Best Way Patch Hole From Wall Heater

QUESTION: I recently installed a central heating system in my home. The old heaters, measuring 20 by 60 inches, are mounted back-to-back in the wall between rooms. Removing these units will leave a huge pass-through between rooms. I want to frame out the openings and repair the walls so the patch won’t be noticeable. Should I use lath and plaster, or should I try to make a flush patch with easier-to-handle wallboard?

ANSWER: If you want a perfectly smooth wall, you should cover the entire wall--from corner to corner--with wallboard. It’s very difficult to achieve perfection with a patch. Depending on how light strikes the wall, you will see ripple shadows at the patched joints.

But if you intend to hang pictures on this wall or cover it with a textured paint or wallpaper, patching would be adequate. Because of the size of the opening, filling it with wallboard would be best.

Latex Paint Can Be Applied Over Oil-Based

Q: Please advise on the problem with a building that has two coats of oil-base paint and needs painting. I would like to change to a water-base paint. Would this idea be possible? I intend to perform this work myself.

A: According to the technical department at Benjamin Moore Paint, there is no reason that prevents you from spreading latex over oil-based paint. In fact, you can go back and forth between latex and oil. However, the wall surfaces must be properly prepared before painting.

The surfaces must be clean and free of dirt and grease spots and should not be excessively chalked. A good way to ensure proper surface preparation is to have the walls power washed. The wash water also usually contains additives to kill mildew. Priming the surface is not necessary if the surface is in good condition. That is, there are no peeling sections or blisters. If there are, those sections should be scraped and spot primed. You can then apply one coat of a good-quality house paint; two coats would be better. A good-quality paint, applied correctly, should last six to seven years.

Bigger Room Air Unit Doesn’t Mean Better

Q: My 20-year-old window-unit home air conditioner pooped out last fall, and I was told that it would not be economical to repair it. I was also told that the newer models require less power and so the reduced operating expenses would offset some of the high cost of replacement. What’s the best way of picking the best replacement?

A: If you are shopping for a new air conditioner, jot down these facts: the size of the room to be air-conditioned, how many windows it has, if it’s insulated, and the available voltage (120 or 220 volts). Also, measure the exact size of the available window opening to be sure the new machine will fit in the window.

An air conditioner’s BTU-hour rating tells you the amount of heat it can remove per hour. The larger the BTU rating, the more power it has. Remember, bigger isn’t always better. Too much capacity for the room will make it feel clammy and too little can’t cool adequately.

An air conditioner also has an energy efficient ratio. This rates the amount of cooling it does in relation to the electricity it uses. The higher the EER, the greater the efficiency.

To submit a question, write to Popular Mechanics, Reader Service Bureau, 224 W. 57th St., New York, NY 10019. The most interesting questions will be answered in a future column.