Q. We need your valuable advice: Is it a good idea to close central air-conditioning vents in unused rooms? We have a guest room, little used bathroom, and small laundry room where we keep the vents shut to save on electricity. What is your recommendation on this issue?

A. If the rooms are not used normally, shut the vents and the doors, and you will be saving a little. Doors and vents will be easy to reopen when necessary. Some critics may say it unbalances the system, but a well designed system can improve with some outlets shut off.

Q. A friend marbleized her house, marble tile all over. Now, she has a small leak and wants to know if they have to break up the marble to get to the leak.

A. Not necessarily. There is a national franchise called Roto-Rooter, which inspects pipes for leaks and blockages, which it can cut out with a blade. Sometimes, but not always, it may have to break into a wall to get at a broken pipe. Have your friend give Roto-Rooter a call.

Q.I read your column about cooling with fans, so I put a fan in each room, and I still am not cooling off. How come?

A. I might have neglected to explain that fans cool if there is cool air around. For example, when it is cooler outdoors than in, then fans will bring in that cool air and exhaust warmer air. This happens in northern climes when the weather cools in the morning. When it warms up in the afternoon, shut them off.

 In the South, it often doesn’t cool off for days and nights, making cooling harder without an air conditioner.

Q. My 1967 house has equally old Andersen double-glazed windows that still work well, but a lot of the nylon strings have broken which makes them hard to open and stay open. Who can fix them?

A. Although they are out of warranty, it won’t hurt to call an Andersen store or dealer. He might say they don’t make them anymore, but it is worth a call. If unsuccessful, call a specialist, in the Yellow Pages under Windows, Repair and Parts, or something similar.

Q. I installed a good, big exhaust fan in my small (6 by 6 feet) bathroom, with the outlet pipe through the ceiling and going about 10 feet on the attic floor to an outlet in the gable wall. But when I run it during showers and afterward, it doesn’t clear the room. Much of the moisture stays on the back of the shower curtain, and sometimes condenses on my bedroom skylight. What’s wrong? Is the fan too powerful? It has one speed.

A. You are not giving the fan enough air to push out, and with the bathroom door and window closed, it is laboring. So, open the door and possibly the window just a bit so the fan can clear the air. You can open the skylight just a crack to prevent the condensation.

Q. I cut down seven overgrown lilac bushes, and was able to pull one stump out by hand, but six stumps about a foot high remain. They are such a hazard that I put a fence around them. How can I get them out?

A. Many ways, none easy. 1) Spend the summer digging them out bodily, cutting roots until they pull out. 2) Cut them at ground level and cover them with piles of cow manure mixed with earth. They will rot out in about two years. 3) Have a landscaper dig them out. 4) Have a stump grinder, a huge loud machine, do the job in minutes.

Q. I have a bit of leftover paint from a project, and it is water-based acrylic, somewhat congealed, but not hard. It’s in a glass jar, so I can’t take it to a paint store to reshake it. How can I restore it so I can use it?

A. Stir like crazy. Not fast but steady. If the paint begins to blend into itself, and is the same color along the paddle, keep stirring until it is a fully even color. Then you can use it. If it is hard to stir, add a thimble of water and try again. If nothing seems to work, the heck with it. It must be disposed of as a hazardous substance.

Q. A man built a real stairway in the sunroom of my summer house, going to an upstairs room once used for sleeping. He ruined the sunroom. I can take that stairway down, but what can I do to gain access to it? It will be used for storage.

A. You can build a ladder leading to a trap door in the ceiling. The vertical ladder can be permanently attached to the wall or stored elsewhere.