Do It Yourself: Coolest way to save would be natural venting

Q. Like many others, I want to save on my cooling costs. I have been thinking of installing a powered attic fan (not a whole-house fan). A neighbor has one of them and says he is sure he is saving on his air conditioning. What do you think?

A. Most experts have concluded that powered attic fans not only do not help save cooling costs in a building, but can actually drive up the power bill and possibly have other negative effects. Unlike a whole-house fan – which pulls cool night air into a building through partly open windows and exhausts hot air through attic vents – an attic fan’s function is simply to pump overheated air out of the attic. Attic temperature can reach 140 degrees or more on hot days. The theory is that, by keeping the attic cooler, it will be easier and cheaper to cool the living area below.

I am aware that some homeowners swear that attic fans do make the house easier to cool. When I wrote a column on this subject many years ago, and reported on some negative effects of attic fans, I got several letters from fan owners telling me I was dead wrong.

So why don’t powered attic fans actually pay off, when the theory sounds so plausible? One reason is that most buildings now have well-insulated attic floors, so that lowering the air temperature in the attic has little or no effect on the living area below. Another reason is that if an attic floor isn’t well insulated, but has cracks that can admit air from the living area into the attic, the fan will simply pull expensively cooled air up into the attic and expel it through the attic vents if an air conditioner is running.

A powered attic fan can also cause backdrafting, which can pull dangerous combustion products from flame-type appliances into the living area if they are not properly vented and closed off from the fan’s suction. The cost of running the fan motor can actually increase, rather than decrease, overall energy costs. Insulated attics should have good ventilation to prevent condensation in the attic and other problems, but most experts recommend natural venting by soffit, ridge and gable vents. If powered attic ventilation is needed, solar-powered fans are usually best.

Q. I have always been told that the way to keep a lawnmower blade from turning when removing it, was to block the blade with a chunk of 2-by-4. I tried this recently and the wood kept falling out. I also skinned my knuckles when the wrench slipped. There must be a better way. Any ideas?

A. There is a better way. I had the same problem years ago when removing an old blade from a walk-behind lawnmower. Finally, I attached a large C-clamp to the rim of the blade housing so that the blade contacted the clamp when I loosened the blade bolt. With the clamp firmly in place, there were no slip-ups, no skinned knuckles, and the bolt was easy to remove. I used the same clamp to tighten the bolt when I installed a new blade.

If you are concerned about marring the blade housing with a clamp, use a couple of thin scraps of wood as buffers under the clamp jaws.

It’s a good idea to check the blades of walk-behind mowers a couple of times during the mowing season, and there are several other things to keep in mind. The blade should always be checked if the mower hits a root, hidden stump or other immovable object; a blade that is even slightly bent can damage the engine.

First, disconnect the spark plug cable from the plug; the cable has a loop on the end that should slip off easily. Since the mower must be tilted on its side to gain access to the blade, let the mower cool if it is hot from use. If possible, drain the gasoline from the tank, or at least make sure the gas cap is screwed on tight – keep in mind that gasoline leaking over a hot engine is dangerous.

Wear gloves when lifting the mower and working with the blade. A badly bent blade is obvious, but you can check for a slight bend by measuring the distance between the blade’s end to the housing at both ends – the gaps should match. Use a stick to turn the blade about a half turn and measure again; these gaps should match the first ones.

If the cutting edges of the blade are badly nicked or dull, remove it and sharpen with a file or take it to a mower shop for sharpening and balancing. A new 22-inch mower blade can cost $20 or more so the cost of professional sharpening is often worthwhile.