Can A/C input and return vents / duct work be on the same wall and still work?
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We are trying to decide and having difficulty finding answers from the local HVAC. Ex: they seem stuck on putting ERV’s in same duct work as a/c as well as placing the duct work in unconditioned space.
We are trying to see what is best for our build / budget.
Specs of home:
40’ x 72’ slab on grade with in floor heating and direct vent gas fireplace for shoulder months
Climate zone 5a
Using attic trusses with knee wall to condition attic 12’ wide by 72’ long down the center of house to keep duct inside envelope
Installing Zehnder and ducts in attic
Room sizes: 36’ x 21’ x 9’ living room / kitchen
3 Bedrooms: 12 to 15’ x 13 to 15’
Focusing on Zip R6, mineral wool etc for insulation
A/C only needed 2 months a year in which we try to keep within 10 degrees or less of outside temp.
Every room will have at least 12 inches or more of conditioned attic space above it.
Questions:
What is the best (and cost effective) way to a/c the house, keep the duct work inside conditioned space and for it to work together with the Zehender?
We have entertained mini splits, but don’t want to look at them on the wall. The ceiling cassettes are higher cost as well as harder to service / clean. We have also thought of drop the ceiling to create a chase for the duct work and we are not crazy about that too.
HVAC contractors want to bury ducts in insulation in unconditioned part of the attic in which we said no. They argue the return duct has to be opposite side of the input air duct to create circulation across the room. Can you put the a/c air output duct up high on the wall and on same wall put the return a/c duct lower to the ground (and possible opposite corners of wall)? Would that create enough circulation especially if we have the Zehender vent running in the middle of the same wall too?
We are not sure what we are doing for a dehumidifier as we think we may need that too.
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Replies
They're right -- ideally you want the supply and return ducts on opposite ends of the room, going in the long direction if the room is anything other than a square. This helps to ensure maximum crossflow through the room, which helps to keep temperatures more even. Putting the supply and return vents on the same wall in anything but a very small room is going to "short circuit" the airflow, leading to large thermal differentials across the room -- which will make for an uncomfortable room!
Do you have any other way to route that duct work to keep it out of the attic while still putting the vents on opposite ends of the room? You could potentially build a soffit along the ceiling, although that would visually intrude onto the interior of the living space.
Bill