Energy Efficient Gas furnaces

Furnaces and boilers are the two primary means of heating most homes.  Furnaces heat the air and distribute it through the home via air ducts and vents.  Boilers heat hot water or steam and distribute it through the home in pipes and radiators.  In looking at energy efficiency of both systems the metric that is used is called the Annualized Fuel Utilization Efficiency (AFUE) number. 

Furnaces are evaluated as part of the Federal Energy Star program.  In order to qualify an Energy Star gas furnace must have annual fuel utilization efficiency (AFUE) ratings of 83% and 90%, or higher, making them up to 15% more efficient than standard models. In some cases the Energy Star compliant furnace may be more expensive than some other models but they are likely to more cost effective in the long run. 

When selecting a new furnace or replacing your old furnace it is important to be sure you get one which has the right capacity for your home.  Don't just assume that the furnace capacity you currently have is correct.  Historically many homes have been equipped with oversized furnaces because at the time heating fuel such as natural gas, heating oil or electricity were incredibly cheap.  That is no longer the case so you should always have a professional contractor do an analysis to determine your actual requirements.

Sizing your furnace is not just a function of the square footage in your home.  The contractor will also need to take into account your climate, the amount of insulation in your home and the type of materials it was built with.  Most experienced contractors now use fairly sophisticated computer programs which can calculate your design load quite accurately.  The most common analysis software is based upon the Manual J, Residential Load Calculation Procedure published by the Air Conditioning Contractors of America (ACCA).

Once the contractor has determined the appropriate load for your gas furnace they will determine the appropriate size for  ducts, supply registers, and return grilles.  In doing this they usually follow guidelines set down in the ACCA's Manual D.  The contractor should also check to make sure that you have appropriate insulation and vents to ensure that the heat your putting in is properly distributed and unlikely to leak.  If duct leaks or other air leaks are detected these should be addressed before your unit is installed.

Sometimes finding a heating and air conditioning contractor who really understands energy considerations is difficult. A great resource to go to in that case is the Air Conditioning Contractors of America (ACCA) web site at ww.acca.org.  On their site you can find a Contractor Locator which includes a special designation to identify contractors who sell and are knowledgeable about ENERGY STAR heating equipment.

Energy Star Rating for Gas Furnaces