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air return and register size

3K views 12 replies 7 participants last post by  mikem201 
#1 ·
If I wanted to add a register and and cold air return to a room does anyone know of a good way to determine the size that should be used?
 
#2 ·
that questions is best answered with a little bit of science and a little bit of experience. The science is found with a manual j calculation for the room. man j takes into account the size if the room, the size of doors and windows, the wall and insulation type and the north, south,east, west orientation of the room. You will also need to know the size of your current system in btu's and its current static pressure. You will have to also design the placement of the supply and return in relationshiop to each other, as well as to the throw of air and the air movement within the room and the relationship of where you are trying to keep comfortable.

the experience on the other hand is all about how to "run" the duct within the limits of the homes construction, as well as the craftsmanship of the install.

so, start by checking out manual j, static pressure, your hvac equipment, where the duct could run in the wall or ceiling or crawl space, what materials you would use to run the ducts etc.... so, bottom line is that it can be done, by guess, by science or by a pro... all of which are your call...
 
#4 ·
What kind of typical room is it. Where is it, east, west, north, south exposure, ceiling height, how many windows, any doors to the outside.
 
#8 ·
6" diameter is "standard". One of each seperated by enough distance so the air doesn't come in one and get sucked right back into the other.

Put a damper in the supply run so that you can adjust the amount of air/heat being delivered.

Is this answer exact? No. Guaranteed to be the correct answer? No. Without knowing the exact heat loss of the room and the capacity of your existing system and where and how you'll be connecting to it it's a generic answer from generic information.
 
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