Posted by Harold Kestenholz - Hydronic Network on March 06, 2001 at 14:32:47:
In Reply to: boiler heat damper posted by Steve Matthews on March 06, 2001 at 12:24:16:
The exact amount of heat lost up the chimney due to air passing through the heat exchangers depends upon the size (mass) of the boiler and its ability to retain heat. As it is the hot gases that heat the water in the boiler, it is the cool air that cools the water while the boiler is off. It is very difficult to make a boiler more efficient than 78% without a damper, that is why they are on the unit.
A damper can increase the efficiency significantly. The estimate can be from 6 to 20%. A boiler engineer would need to test the unit in place to give an accurate number for your local installation. If neither of these numbers bother you and you don't mind 20% of your heat to be wasted up the chimney, little else will happen by keeping it open; however, the safety circuits are disabled to eliminate the damper and the boiler is no longer under code or manufacturers warrantee.