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Posted by Heatpro on January 10, 2006 at 21:01:50:
In Reply to: Over-sized boiler posted by Drew on January 10, 2006 at 19:55:46:
A gas burner that is of the power-burner type, like an oil burner can be derated, as the air thorugh it is adjusted to the fuel going in.
An atmospheric gas burner with the strips under it is designed at the factory with the right amount of flue gases passing through the fixed size of the passages above it. When you reduce the fire, ther is more air going thruough pulled upward by the heat of the walls and the fire. A small fire can 'tunnel' through the passages to touch less of the walls, so transfer less heat, reducing efficiency.
As the fire is reduced over the strip burners, the combustion of the fuel might be adversely affected; that is why the factory engineers specify a given pressure that the gas valve should be set to. Lowering the pressure at the gas valve can cause 'singing' noises as the fuel partially burns inside the burner.