Rumble is combustion-driven oscillation: the flame's heat release couples with the acoustics of the furnace and vent and the whole system resonates. It is usually tied to air-fuel ratio, flame stability or burner head position, so techs adjust excess air, head settings or gas pressure, and sometimes change the vent or add a baffle. Severe rumble cracks refractory and shakes fittings loose.
Boiler starts to rumble right at 60 percent fire, back the gas off a hair at that point on the curve and see if it quits.
Also heard as
- combustion rumble
Related terms
Excess air
Combustion air supplied beyond the exact amount needed to burn all the fuel, expressed as a percentage.
Draft
The pressure difference that pulls or pushes combustion gases through the boiler and out the chimney.
Dial in
To fine-tune a burner with a combustion analyzer until oxygen, CO and stack temperature land where they belong.
Lazy flame
A long, soft, yellowish flame that drifts and licks the furnace walls instead of burning crisp and compact.