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Attic vent fan can be a valuable addition

(ran HP HN HS editions)

Question: My attic gets above 150 degrees in the sun and I plan to install a temperature-controlled attic vent fan to lower my air-conditioning costs. What type of vent fan is best and how large a vent fan should I get? G. R.

Answer: Installing an automatic attic vent fan can lower the air-conditioning load. By cooling the attic temperature as much as 50 degrees, you should also feel much more comfortable inside your house, especially in second floor bedrooms. High attic temperatures can also deteriorate the lumber.

There are several attic vent fan choices available. A solar-powered electric attic vent fan is the most efficient, easiest to install, and runs for free. Since it is powered by the sun, the brighter and hotter the sun is, the faster the fan runs. This makes it a perfect fit for attic cooling.

Some designs have the small solar cell panel (converts sunlight directly into electricity) built into the top of the vent fan. Others use a very small (less than one-foot square) solar cell panel on the roof next to the fan. You can use metal angles to face the small panel more directly toward the sun for more electricity output and better cooling.

You just remove a few shingles and saw a 12-inch hole in the roof. Nail the 12-volt fan in place and seal around it. Replace the shingles. Run the wire from the solar cell panel to the fan and it starts. You can also get solar-powered vent fans designed to mount vertically in the gables.

An automatic temperature-controlled 120-volt electric attic vent fan is also very effective for cooling your attic. These can provide up to 1,600 cfm (cubic-feet-per-minute) of air flow to cool even large attics.

An adjustable thermostat is used to control the temperature at which the attic vent fan automatically switches on. The thermostat keeps it from running too much and wasting electricity.

In the winter, you can install a humidistat to control the fan. This eliminates potential moisture problems during extremely cold spells. With adequate attic floor insulation, it will not increase your heating bills.

A rule of thumb for sizing an attic vent fan is that you should have a minimum of 10 complete air changes per hour. With a typical pitched roof, a 900-square-foot attic would require a vent fan capacity of 630 cubic feet per minute (cfm) A 1,500-square-foot attic would require 1,050 cfm vent fan. The best location for the inlet air vents is under the soffits.

You can write to me for Utility Bills Update No. 023 listing addresses and telephones number of manufacturers of solar-powered and electric-powered attic vent fans, air flow capacities in cfm, product information and a chart showing recommended sizes for vent fans for various attic sizes. Please include $1.50 and a self-addressed business-size envelope. Address below.

Window film

removal tips

Question: I have old permanent-type of window film on my windows and I want to remove it and install the self-cling film you wrote about. What is the easiest way to remove the old window film? _ J. L.

Answer: There are two methods. First, using a single edge razor blade or window scraper, scrape the film loose from the top edge. Spray the exposed area with a solution of half ammonia and half water. Slowly work diagonally across, peeling it from top to bottom.

It this doesn't work well, spray the film with the ammonia solution. Cover the window with plastic and let it stay wet for 10 to 12 hours.

Repairing glass

block windows

Question: I have energy-efficient glass block windows for security and several are cracking at the corners. How can I stop the cracking? G.B.

Answer: The blocks may crack from moisture getting into the mortar joints. If it freezes and expands, it can crack the glass. Different expansion rates between the glass and the wood or metal frame can also cause cracks.

You should carefully remove the old mortar and remove the blocks. When resetting the blocks in the frame, set them in an expansion joint or soft caulk. Make sure there are no voids in the mortar where moisture may collect between the blocks.

James Dulley is an engineer whose column on cutting utility bills appears twice a month. Questions can be addressed to James Dulley, Cut Your Utility Bills, the Times, 6906 Royalgreen Drive, Cincinnati, OH 45244.