A modulating burner moves fuel and air together, through a linkage or separate servos, in response to the pressure or temperature control. That keeps steam pressure or water temperature steady, extends run times and cuts cycling losses compared with on-off or high-low-off firing. Modulating condensing boilers use variable-speed fans and premix valves to do the same.
Boiler's sitting at 30 percent modulation and holding pressure, that's what it should look like on a mild day.
Also heard as
- mod
- modulating
Related terms
Turndown
The ratio of a burner's highest to lowest firing rate, such as 4 to 1 or 10 to 1.
Mod motor
The modulating motor that drives a burner's air damper and fuel valve through their range on command.
Jackshaft
The shaft and linkage system that lets one motor move a burner's fuel valve and air damper together.
Condensing boiler
A boiler designed to cool flue gas below its dew point so water vapor condenses and gives up its latent heat.