Adding return air


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Old 07-24-12, 06:47 PM
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Adding return air

Want to add (4) 12x12x8 ceiling return air.

Should each of these have their own return flex duct to the main return air box, or can I "y" them together and run one flex duct line back to the return air box?

If I can "y" them, does the single flex duct back need to be larger?

Thanks
 
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Old 07-24-12, 07:52 PM
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Yes after each grill the flex will have to get larger. I'd recommend each vent have it's own flex for ease of balancing
 
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Old 07-24-12, 07:59 PM
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Im a little confused by your response. Did not know return air needed to be balanced?
 
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Old 07-25-12, 07:28 AM
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Absolutely - just as important to balance the returns as the vents and the vents to the returns.

Proper HVAC work is much more complex than many people inuit.
 
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Old 07-25-12, 09:31 AM
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Thanks, I have always read that you can never have too much return, but never that it needs balancing.

No to read on how to do that!
 
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Old 07-25-12, 09:39 AM
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You can have too much return, especially if you're pulling air from an area where gas combustion is occurring (water heaters, furnaces,...).
 
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Old 07-25-12, 10:15 AM
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well yes of course, none in bathrooms, kitchen, utility room or garage.

Excluding these areas, you are the first person I have ever heard say you can have too much return.

thanks
 
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Old 08-15-12, 06:46 AM
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In a forced air system the manufacturer has designed his equipment to have a certain number of square inches of return air (the same as the area open to the machine's return) This is a designed opening to the blower system that is self modulating. The blower will only draw as much air as will flow through this opening. You can attach a four square foot return to it, but it will only draw in as much air as the blower is putting out to the supply ductwork. Restricting the air flow with smaller sq inch return, however is a problem, and will detrimentally affect the operation of the machine. Likewise, the supply ductwork must at least match the square inches of supply area at the machine (with allowances for duct friction losses) You can add all of the returns you desire, but remember, moving air takes the path of least resistance and your closest (shortest) runs will draw more return air than the farther runs. If you go to multiple returns, they should have in line dampers that you can lock to a certain position. Then have a guy with a bellometer check the system for supply/return air balance if you want it perfect.
 
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Old 08-15-12, 07:06 AM
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Thanks very much for your informative and detailed response.
 
 

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