You’ll save energy and money by having your furnace tuned up periodically. Gas and propane furnaces can go 3 to 5 years between tune ups and longer if you perform filter maintenance regularly. Oil furnaces need service once a year because they get dirty and need annual cleaning and adjustment.
Changing filters is one of the key maintenance tasks to keep your furnace running efficiently. Without a filter, your blower, furnace, and air conditioning coil can get dirty and these items are all difficult and expensive to clean. Make sure that you know where your furnace filter is located and what size it is. Inspect it periodically, and replace it when it is dirty. If you have a washable filter, clean it with soap and hot water.
If you have a combustion furnace–one that burns gas or oil–select a contractor who uses an electronic combustion tester. Electronic analyzers can guide the technician to adjust the furnace for optimal performance and safety.
Duct air leakage is one of the most severe energy-wasters in your heating system, and this applies to both electric and combustion furnaces. The best heating contractors will check your ducts for air leakage, and seal the worst leaks. They should start by sealing all the larger joints near the furnace, and then work out towards the branch ducts. Strangely enough, duct tape isn’t a good choice for sealing ducts because its adhesive usually fails after a short time. Duct mastic, available in cans or buckets, is an effective and permanent material for sealing duct air leaks.
Here is a filter mounted in a return-air register known as a filter grill.
See The Homeowners Handbook to Energy Efficiency or Residential Energy: Cost Savings and Comfort for Existing BuildingsChapter 6 for more information. For professional information about heating systems and energy efficiency see Saturn Hydronic Systems Field Guide.