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Kitchen exhaust is best vented downward

Q. I have a stove vent that drips water when it gets cold out. It is angled up, is about 20 feet long and vents through the roof. I assume warm air rises into the vent pipe and condenses, causing the dripping. Is it best to vent this through a soffit, making the vent lay along the attic floor? I added insulation on top and along both sides of the vent pipe, but that hasn't helped. We want to replace the stove fan/vent, but need a suggestion to fix this before purchasing a unit.

A. I assume you are referring to a kitchen stove. Any vent rising in a cold attic is likely to have condensate drip back down, wet insulation and damage ceiling finishes. It can also lead to rusting of the fan.

No venting of bathroom or kitchen fans should terminate at a soffit or gable vent. These are intake points for attic ventilation, and any discharge through them is redirected back into the attic.

Bathroom and kitchen vents should be terminated through walls. On the first floor of two-story buildings, the termination should be through the band joist between floors. On the first floor of one-story buildings or the top floor of a multistory building, the venting should be through a duct laid flat and terminating through a gable wall.

The duct is best insulated if possible by snugging R-13 fiberglass batts on each side and laying another set of batts on top of the duct.

The above recommendations are based on the majority of situations in houses. The very best way to vent bathroom and kitchen fans is downward. This is easy to do when building a new house, but likely to be difficult in any retrofit situation.

Bathroom fans can exhaust through a band joist in a basement or crawl space. A kitchen fan is also best vented downward, as exemplified by Jenn-Air stoves.

Venting downward respects the laws of nature. All buildings are subject to stack losses - warm air rises and exfiltrates through any cracks and crevices it finds, creating a negative pressure, which causes infiltration through similar avenues on the lower parts of the building.

Vents rising upward are excellent exfiltration paths, which exacerbate the problem, while the flap on low terminations is firmly sealed because the stack effect wants to suck in makeup air through these openings.

Q. Several homes here in Holden (Massachusetts), including my daughter's, are besieged by woodpeckers tap-tap-tapping at the sides of their houses. My daughter has had to have clapboards replaced as a result. Do you know of any way to handle this menace?

A. If the woodpeckers are tapping to mark their territory, I do not know of a way to stop them inexpensively. Your daughter may want to look at Bird-X Woodpecker PRO, a pricey electronic repellent at $280, www.bird-x.com, click on Bird Products and on Sonic Bird Control. If it does work as advertised, it may be worth the price to her.

A reader mentioned to me that he/she hung metallic foil, but it didn't last long in the wind. If the woodpeckers are looking for insects seeking shelter from the winter in the clapboards, your daughter may want to try a system given to me by my longtime entomologist friend that has worked quite well. I hang rendered suet cakes nearby. Rendered suet cakes, available in hardware and agricultural stores, are not affected by higher temperatures and do not become sour. We keep the wire cage filled year around. They are highly successful, and we enjoy watching downies, hairies, and occasionally we have seen a pileated woodpecker come for a feast. Other birds are there all the time as well.

I bought a double cake size suet cage, but learned quickly that I should only put one cake in it at a time. When I started hanging it, I put two cakes in and witnessed their quick disappearance. Crows could access them from the top of the cage and literally liberated huge chunks at a time. So now I use only one cake, which lies on the bottom of the cage, and since the crows are unable to hang upside down, the suet is preserved for the smaller birds.

Q. I had a problem with my bathroom fan vented in the soffit. I had mold growing on the roof sheathing starting from the end of the exhaust tube. I changed the exhaust to exactly what you recommended: PVC bell-end drainage pipes to an aluminum hooded jack with a flap. The pipe is wrapped in 4-inch insulation. The problem I have is during our latest cold snap, where temperatures got down to 0 degrees, the flap froze shut from the exhaust moisture in the bathroom leaving through the hooded jack. With the fan on, it took about three minutes for the flap to heat up and open. Any suggestions?

A. Often, solving one serious problem may lead to experiencing another one - hopefully minor in scope. You have found the solution: Sending warm air through the insulated duct eventually melts the frozen flap.

I am sorry to say that, although you have done it right, I do not know of a better way to prevent the freezing of the flap. You could try spraying WD-40 on the edges of the flap; it may work.

One of the suggestions I have made in the past is to try to vent the fan on the south side of the house, if possible, to allow the sun to melt the frost.

Q. Regarding venting a bathroom vent to a wall and not the attic, my bathroom does not have an outside wall to vent to, since there are other rooms surrounding it. What should I do? My bath badly needs a vent as the paint is starting to bubble and I do see mold on the ceiling in the shower area. My bathroom is 5-by-11 feet and I would like a fan/light combination.

Additionally, my basement bathroom has no vent and the concrete is starting to disintegrate. There is a shower, toilet and sink. There is a drop ceiling and the metal is rusting, the linoleum is lifting and it looks awful. The bath is next to the garage space and is surrounded by other interior rooms. What can I do about installing a vent in this situation?

A. Most bathroom venting is done through the ceiling and not directly through an exterior wall in the bathroom itself.

If your bathroom is just below the attic, a ceiling fan/light combination should be installed by a licensed electrician in the most logical place. The venting is done in the attic as I have often described: A flat run on top of the ceiling joists to a gable wall, using a Schedule 20 bell-end drain pipe. The bell end must face the fan and, if possible, the pipe should be slightly sloping toward the outside by placing two small blocks of wood of diminishing size under each section of pipe. Place 4-inch-thick fiberglass insulation batts snugly on the sides and top of the pipe.

Terminate the run outside with a hooded metal or plastic jack with a flap. Avoid louvered jacks, as I have seen too many with a missing flap, which is a way for vermin or birds to enter the duct.

For your basement bathroom, a fan should be installed in the drop ceiling and the duct fed to a band joist between two joists. If the only way to vent the fan is through the garage, the duct should be extended to the outside wall of the garage and not terminate in the garage itself.

Q. I read your answer about venting the bathroom from attic to outside in our local paper. Our full bath is also vented to the attic and has been for 35 years. We do not have a mold problem. Is there any reason we should change to vent to the outside if it hasn't caused a problem so far?

A. Although your installation is not right and would normally cause problems, perhaps you have extraordinary attic ventilation or you do not use the fan often enough to cause a problem. As the old saying goes: "If it ain't broke, don't fix it."

Helpful suggestion: "In today's Daily Herald, a question was featured that asked for help in getting rid of Asian lady beetles. I strongly recommend the following product, which has proved very successful in ridding the south side of our house of box elder bugs: www.buggslayer.com.

"I read your column every week and have learned many helpful hints. This is just my way of 'paying it forward.' "

A. If it also works on Asian lady beetles, this is a great suggestion. Thank you.

Another great tip from a reader: "Henri, for small cracks in concrete, try putting a clear silicone caulk into the crack. Then wipe the excess off with a damp finger. Let it set for a minute or so and then sprinkle dry vinyl cement mix on top while the caulk is still wet. Press the cement mix into the caulk with a light touch. Let it stand there for a few days then broom the area. This makes it almost invisible and caulk has the ability to expand and contract with weather changes better than the cement mix. This will work great with cracks up to one-quarter inch. Hope you like this idea. It works great for me here in Chicago weather.

A. Great suggestion. Thank you. If the occasion presents itself, I'll try it.

• Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. His book, "About the House," is available at www.upperaccess.com and in bookstores. His website is www.henridemarne.com. Readers can send questions to Henri de Marne's email address at henridemarne@gmavt.net, or to First Aid for the Ailing House, Universal Uclick, 1130 Walnut St., Kansas City, MO 64106.

© 2014, United Feature Syndicate Inc.

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