New answers tagged ducts
A reciprocating saw with a stubby metal blade works great. Make sure you clamp the workpiece down or get a friend to hold it. A long blade will bottom out on the inside and bend, so watch the blade length.
Having a take-off at the end of the plenum doesn't allow the other take-offs to maintain equal pressure - the end take-off will steal all of the airflow because it has a straight exit path. This doesn't allow the plenum to pressurize as effectively as when the direction of the airflow is impeded. You can actually visualize this by taking two styrofoam ...
IMHO: I don't believe the position makes any difference. The pressure in the main duct, for all practical purposes, is uniform. There is a slight loss at each exit duct along the main duct, but the original main duct should have been designed to handle this. However, if you added the duct to the end of an existing system, and the duct is comparatively too ...
In many jurisdictions, a plumber is allowed to remove a limited amount of asbestos pipe insulation or tape. Or put on a mask, douse the whole thing with water, and cut it off. Not rocket science here.
Dryer vents should be sealed with foil tape as they can withstand the high temperatures encountered during machine use. Other tapes, even duct tape, are susceptible to failure under the extreme heat. Non-foil tape can also catch on fire.
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