Provided by the Cold Climate Housing Research Center (CCHRC)
Boilers today offer a wide range of customized options to maximize efficiency. Alaska’s many heating days justify paying for the most efficient system possible up front, since the extra money will be paid back several times during the system’s operating lifetime. But because of the many variables involved in selecting a boiler for your home, there is no perfect system that works for everyone. Ensure that whomever you hire to provide, install, or retrofit a system is aware of the fine details and performs the necessary calculations. These calculations are especially important given the sophisticated components and sensors required by today’s most efficient boilers.
First, the basics. Boilers heat water, which is pumped through a system of pipes and radiators that conduct heat into your rooms. Boiler efficiency is measured by annual fuel utilization efficiency (AFUE). There is some debate over AFUE ratings because they do not account well for heat loss from boilers that maintain operating temperatures throughout the day. Also, AFUE does not measure heat loss from boilers or pipes that are located outside of insulated living spaces such as attics, basements, and garages. AFUE will not account for room heat that escapes out open flues. Nevertheless, AFUE remains a basic standard.
Most boilers are connected to a baseboard loop system, which is really just a series of low-profile radiators that distribute heat along the length of a pipe in a room before returning water to the boiler. A single thermostat triggers heating cycles. New boilers are required to attain a minimum AFUE rating of 80 percent, which means 80 percent of the heat generated is useful heat instead of energy that escapes up the chimney.
An alternative to baseboard heating is to install a radiant floor system. In this scenario, loops of pipes are placed into your subfloor to heat from the floor level up. This arrangement can produce more even heat throughout a room than baseboards because the whole floor space can be crisscrossed with pipes. Also, a radiant floor system has the benefit of producing more thermal comfort–fewer arguments over whether the room is too hot or cold–because more of the heat is felt in the living space instead of rising to the ceiling.
The next major decision is whether to install a standard combustion boiler or a condensing boiler. Condensing boilers generate more useful heat by extracting energy from flue gas and condensing the water vapor created by the combustion process. This process can achieve AFUE ratings of 90 percent or greater. Since condensing boilers must operate at lower temperatures for maximum efficiency, they perform best with heat emitters such as radiant floors that also utilize lower temperatures.
Another boiler option is a low mass boiler that purges system heat at the end of each operating cycle to minimize off-cycle jacket losses to the boiler room, and convective losses up the flue. Sealed combustion systems can work with different types of boilers and may offer further fuel savings; they require an exterior air source and a dedicated vent.
A boiler fitted with an outdoor reset, which senses outdoor temperatures, can increase efficiency by reducing the boiler system’s water temperature as low as possible.
Take a look at the Department of Energy’s website on the subject at: https://www.energy.gov/energysaver/heat-and-cool
The Cold Climate Housing Research Center is an industry-based nonprofit based in Fairbanks, Alaska that develops and tests energy efficient building technologies for the north. The articles and videos included in this guide are part of its mission to promote healthy, sustainable, affordable housing in Alaska and beyond. Find more at cchrc.org.