Cape backdraft damper vs butterfly damper
After reading some positive reviews on GBA, we recently purchased a 4″ Tamarack cape backdraft damper (https://www.tamtech.com/product/cape-backdraft-damper/) to replace a bathroom exhaust fan damper that flapped on windy days. We thought it would produce a superior seal, but after seeing it up close, we fail to see how it can effectively seal a backdraft. There’s no retaining mesh or wire to hold the cape crosswise to the flowpath when in a backdraft condtion, so how does it seal?
Even if there was such a retainer across the flowpath, how effectively does the cape actually seal? The data table on page 2 of Tamarack’s own spec sheet for this product (https://www.tamtech.com/wp-content/uploads/2021/06/CBD-SPEC-1.pdf) indicates the damper is superior only at the highest backdraft condition. At all other backdraft pressures, a butterfly valve is superior.
Am I missing something? Is it intended to be used in series with a screen, another damper, and/or some other duct component I’m overlooking?
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User ...642,
I don't know how effective the Tamarak is. The ones that close the tightest are variations on this design. A few manufacturers make them. They aren't pretty though.
https://www.amazon.ca/dp/B0BCP9W7V1/ref=sspa_dk_detail_1?
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Thanks for making that post, I'd never heard of those. From the look of the youtube video at the link below, there's no screen involved. The fabric just collapses by gravity once the exhaust stops - and presumably wind coming in from the outside just flattens it further against itself. The installation would have to be horizontal I guess. And I suppose lifespan will be affected by what the fabric is made of and how its attached. Also, I don't really grasp their test readings. Surely there is something more to that? Here's the testing video I found:
https://www.youtube.com/watch?v=X1xja1iZPyU&t=89s
The advantages of the Tamarack Cape Air Damper are that it should be quiet and open with very little pressure. You should already have either a butterfly or flap damper at the fan. The Cape Air Damper doesn't create a perfect seal but should substantially slow cold outdoor air from getting into the duct.
If you consistently have enough wind to make your wall cap damper flap, it may or may not solve that problem. If you use it to replace the wall cap damper, I would expect it to reduce the chance of the damper at the fan making noise, but every situation is different.
I installed a Cape Air Damper in my home, and I'm not thrilled with it. The fabric is too rigid to collapse fully under its own weight, and it allows about the same amount of cold air to "seep" through the damper on the range hood as an open duct would. I suppose it might collapse more fully if there were a strong wind pushing on it, but I haven't been able to observe it under those conditions.