The efficiency of new boilers is given as the annual fuel utilization efficiency (AFUE), a measure of overall performance. Boilers manufactured since 1992 must have an AFUE of at least 80%. In comparison, many old boilers have AFUE ratings of only 55-65%. To get the most out of your new boiler, consider the following:

Buy ENERGY STAR (AFUE of 85% or higher)
If you want to know what manufacturers produce high-efficiency boilers, check the ENERGY STAR list. Ask your contractor about condensing boilers that are available and consider the added investment if you live in a very cold climate.

Control Options
Ask your contractor about different controls that reduce the amount of heat lost through the pipes during off-cycle periods or off-peak (warmer) days. Today there are many technologies available. Controls that modulate the boiler water temperature to reduce off-peak losses work better with condensing boilers. Ask about the cost of purchasing a boiler that has integrated controls compared to the cost of purchasing the controls as an add-on.

Low electricity usage
Tell your contractor that you would like a boiler that has low power usage. The Gas Appliance Manufacturers’ Association website includes information on AFUE and annual electricity use in its product database. The actual amount of electricity used in your home will vary with your local weather and home characteristics.

Indirect Water Heater
Modern boilers with low thermal mass and good insulation can actually make very efficient water heaters, because they don’t both heat and store water at the same time. When installing a replacement boiler, consider replacing your existing storage water heater with a well insulated indirect tank that connects to the boiler with an external loop. Even in the summer you are likely to save energy because heat losses through the water heater flue will be eliminated.