HTP - May 11, 2016

Your Guide to Understanding Heating Terms

If you're new to the industry, or if you're a homeowner trying to figure out your best heating option, you may be coming across some terms on our site (and others) that you don't fully understand. These may be words or phrases such as "the unit's turndown ratio," "BTU output," or "drainback system." We at HTP want you to have the best experience while navigating through our site and deciding between our various products. We have come up with a glossary of heating terms to help you through your search process.

Take a look at some of the terms below. To view the full glossary, click here.


AFUE (Annual Fuel Utilization Efficiency):
an efficiency rating expressed as a percentage, based on a federal government test procedure. The test includes combustion efficiency, flue loss, and flue loss in the burner off cycle. The data is calculated to simulate a complete heating season of operation. AFUE measurements are calculated for residential boilers only.

Air handler:
a generic name for a device consisting of a blower and a finned-tube coil. It is used to either heat or cool the air passing through it based on the temperature of the fluid circulating through the tubes of the coil.

a term often used to describe gas burners that are designed to operate directly exposed to (unpressurized) room air.

BTU (British Thermal Unit):
the amount of energy required to raise one pound of water by one degree Fahrenheit.

Buffer tank:
an insulated, water-filled storage tank that forms a link between a heat source and its related hydronic distribution system. A buffer tank is often used to reduce the inefficiencies of short-cycling when low-mass boilers need to operate under low load conditions.

a term used to describe a boiler control feature that allows multiple boilers to be linked and sequenced to function together. Cascading systems allow for increased turndown ratios and built-in redundancy in case of boiler failure.

Closed-loop system:
a piping system that is sealed at all points from the atmosphere.

Written by HTP