Im where houses are 200 yrs old, but AC is the only reason you actualy
need returns on every floor, sure its probably more even heat with
returns but I think his are undersized, even a small 2" vent in the
basement would help and circulate heat better, but if he has AC he
need a pro to evaluate his ductwork sizing, whith my new unit thats
exactly what the installer did and found my returns to small, we added
alot more and it help balance temps.
Parts of our house are over 200 years old in fact... and the central
heating was probably put in about 100 years ago.
We do plan to put in AC which as you note requires returns on the higher
floors to work properly -- in fact, one of our reasons for not investing
in the HVAC work now is that we want to do it all right when we add AC
and do renovations rather than doing it half-assed multiple times...
Actually, I think the banging problem became much worse because I
recently closed up an "inadvertent" basement return. Specifically, the
bottom end of the plenum was open but sitting on the rough basement
floor. I had previously used metal tape to try to seal it off but
recently did it right with a sheet metal cap. So, in a sense you are
But my understanding is that it is not a good idea to do that for
1. It draws in the cooler (unheated) basement air which needs to be
heated and ultimately results in either heating the basement or
drawing in more cold air from outside since the air has to be
replaced from somewhere.
2. The negative pressure could draw in more radon (and we have that here
in granite-laden New England). This is a concern particularly since
our basement floor is 150 years old so it is not fully intact and we
also have a crawl space with only a loose fitting vapor barrier
covering the raw earth.
3. If there are any open combustion chambers in furnaces or water
heaters, the negative pressure may draw combustion gasses and CO
into the basement and from there through the return into the house.
3. More generally, you will draw in fumes and other potentially
undesirable odors, gasses, etc. from the basement.
You don't necessarily need to stiffen the duct. If you can get inside
you can wedge a piece of wood between middle of the sides that 'oil can'
(pushing them apart).
You can put blocks of wood on the center of the sides that 'oil can' and
tie a rope around the duct to push the blocks in. (With a little thought
you could the same thing much better.)
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