Rectification|flame ________________ is a process in which exposure of a sensing rod to flame produces a tiny current that can be sensed and used to control the gas valve. 
Modulating|a kind of gas valve that precisely controls burner capacity by adjusting the flow of gas to burners in small increments.
Net stack|a kind of temperature value needed to perform a combustion efficiency analysis, calculated by subtracting room temperature from the temperature measured in a furnace's vent or vent connector.
Reverberator|a wire screen used to cover the ceramic grids in a gas-fired heater that operates by submerged flame.
Submerged flame|a method of gas-fired heater operation that uses burning gas within two-layer porous ceramic grids.

Flame rectification 
Modulating valve
Net stack
Reverberator
Submerged flame