Adding return air vents


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Old 02-05-08, 11:23 AM
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Adding return air vents

Hey Everyone,
Since I'm going to have to replace my main ducts from my roof mounted unit, due to sheathing deterioration from the attic heat, I'm thinking it would be a good time to add some returns.

I have 16" 'grey' flex from the unit down to a framed in plenum in the hallway ceiling which feeds the majority of the registers (3 avg bedrooms, 2 baths, laundry room) just above the doors in each room. Also have a single 16" flex down to a framed in stud bay(?) for the return in the hallway at the floor below the plenum. Uses a 20 x 25 filter.

As it is, house stays pretty even, temp wise, as long as doors are open. Back 2 bedrooms a bit cooler in winter/ warmer in summer. If doors get closed (guests, painting, work in progress, etc), temp is much different.

I'm thinking of adding returns in 2 bedrooms, as we will be opening a wall between kitchen and 3rd bedroom, and rest of house is very open floorpan. Thinking 8" duct with filter returns. Supplies off the plenum in those rooms are 7" or 8".

My questions are....

How do I tap into the main 16" flex return

Is the add-on duct size adequate or maybe too much? The rooms aren't that big (12 x 12)

The returns have to be located in the ceiling, unfortunately. Where approx should they be located in relation to the supplies?

More details available if requested.

Thanks for any thoughts.
 
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Old 02-05-08, 11:32 AM
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Wink

The first and main thing we need is what is the size of the unit??? how many tons??and what CFM are you waoking at ???
A 16" flex is good for a 2 Ton unit or tight for a 2 1/2 ton
Now yes you can add returns to a unit. It is best to have that cold air 16" going into a ductboard box and the new cold air returns going into that. If they have their own filters Id run them back to the units cold air return at the unit.
 
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Old 02-05-08, 12:04 PM
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Ahhhh Ed, knew I'd see you

Its a Lennox GCS16R-411-100-1P, but don't know if that will give the info you need. Would have to go up on the roof for more info, can't find my notes right now. I'll be checking it out soon. BTW 1600 sf rancher

After my first post, I realized you can't tap directly into the flex (Duhhhh).

Because of the location where the return attaches to the wall bay, I'd need to build the ductboard box and put it directly beneath the unit. Framing support for it would be no problem. Would that work?

Any thoughts on the return location? I know low in the wall would be better, but thats not an option. So, ceiling mount, but same wall opposite end? or diagonal from supply?
 
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Old 02-06-08, 07:07 AM
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OK, found my spec sheet. Not sure which info gives the tonnage for the cooling. 34,400 BtuH?
 
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Old 02-08-08, 08:48 AM
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Anyone else care to comment? Plan on buying my supplies in a week or so.

Thx
 
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Old 02-08-08, 05:45 PM
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Returns near (or in) the ceiling are okay because the hotter hair will be at the ceiling level. Place the returns as far from the supply as possible.

Rule of thumb is that the total area of the returns should be 1-1/4 to 1-1/2 times the total area of the supply.


One ton of cooling is 12,000BTUs so your unit is just shy of 2-1/2 tons.
 
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Old 02-08-08, 07:22 PM
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By-pass Return Air

to keep from cutting into your flex you may want to consider installing by-pass vents. If the rooms share a hall between them you could put a larger vent in the hall and run two smaller vents from the bedrooms to the larger one, this should help your air circulation when doors are shut and may be easier. These can be installed anywhere convenient in the ceiling and the air is not pulled out of the room if placed to close to a supply vent.
 
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Old 02-08-08, 07:55 PM
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thx furd and vj that answered some ?'s and gave me some ideas.
 
 

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