QUESTION: How can I determine how much of the $1,500 stimulus rebate I would receive if I replaced the windows in my home?ANSWER: Section 1121 of the stimulus package allows for a federal energy tax credit to homeowners, up to 30 percent of the cost of window and door replacement — a maximum of $1,500 for years 2009 and 2010.The tax credit is for the price of the product only and does not include the cost of installation. To qualify, windows and doors must have a 0.30 U-factor and 0.30 or better solar heat-gain coefficient.Here are a few more words of explanation, courtesy of the folks who know at the U.S. Department of Energy:The U-factor is the rate at which a window, door or skylight conducts non-solar heat flow — typically expressed in units of British Thermal Units per hour minus feet squared minus temperature in degrees Fahrenheit.For windows, skylights and glass doors, a U-factor may refer to the glass or glazing alone. But the National Fenestration Rating Council's U-factor ratings represent the entire product's performance, including frame and spacer material. Basically, the lower the U-factor, the more energy-efficient the window, door or skylight is.A solar heat-gain coefficient refers to a fraction of solar radiation admitted through a window, door or skylight — either transmitted directly and/or absorbed, and then released as heat inside.The lower the coefficient, the less solar heat the door, window or skylight transmits and the greater its shading ability. A product with a high coefficient is more effective at collecting solar heat gain during the winter. A product with a low rating is more effective at reducing cooling loads during the summer by blocking heat gained from the sun.Therefore, the solar heat-gain coefficient you need for a window, door or skylight should be determined by such factors as your climate, orientation and external shading.Confused? Go to the www.energystar.gov for a more detailed explanation.

QUESTION: We have lived in our 30-year-old home for eight years. The roof is about 25 years old. It seems to be in OK shape, but it will soon be replacement time. The house has original galvanized gutters that I have been patching. Since there are large trees near the house, we want to replace them with clog-proof gutters. What do we do?ANSWER: I'd have the roof and the gutters and downspouts replaced at the same time. If you have a roof with asphalt shingles, it typically lasts 20 to 25 years, depending on the weather. It is coming due.Clog-proof gutters are basically all the same. The difference is the installation. If a good system is badly installed, it won't work.If you are surrounded by trees, you'll need to cut them back for the sake of the roof and the gutters. For example, most readers with pine trees say the needles clog clog-proof gutters. I can attest to that. I installed guards on the gutters of the roof over the back steps to my house and have to periodically clean the sticky needles and other debris that fall from the pine tree above it.Also, I have to mention a good experience. I recently ordered the wrong blade for my Neuton battery-operated lawnmower. I called customer service. They sent me the right one, and told me to keep the one they had sent earlier because it would just cost too much to return it. Unusual.

Have questions for Alan J. Heavens? E-mail him at aheavensphillynews.com or write him at The Inquirer, Box 8263, Philadelphia, PA 19101.