced.

Now for the cause of the smell. If the wood in the ductwork is moldy, it should not have been used in the duct, and replacement of the duct is advisable. But wood in a return duct is usually bone dry and, therefore, not very smelly. So, while it is possible that old wood in the ductwork is contributing to the smell in the living room, other causes may be more likely.

If air enters or leaves the heating and air conditioning system in the basement, it can cause the whole house to smell like the basement. For example, air drawn into the system through a return vent located in the basement - or through air leaks in the return ducts or furnace cabinet - will be distributed throughout the house with the heated or cooled air.

Conversely, leaks from supply ducts in the basement can pressurize the basement, forcing air to migrate from the basement to the first floor. Either way, the musty smell in the basement makes its way upstairs.

Look for a return vent in the basement. If there is one, you may want to eliminate it, but don't just close it off. The vent may be necessary to provide adequate air flow, especially for the air conditioner. Consult a heating contractor, who can boost return air flow from upstairs if required when the basement return vent is closed off.

Check the ductwork in the basement for air leaks. Installation standards require joints in ducts to be made airtight by means of tape, mastic or gaskets.

Panned-in ducts, for example, are often leaky because of unsealed joints in the wood and holes drilled in the joists to run pipes and wires. You can look for leaks in ducts and seal them yourself, but consider hiring a heating contractor to evaluate your ductwork.

Finally, if you don't have a dehumidifier in the basement, consider getting one. Keeping the air dry will minimize the musty smell there and elsewhere.

Inspector's Eye

Dean Uhler has been a home inspector for more than 12 years and is president of Baltimore-based Boswell Building Surveys Inc. Uhler is a member of the American Society of Home Inspectors (ASHI) and is the treasurer of the Greater Baltimore Chapter of ASHI.

Questions, with name, address and daytime telephone number, about homes and home inspections can be faxed to 410-783-2517, e-mailed to or mailed to Inspector's Eye, Second Floor, 501 N. Calvert St., Baltimore, Md. 21278-0001.

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