Furnace Terminology

As Furnaces become more energy efficient, it seems that the language one must speak to understand them also becomes more complex. Thankfully, many sites have taken the opportunity to provide alternate definitions in hopes of explaining these terms. We also have a glossary at Sinclairair.com. However, there are several types of furnaces. The website at http://www.atcoenergysense.com/Tools+and+Resources/Articles+and+Fact+Sheets/Residential/FurnaceTerminologyandTechnology.htm provides a couple of helpful definitions.

"Burner Controls
Today’s heating systems are manufactured with single-stage, two-stage or modulating burner controls.
Single-Stage: These burners operate with very little flexibility. Basically, the burner is fully on (operating at full fire) or fully off. Older conventional furnaces in many homes still operate in this manner.
Two-Stage: Much like having two furnaces in one. During mild winter weather when the demand for heat in the home is low, the burner operates at low stage. During colder temperatures, when the heat loss in the home is at its greatest, the burner adjusts to its higher stage (full capacity). This system cycles the furnace on and off more effectively, offering increased energy savings compared to a single-stage furnace.
Modulating: These burners have the most flexibility in adjusting to heating requirements (moving up and down continuously in relation to the home's heating demand). This system offers greater efficiency and comfort compared to single- and two-stage gas valve systems."