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Question - I have a large glass patio door. It always seems hot near it in the summer and drafty and cold in the winter. What can I do inexpensively to block the sun and cold and reduce the drafts? - H.K.

Answer - A large glass patio door is one of the greatest energy guzzlers year-round. This is due to the mating edges that must be sealed and the large glass surface area.

In the summer, the majority of the heat is from the direct sun and from heat reflected off of the patio. Even if the door itself is shaded, direct sun on the patio radiates upward. Air leakage is not as significant a problem in the summer as in the winter.

In the winter, some of the chilly drafts are not caused by air leaks at all. Warm room air near glass get cold, even with thermal glass. This cold air is heavier than the rest of the heated room air, so it sinks to the floor and causes an apparent chilly draft from outdoors.

It is important to caulk and weatherstrip the rest of your windows and doors. Air that leaks in through your patio door must push air out from your house somewhere else.

If it didn't leak out, your house would explode. Tightening up the rest of your house also reduces your utility bills and dust in your house.

Blocking the direct force of the wind against your door reduces leaks. The amount of cold outdoor air leaking in through a small unsealed spot increases several times when a stiff wind blows against it.

Building an attractive covered wind/sun shield around your patio door helps year-round. A simple framed plywood wall on each side of your door is adequate. Cover it with a pitched shingled roof.

This also provides an excellent location to hang plants under the roof. If you rely on natural ventilation or fans for cooling, build a hinged shutter or operable window in the side that faces the prevailing summer breezes.

If you have swinging hinged patio doors instead of a sliding door, install a new door threshold seal. There are many types available - automatic, sweep, vinyl bulb, door shoe, etc. and each has its advantages.

With carpeting on the floor, install an automatic lifting threshold seal. As the door starts to open, a cam mechanism raises the seal so it does not drag on the carpeting.

Write for Utility Bills Update No. 794 showing do-it-yourself instructions for making a patio door wind/sun shield and for selecting and installing a door threshold seal. Please include $2 and a self-addressed envelope. Write to James Dulley, Deseret News, 6906 Royalgreen Dr., Cincinnati, OH 45244

Question - Is it always best to remove the old shingles before installing new ones? Does this affect the amount of the sun's heat that is transferred down through the hot roof? - T.D.

Answer - Removing the old shingles first is the preferred method, especially if they are badly cupped and curled. Reroofing over them may look good at first. After the sun heats them over the summer, irregularities from the old shingles underneath may appear.

From an energy efficiency standpoint, the extra layer of shingles will not have a great effect. Shingle color and material are most important. Light colored shingles reflect more of the sun's heat than dark ones. Metal roofs, especially aluminum, also reflect heat.