Boilers and AFUE

							Boilers and AFUE
AFUE or, if you prefer, annual fuel utilization efficiency is how the HVAC industry measures the
heating efficiency of water heaters, hydronic boilers and gas furnaces. AFUE is a particularly
good way to estimate the efficacy of a given system, since AFUE is not a purely mechanical
performance metric, but an estimate of operational efficiency during realistic operating
conditions. In other words, AFUE represents how efficient a given system will be when it is
running in your home instead of the laboratory.


Modern hydronic boiler systems usually average over 80% AFUE. You should invest in a boiler
than runs less than 80% AFUE only if you have a very good reason. Higher is always better.
The higher the AFUE, the less you spend every year on energy.


Boiler fuel can have a significant effect upon overall efficiency and, therefore, AFUE
performance. Heating oil, natural gas and propane produce similar operational effects, typically
greater than 80%. Firewood produces the lowest AFUE rating due to lower combustion limits.
That doesn’t necessarily mean a firewood powered system is more expensive. If you chop your
own wood, then fuel cost may not be a major issue for you.


Boiler Control Systems
Like any other modern convenience, the latest generation of boiler systems are equipped with
sophisticated computer controls. Most systems intended for domestic operation are going to be
compatible with a programmable thermostat, but it’s always something you should confirm
before you buy just to make sure. A programmable thermostat is a great way to control any
HVAC system and a feature every home should have.


Thermostats aside, different boiler systems use slightly different controls, but there are many
similarities between systems. Most make use of modulating operation to increase overall
efficiency. Basically, modulating operation uses a microprocessor to monitor system needs and
adjust boiler operation rate accordingly. In other words, your boiler isn’t wasting energy when it
doesn’t need to. Software like this helps new systems save energy even without mechanical
technological advancement. Modulating operation is something you want if you’re going to
spend money on a new condensing or hydronic boiler.