Q. What is your opinion on furnace filters that don't need to be changed for three months? Also, how important is it to clean behind a refrigerator? It's a problem for me to move it away from the wall, but I will get a long brush to clean underneath. Is that sufficient? Is it necessary to cover my AC unit outside? Where can I find an anti-fog item for bathroom mirrors? I've tried a few places with no luck. Thanks.

A. Three months between filter changes is generally OK if the at the end of three months the filter is not chock-a-block full of dust and dander from cats, dogs, the detritus of multiple children and chain-smoking relatives. If it is, then change it more frequently. I think you are doing fine with the refrigerator. I’m more concerned that you might injure yourself wrestling with that big refrigerator out than I am about the back getting so dusty that it hampers the refrigeration compressor’s efficient operation. It happens but it’s rare.

Folks used to wrap their big window and through-wall air-conditioning units that they left in place during the winter as an anti-draft measure. Old habits being hard to break, it just seemed logical to some to wrap the stand-alone compressor/condenser units during the winter down time too. But that’s not really the case. They are designed to be outside and designed to get wet. Wrapping them can do more harm than good because the wrap can trap moisture on the unit not doing it any good. Keep ice, snow, leaves and debris off the unit and that’s all you really need to do.

I remember seeing stuff called Rain-X some time ago advertised on TV that you’d put on you car’s windshield that made rain run off so quickly that you didn’t need windshield wipers. I checked their website www.clorders.com/shellrainxsub.htm and discovered that they have a glass cleaner with anti-fog that you can order through them but you might find it at an auto-parts store locally. Back when I had enough hair to justify using a hair dryer, I just aimed the pistol-grip hair dryer at the mirror and cooked the fog off in seconds. Now I don’t even bother.

Q. Wow! My heart skipped a beat when I saw my latest BGE bill. In fact at first I thought maybe it was for two months. No such luck. Here's the bill information. We used 239 fewer kWh in January 2005 than we did in January 2004 and used 42 fewer gas therms in January 2005 than we did in January 2004. January 2005's bill $266.45 compared with $184.44 in January 2004.

I'm writing to you to ask if you can give us additional ideas on how to save energy. We live in a one-story 40-year old rambler. Here's what we've done in the past 5 years: Removed old siding shingles, added insulation and new siding; had insulation blown in the brick front of the house; replaced all windows that were metal framed with Andersen windows; added extra insulation in the attic; wrapped hot water pipes leading from hot water heater; replaced an old dishwasher with a more efficient model. Then this past year we upgraded several high-energy user items. We bought a new water heater, a water and energy efficient clothes washer, an energy efficient gas clothes dryer and had a new energy efficient heating and air conditioner system installed.

The only item remaining item on our to-do list is to replace the front door that is covered by a storm door. However, if you can think of anything else we can do, we'd be sincerely grateful.

A. You have certainly covered all the bases and your lowered usage rates reflect that-- it's just that the base cost of gas and electricity you have used has gone up and apparently wiped out the savings that you thought you were realizing by doing all that you've done. It might not make you feel any better but imagine how much bigger that bill would have been had you not done any of the upgrades with an eye to energy conservation. You should be more comfortable in the house with cleaner clothes while sleeping better, secure in the knowledge that your new water heater is less likely to go south while you slumber. The new front door won’t help that much but it will look better.