Winter is approaching, and despite predictions that the months of December to March will feature milder weather and lower energy prices, it never hurts to be prepared for the worst.

If we don't cover everything on the to-do list today, we still have a few weeks to cut away the weeds to get to the shrub, so to speak.

Consider your furnace. You might want to exchange your furnace for a newer model. Every year, according to federal statistics, 2.5 million American homeowners do. Yet of the 43 million residential oil and gas furnaces in operation in U.S. homes, the statistics say, one in four is over 20 years old. Many new furnaces on the market are 25 percent to 40 percent more efficient than older models. The Environmental Protection Agency's Energy Star program promotes furnaces using a "condensing technology" as the most efficient. The efficiency rating on the label of every new furnace tells how much of the total energy the furnace uses will be delivered to the home as heat. The higher the rating, the better.

Stop the heat loss. Why buy a new and more efficient furnace if the heat escapes? Leaky windows and doors can be big sources of heat loss, so don't skimp on the weather-stripping around them. (If you have particularly leaky windows, you may want to use a plastic cover that shrinks onto the windows - it's less unsightly and damaging than stapling plastic to the frame.)

To decide where to install weather-stripping, try the candle test. Light a candle and move it around the window or door on a windy day. Note where the candle flickers; that's where the weather-stripping goes.

Make sure your windows have no cracked or broken panes. To extract a broken pane, remove the putty and glazing points, then have a piece of glass cut to fit, replace the points, and reglaze.

Also check the rubber seals around the glass of storm doors and windows. If they must be replaced, install weather-stripping rated for exterior use on doors and windows.

This may be the time to consider replacing your old, leaky windows with new energy-efficient ones, since there is an energy tax credit available for qualified ones (the windows themselves, not the installation costs).

Even with the credit, however, new windows may be out of reach for those on fixed incomes - those most vulnerable to energy-price spikes and who tend to live in older houses. Experts recommend replacing leaky windows gradually, starting with the most uncomfortable room.

Most windows are double-hung. The upper sash is rarely opened, so you can caulk it shut. The lower sash can be sealed with weather-stripping for $1 to $2 a window. Tighten them up, use rope caulk, make sure they lock. The same goes for exterior doors.

Seal before you insulate. As all that warm air flows out of a house, cold air is pulled in to replace it, since the air pressure inside must equal the outdoor pressure. The temptation, of course, is to turn up the thermostat, but heat will still head for the door, and you'll still be cold.

What about insulation? Great idea, but experts say that before you insulate, you need to use foams and sealants to close any penetration to the outside, such as at the ends of joists at the front and back of the house.

Sealing - tuck white or black plastic bags into the cracks (clear ones decompose) - prevents heat from escaping and moisture from entering the attic, without interfering with the required ventilation. Then you can go ahead and insulate. Some experts prefer cellulose insulation rather than fiberglass batts in attics. Cellulose is ground-up, recycled newspaper treated to make it fireproof, and it fills smaller spaces more easily than fiberglass.

The basement is another place where air sealing will reduce heat loss and moisture intrusion by reducing incoming air flow. Basement windows tend to be the worst cared-for, so make sure too much air isn't escaping through them.

We've barely scratched the surface. Next week's Your Place will provide more hints as we answer questions.

Want Alan J. Heavens' advice on a home-improvement project or purchase? E-mail him at aheavens@phillynews.com or write to him at The Inquirer, Box 8263, Philadelphia 19101.