GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted Hamburger/Search Icon
Green Basics


A New Generation of Boilers Is Super Efficient

Heat and hot water, too

Hot-water boilers can burn a variety of fuels, including #2 fuel oil, natural gas, propane, and biomass such as wood or compressed wood pellets. But they aren’t popular in the United States: hot-water heating systems accounted for about 2% of all heating systems installed in new houses in 2007, according to the U.S. Census Bureau.

Unlike hot-air furnaces, boilers can’t be used for air conditioning or humidification, and boilers are typically more expensive. But hot-water distribution systems are clean and usually quiet, and boilers can pull double duty as a source of both space heat and domestic hot water. Hydronic distribution systems are usually more efficient than forced-air duct systems, many of which are plagued by leaks. Sophisticated controls like outdoor resets can help to minimize boiler fuel use.

Government efficiency minimums. Federal regs require that boilers burning fossil fuels have a minimum annual fuel utilization efficiency (AFUE) of 80%. That means 80% of the fuel consumed must go directly to heat and no more than 20% is wasted.

But boilers with much higher efficiencies are on the market, including condensing boilers fired by natural gas with efficiencies of more than 95%. In cold climates, high-efficiency boilers offer significant fuel savings that should justify their higher initial cost.

Newer gas boilers are highly efficient

The best are direct-vent modulating-condensing boilers, which increase efficiency by extracting additional heat from the condensation of flue gases. Rather than relying on a simple on-off switch for the burner, these boilers modulate the gas flame depending on demand, another fuel-conserving feature. Sealed combustion direct-vent units draw combustion air from the outside the house, cutting the risk of back-drafting, and they can be vented through plastic pipe, eliminating the need for an expensive masonry chimney. Many are small enough to be hung on a wall.…

GBA Prime

This article is only available to GBA Prime Members

Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and construction details.

Start Free Trial

One Comment

  1. Alan | | #1

    Biomass: new life for oil-fired boilers
    Fortunately, there are greener options for people who already have an oil fired boiler installed. I really like Pellergy's conversion system and have seen several homes operating on wood pellets, a locally sourced and renewable biomass. There are thousands of these systems that have been in use for over 20 years in Norther Europe and now they are being made right here in the USA! Check out their websites...

Log in or become a member to post a comment.


  • Green Basics

    Balanced Ventilation

    UPDATED on March 13, 2015Balanced Ventilation Is Appropriate for All Climates

  • Green Basics


    The Highest Efficiency Rating Is Found in Condensing Furnaces

  • Green Basics

    Space Heaters

    A Space Heater Can Be the Sole Source of Heat in a Small, Well-Insulated House

  • Green Basics

    Hydronic Systems

    UPDATED on April 18, 2014Hydronic Systems Circulate Hot Water


Recent Questions and Replies

  • |
  • |
  • |
  • |