Cold air return sizing


Old 03-17-17, 12:47 PM
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Cold air return sizing

Hi all, I have a question regarding a cold air return that I have to move. We had a return taking up two joist bays in a wall that was removed (see photo below). I am moving the return to the floor right in front of the wall with the thermostat (see photo). My questions is how big does the opening need to be? I was thinking a 7"x14.5" since this was the size of the two joist bays.

What are your thoughts?

Thank in advance!
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Old 03-17-17, 01:30 PM
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Against code for returns to be in the kitchen. But no way would I make them smaller.
Old 03-18-17, 07:53 AM
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The return is going in the living room, not the kitchen. I am just trying to figure out what size it needs to be, since its going from a wall return that took up two joist spaces, to a floor return.
Old 03-18-17, 01:56 PM
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Hi rodin,
Not a hvac pro but typically a home has too little return flow from the start. The supply side provides warm air due to the force of the fan. The return side sends the air back to the furnace due to the pressure inside the house. Too little return capacity and that pressure increases which also forces more air out through the shell of the house. Too little can also cause the furnace to get too hot and trigger a high limit safety. Bouncing off of the high limit isn't good.

If you do reduce the return where you are working look to increase it elsewhere or best go through the determination process to see how much is correct.

Old 03-31-17, 04:14 AM
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cold air returns

In most cases you should have at least as many cold air return grills as supply registers. One more or one less will not make much difference as long as you have enough of each to satisfy the needs of the HVAC system. Other things to consider; do you have air conditioning in your residence? If you do, you should have high and low return/registers. ( highs open summer and lows open for winter). I noticed you are moving it to in front of the adjacent wall. Can you put it in the and not on the floor? Can you put in a double register/grill and not a single. Most homes today do not have enough supply registers or return grills and the duct work is too small, so you have a noisy system.
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