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Dripping vents in winter baffle one homeowner Controlling humidity, keeping ductwork warm might solve his problem


CHANGES in outdoor weather often produce baffling changes in indoor conditions -- things that never leaked before suddenly leak. Drafts develop in previously calm spaces. And for one reader, cold weather produces indoor rain.

"We installed a Rheem attic AC system into a typical rancher, with the vents in the ceiling," he writes. "Along with the AC we installed a fresh-air exchange system from Honeywell. The unit provides fresh air and humidity controls with an 80 percent efficiency exchange rate. At the same time, we had a ridge roof system installed (attic high-point ventilation) .

"Once we hit the cold part of the season, starting in late December, water started dripping from some of the ceiling registers. The ones that leak are fairly consistent from year to year."

The reader says both the supplier of the exchange system and the contractor who installed it and the air conditioning unit say the equipment was properly installed.

"We reviewed the AC installation, checking all ductwork and the attic unit to check for air leaks," the reader says. "We found none. We even went as far as to isolate the fresh-air exchange unit from the AC ductwork, but we still had what appears to be condensation leakage from the ceiling registers. Last winter, I sealed the vents with plastic and that did not make any difference. The last action I planned to take was to install a second layer of duct installation around the existing insulated duct.

"Have you ever heard of this happening?" asked the reader, who signed himself "Unwanted Indoor Pool LifeGuard."

We hadn't, but Steve Strain of Modern Heating and Air Conditioning in Baltimore has, and he had a couple of tips.

Condensation usually occurs when warm, moist air contacts a cold surface. Moisture will form on the cold surface and drip down. You often see it on old metal windows that are not made with insulated glass. The way to avoid condensation is to keep the warm air away from the cold surface.

Another factor in this case may be too much humidity in the air circulating through the ductwork. Strain recommended a level of around 40 percent.

Modern houses are usually well sealed, and bathing, washing dishes and clothes, and cooking create a lot of indoor humidity. Good spot ventilation can help: Be sure to run exhaust fans after taking a shower until all the steam and humidity have been blown outside. Use stove hood vents and keep dryer vents clear.

It's also possible in the reader's case that the ductwork may be getting too cold. Strain suggested that the reader make sure the air-to-air exchanger is providing some heat to the air it is recirculating. He also thought it might help to run the fan on the air conditioner to circulate air through the ducts and warm up the ductwork even in winter.

We would try the simple things first. Make sure you are in control of the humidity levels. Check the heat exchanger for proper operation. Run the fan to circulate the air and warm up the ductwork. Then, if the problem persists, consider adding additional insulation to the ductwork.

Randy Johnson is a Baltimore home-improvement contractor. Karol Menzie is a feature writer for The Sun.

If you have questions, tips or experiences to share about working on houses, e-mail us at homeworlark.net, or write to us c/o HOME WORK, The Sun, 501 N. Calvert St., Baltimore 21278. Questions of general interest will be answered in the column; comments, tips and experiences will be reported in occasional columns.

Pub Date: 11/09/97

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