Why do heat pipes run through cold garage?

Q. I am currently not using the two bedrooms over my unheated garage. Since they're on a separate heat zone (hot water baseboard), I'm considering having that loop of pipe drained at the time I have the annual furnace maintenance performed and not heating those bedrooms at all this winter. A friend warned me that doing so could cause dampness and mildew problems in the unheated rooms, and it wouldn't be worth the potential savings on my energy bill. I do get water in the garage after heavy rains, so this is a concern. What is your opinion?

Also, I think the layout of the pipes supplying those bedrooms is nonsensical: Copper pipe runs some 20 feet through the unheated garage then up into the bedrooms for about 18 feet of copper-fin baseboard, then back down into the garage for an L-shaped run back to the starting point. Altogether, there is about twice as much pipe in the garage as there is baseboard upstairs, and during cold snaps, those bedrooms stay cold for days.

I think the once-and-for-all solution would be to have a plumber reroute the pipes to change the out-and-back runs through the garage to actual useful baseboard in the bedrooms.

A plumber friend was concerned that this might overheat the bedrooms or affect the furnace's cycling. Since this is its own heat zone, and it's only maybe 30 percent of the heated square footage of the home, I don't think either of those concerns is likely to become a problem, but I have no experience in this area.

Finally, I just ripped all the fiberglass insulation out of this garage (between the bedrooms' floor joists and on the wall facing the basement) because various areas of it were falling down, mildewed or there was evidence of past rodent infestation, plus all of the vapor barriers were on the cold side (i.e. facing the garage). How important is it that I replace this insulation, and is there any insulation that won't be inviting for invading vermin?

A. Although it makes sense to drain the unused lines from a heating standpoint, it may cause unwelcome consequences in the two bedrooms, as your friend warned. Extended periods of no heat are likely to cause mildew and damage furniture.

The layout of the pipes may have been the easiest way to get heat to these two rooms when the house was built. It is difficult to question the judgment of the contractor without studying the entire heating layout, but it does seem unusual to have so many feet of feed and return in an unheated garage.

Your concern is valid, and you may want to have a heating contractor survey the system and tell you if the pipe layout can be changed at a reasonable price. It may involve tearing into walls to rerun the pipes. If the pipe runs through the garage are not insulated, they should be.

There is no concern about the rooms overheating or the boiler's cycling being affected; the heat in these rooms is controlled by its own thermostat.

You should replace the insulation in the garage ceiling and the wall facing the basement. If the fire code drywall that should be applied on these surfaces is well done, there should not be rodent infestation. You can use fiberglass or, better, dense-pack cellulose, which is treated against vermin problems.

Q. I have an old (25 plus years) asphalt driveway that has moss and lichen growing on it. My power washer takes the moss off without much effort but misses the lichen. How can I get the lichen off, or can I seal over it?

A. The lichen should be removed. If the infestation is not extensive, a steel brush should loosen it up so your power washer can get rid of it. You can also use a floor scraper (a tool with a flat steel blade on a long handle used to peel off resilient flooring).

Q. I have a building with aluminum siding that was installed in 1965. It is in excellent shape, but the white coloring is dull, has occasional dark stains from mold or adjacent oak trees, etc. There is a white powdery dust that rubs off when wiped with a finger. Can it be painted? With what kind of paint? Does it need primer? If so, what kind? How do I prep it for painting?

A. The white chalk is a built-in process to keep the aluminum clean. But after nearly 45 years, it is time to refresh the paint. Pressure-wash the siding with a solution made of TSPPF and fresh Clorox bleach to clean it of the chalk and other pollutants. Then paint the siding with a quality exterior latex paint or one made especially for metal.

Q. I lost the column that mentions a cleaner for wood kitchen cabinets. Can you send me the name of the product that you mentioned?

A. The miracle cleaner is Milsek. You can buy it online at milsek.com.

• Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. Write to him in care of the Daily Herald, P.O. Box 280, Arlington Heights, IL 60006, or via e-mail at henridemarne@gmavt.net.

© 2009, United Feature Syndicate Inc.