Energy Efficient Boilers

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) rating. Gas and fuel oil boilers are evaluated as part of the Federal Energy Star program. The Energy Star program does not yet rate electric boilers. In order to qualify for an Energy Star rating a boiler must have an annual fuel utilization efficiency (AFUE) rating of 85% or greater. 

A number of changes have been made in oil and natural gas boilers in recent years to make them more efficient.  First, many use electric ignition instead of a pilot light which means energy is not wasted keeping the pilot light going. Second, they also use new combustion technologies that extract more heat from the same amount of fuel.  Finally, many use a sealed combustion chamber that uses outside air to fuel the burner, reducing draft and improving safety. Because of these additional features 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. 

In selecting a boiler one of the first decisions you must make is what type of fuel you are going to use.  This is a critical decision because of the recent dramatic rise in fuel costs, particularly fuel oil.  The cost of fuel oil increased by about 49% during the 2007-2008 heating season.  The cost of natural gas also rose during this same time frame but by far less, rising about 16.2% according to the U.S. Energy Information Administration.  As a result natural gas is, in 2008, a far cheaper approach for heating water than fuel oil.  If you currently have a fuel oil boiler you might want to get an estimate from your local heating/cooling contractor about switching to either a natural gas boiler (assuming natural gas is available in your area.)  If you do not have access to natural gas in your area one other option is an electric boiler.  A few years ago electric boilers would not have even been considered an option because they were so much more expensive than natural gas or fuel oil.  However, the Energy Bible recently completed an updated comparative analysis on the cost of electric boilers versus fuel oil boilers given the recent changes in fuel prices and electric boilers came out as less costly than all but the most efficient (AFUE 95%) fuel oil boilers.  A lot depends on electric costs in your area but electric boilers, though not cheap, could end up being a better alternative. 

Another factor to consider when getting a boiler is its capacity.  If you are replacing an old boiler don't just assume that the boiler capacity you currently have is correct.  Historically many homes have been equipped with oversized boilers because at the time heating fuel such as natural gas, heating oil or electricity were incredibly cheap.  That is no longer the case.  You want to avoid getting too big a boiler because not only will it waste heat, the boiler will cycle on and off more frequently than necessary which wears out its components.  Always have a professional contractor do an analysis to determine your actual requirements.

Sizing your boiler 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 capacity for your boiler they will determine the appropriate placement and dimensions of pipes and radiators.  If you are replacing your current boiler the contractor should examine the pipes and radiators in order to determine if any adjustments are needed given the capabilities of the new boiler. They should also check for any signs of leaks or rust in your existing pipes or radiators. All leaks 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. 

Listed below is a table showing the Energy Star Ratings for boilers.  It includes the AFUE rating for each model.  The higher the rating the more efficient the boiler is.

Energy Star Boiler Ratings

(last updated February 1, 2008)