Furnace Filter

Replace a dirty, flat filter with a pleated one, which has more surface area to capture dirt. It takes about 10 minutes and costs about $15.

Programmable Thermostat

Set it to get the heat going before you wake (no more shivery mornings) and to shut off when no one’s home. Buy one with the Energy Star label for about $70 and you’ll save up to $100 each year on heat. It takes about an hour to install.

Self-Adhesive Foam Weather Strip

To seal a gap in a closed door or window, apply a strip of foam tape to the top of the frame. You’ll need less than five minutes per door or window and pay $2 to $4 for 10 feet of tape. It comes in 3/8- and 3/4-inch widths.

Door Sweep and Saddle

Keep out drafts that sneak in under exterior doors by installing a door sweep (a metal strip with a rubber flap that is screwed to the bottom of the door) and a saddle (a threshold bolted to the existing one so the door meets it flush; buy metal or wood, which are more durable and weather-resistant than rubber). It takes less than 30 minutes to install both a sweep and a saddle, and they cost about $10 each.