looking for a hvac answer

larry merlau

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Delton, Michigan
got a window bench that will be covering a old cold air return. the size of the old return is 4" by 30" long but the groves are only 8 slots and 2" high not sure of width.. but am quessing around 3/8" so i need to make openings in the back of the bench tolet in air to this and i have 2-2.5x14- wall registers to put in the front of the bench apron.. so how many inches of clear space do i need to make in the back? thanks for the math gerus out here for your help.
 
Is there gonna be storage in the bench? That could impede air flow.With 8 slots X 2", you have 16 lineal inches of vent space X 3/8" wide, means there's only 6 square inches of actual vent.

If there's only open space in the bottom portion, why not cut a hole the same size as the existing vent in both the front and rear of the bench, and bring the existing vent cover to the front of the bench?
 
vent on wall is in wrong position to be centered jim i have a 4" toe kick gap that i can cut out the back and open up holes threw the support legs to get air from the front. just was looking for the free air i needed. dont want to cut any more than i have to away.
 
How about raising the floor of the window seat and make the toe kick your intake? Large and no obstructions or vent covers. This assumes the seat is situated between two walls, as in a dormer, so you can fully support the front.

Larry Window Seat.jpg

Ooops.That/s for a floor vent. How about this for a wall vent? Guess it depends on how high the vent is on the wall.
Larry Window Seat 2.jpg
 
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i plan on doing something similar rennie i have it built already just looking for the amount of free air i need to get.. another words how many holes what size kind of thing i got 2 wall registers for the front apron but dont want to cut away to much of the structure.
 
I had my HVAC guy remake the duct, pulling it forward to the edge of my cabinet in the kitchen, I'll ttry to get a pic from below if it would help:)
 
no need tom thanks i just was looking for the amount of holes to make to allow for air flow. without making more than needed.. i have 2 register covers for the front already.
 
Well, each 2.5" hole will have almost 5 sq. inches of area. I'm not sure how much opening there is in the existing register, but it might be more useful to match to the new registers anyway, since that's the air you can pull. If a 2" hole fits the opening better, you get 3 square inches of area per hole. Is that the info needed?
 
fred you are on the right track, here is a picture of the old vent,, the slotted area is 27" long and 2" high.. will remove it completly and make air channel under bench to allow sufficient air..

thumbnail_20170220_064407.jpg
 
So, making some guesses....each slot is about 5" long (?), and you said they were maybe 3/8" wide. So that looks like 30 square inches of opening (unless I screwed the calculation up), and if you use the 2.5" hole you would need 6. If you have room to use a 3" hole, you get 7 sq inches per hole, and could get by (probably) with 4.
 
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