Every fall I get an email from a company offering to audit my home for four hundred dollars. I have never paid for one, and my heating bill is lower than my neighbors with the same house.

The work that matters takes an afternoon and costs less than a nice dinner.

Find the air leaks first

Do not start buying anything. On a cold windy day, hold a lit incense stick or a damp hand near the edges of your doors and windows. Move slowly. Where the smoke wavers or your hand feels cool, you have found a leak.

I found seven. Two were obvious at the front door, and five were places I never would have guessed: the gap under the kitchen sink cabinet, the dryer vent flap, the outdoor faucet, and both electrical outlets on the north wall.

The list, cheapest first

1. Door sweep and weatherstripping, about fifteen dollars. The gap under an exterior door is usually the biggest single leak in a house. A screw on sweep takes ten minutes.
2. Foam outlet gaskets, about five dollars for a pack. Outlets on exterior walls leak quietly and constantly. Unscrew the cover, put the gasket behind it, screw it back.
3. Caulk around windows and pipes, about eight dollars a tube. Look for cracked or missing caulk on the outside of the house around window frames and where pipes enter. Clear silicone and a caulk gun.
4. Plastic window film for the worst window, about ten dollars. It looks ugly and it works. Use it on the one or two windows you never open.
5. Insulate the outdoor faucet, about five dollars. A foam cover keeps the pipe from freezing and splitting.

Do not caulk over a window you open. It sounds obvious. I did it anyway on a kitchen window and spent twenty minutes with a putty knife undoing my own work.

Two free things that matter as much as the caulk

• Open curtains on south facing windows during the day and close them at dusk. Free solar heat in, free insulation after dark.
• Set the ceiling fan to reverse. Most fans have a small switch on the housing. Running clockwise on low pushes warm air down off the ceiling, and it makes a room feel several degrees warmer.

The other thing nobody mentions: turn your water heater down to 120 degrees. It is a two minute job with a screwdriver, it is completely safe for a household without a dishwasher sanitizing cycle, and it saves real money every month.

All in, I spent about forty two dollars and an afternoon. The furnace runs noticeably less, and the front room stopped having that cold draft along the floor.