Jim Rooney On The Level

Q. I have a old house that I bought that has aluminum siding on it that I may need to replace since it has dents, been painted and may need to make a sliding glass door into a window. The house was built in 1983. In replacing the siding, I was wondering what type you recommend and also since the siding would be off, should I also do a wrap of the house or consider siding with some time of insulation. I have noticed a lot of homes that appear to have mold or mildew appearing on the siding. What causes this and when purchasing new siding is there something that I should consider so this doesn't happen to me?

A. Your house is breathing air down the fireplace flue and you probably notice it more after a rain-- especially a warm summer rain-- because the air migrating into the house via the chimney is humid. The moist air picks up the odor of creosote that has been deposited on the sides of your terra-cotta chimney flue liners as a product of burning firewood and wafts it into the house where you smell it. Chimney cleaning will help a little but wont eliminate the problem.

Air is almost always moving one way or the other up or down your chimney flue in response to pressure changes from inside of the house to the outside. Your house is aerodynamically connected to the exterior via the chimney. The problem can be attributed to modern, almost air-tight construction methods that energy conscious building techniques have encouraged, along with things in our homes that tend to lower or de-pressurize the inside of our homes by their use such as clothes dyers, bath fans, kitchen fans-- even attic fans-- that pull air from the inside of the building and exhaust it to the outside. If you remove air from an enclosed space it lowers the air pressure of that space relative to all the air around it. Air wants to equalize itself so it draws make-up air, as it’s called, from wherever it can. In your case it’s coming down the chimney. Mere millebars of air pressure differential will get air moving from one direction to another.

Understanding the cause of the problem can put you on the path to solution but it’s not so easy in this case. You’re pitting chimney caps and old-fashioned flue dampers against a modern building structure. They can’t solve the problem because they were really never meant as a true air-tight seal. Some spring-loaded chimney top dampers that are well gasketed can do the trick. They cost about $350. or more depending upon the height of the chimney.

Sealing the chimney with a masonry sealer to keep water out of the brick isn’t really getting at the root cause and, by the way, if you get sloppy applying some of these sealers and splash some on your roofing near the chimney you’ll be dismayed to watch patches of your asphalt shingles dissolve.

Trying to be careful while operating exhaust fans by balancing the air through cracking a window open a bit during operation might help so give it a try and see if that makes any difference. I’ve seen folks place candles in the fireplace and light them to try to reverse the air flow through convective air movement from the candle flame. That looks nice. I once received a tip from a lady who said she places a dish of apple cider vinegar in the fireplace and that does the trick. I don’t know that for sure but I have heard from others who say this has merit and the price is right.

Fireplaces inside of modern homes are a total anachronism and just don’t make sense. However, you’re not going to easily get rid of something that appeals to some deep, almost primordial comfort and safety gene lodged deep in our brains that loves the look and warmth of a dancing flame on a cold winter’s eve. Someday-- in the far distant future-- houses will be routinely equipped with barometrically controlled air-to air heat exchangers to keep the relative air pressures balanced all the time while bringing fresh air in. Then fireplace flues acting as an air intake will no longer be an issue. The technology is here-- it’s currently about a $1000. I’ve seen it done and it works.

Keep the mail coming. If you've got a question, tip, or comment let me know. Write "On The Level," c/o The Capital, P.O. Box 3407, Annapolis, MD 21403 or e-mail me at jimrooney@jimrooneyonthelevel.com or inspektor@aol.com.