What is a condensing boiler and why are they so efficient?

This winter, wouldn’t it be nice to get all the warmth and comfort you want at home, but use less natural gas, oil, or propane – and save money on your utility bills – while doing so? With a condensing boiler you can.

All boilers produce hot water or steam that is distributed throughout your home via radiators, baseboards, or an in-floor radiant system. In this process, boilers produce water vapor containing heat during combustion.

A conventional boiler will exhaust the water vapor and the heat is wasted. A condensing boiler, on the other hand, recovers the heat from the water vapor and puts it back into the boiler. This allows a condensing boiler to use less fuel to produce the same amount of heat. Same comfort, less fuel, lower bills.

Consider the Annual Fuel Utilization Efficiency (AFUE) rating of a boiler, which is a measure of its efficiency. A conventional boiler typically has an AFUE of 70-80%, with more efficient versions reaching 85% AFUE. Condensing boilers typically have an AFUE of 90-95%, with some manufacturers even claiming 98% AFUE on certain models. These ratings are readily available when comparing models and are a good shortcut when you’re shopping for a new boiler and have efficiency in mind.

However, in order to get that level of efficiency out of your condensing boiler, make sure the boiler’s outdoor reset controls are installed. These signal the boiler to run slightly cooler in mild temperatures, allowing the water vapor to condense.

Do you want another reason to consider a condensing boiler when it’s time to upgrade your heating system? How about 1,600 reasons?

Mass Save offers rebates up to $2,400 on the combination of a condensing boiler and on-demand hot water heater (also known as a tankless water heater). Check out our gas heating rebate page for details.