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danged Vent Dampers
If you are talking about Ameri-Therms, they were sued and these unit pulled off the market. They have four valve leaflets, much like a heart valve except they are bimetal. As the unit fires, the heat causes the leaflets to open (hopefully) allowing some flue gases to pass. Some don't. Take a look at these pics of a 3" and 4". Note how the leaflets still posed considerable turbulence to the flue even when opened (here, I'm using my pen). Sometimes the leaflets would hang up and fail to open. Others, the rivet would fall out (as seen here) and snag.
The IFGC 503.14 simply requires all vent dampers be listed. They do not exclude bimetal or mechanical types. It also does not specifically name ANSI Z21.68 as the listing which applies nor does it come out and require any sort of safety interlock or spill switch. Most electric automatic vent dampers are interlocked to the gas control. On a call for heat, the damper must open first. Some actually have a microswitch to prove it is wide open. Next, the unit either fires or goes into a pre-purge then fires. Standing guard is a solitary spill switch. When the thermostat is satisfied, the burner cycles off. Some units then post-purge. Once purging is complete, the vent damper closes so as to minimize standby losses and dilution air up the stack. This boosts the unit's overall efficiency rating (AFUE).
Another peril with these dampers is they are seldom screwed in. Being made of heavy stainless steel, it is hard to drill through with Zip screws so often, they can easily fall apart.
If you need a code reference in shooting down this brand of vent damper, simply look at the label I showed you. Do you see a listing mark? That AGA mark is a design certification--not a listing mark from a recognized testing lab. Since these dampers are unlisted, they must go.
HTH.
Bob
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disgusted with some people on this forum. Out of here!
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