Enlarging my return grille/box


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Old 07-15-08, 09:57 AM
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Enlarging my return grille/box

Hello all, great site just joined.

Today a friend may have access to a return grille probably 18x30.

In my 1250 square foot house, the current return size is 12x30.

Having read some info. is it true a rule of thumb for standard size is multiplying your Air Handler tons by 144?

And to oversize it 180-200?

I have a 2.5 ton system that is less then 3 years old, and works well. Some other information...

The air handler sits in the open attic in the garage above the one and only return.

The ducting is old...very old, but works and does not leak.

By those previous rules I am at 360 square inches for my 12x30 return, which satisfies the standard i read elsewhere (2.5 tons X 144)

A 18x30 oversized change would put me at 540 square inches.

Basically during the hottest days my house has hot spots and stuggles to get under 77 or so farenheit, however this doesnt happen if i take the initiative to leave the thermostat low enough to keep it running all day.

Now i also must state that my windows are from the 1970's and im working on that upgrade, as it will by far be the most important, but i want to chat on the issue of upgrading my return anyways, a friend with an extremely similar house has a 18x24 return in his house, but its hard to compare our temp's really because he has great new windows.

Anyways before we go sawin' into my drywall to stick a huge return in i wanted to join up and chat about this issue with others!

Thanks for reading
 
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Old 07-15-08, 06:11 PM
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Return

You would be ahead of the game to add a second return in the warmer part of the house.
 
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Old 07-15-08, 09:19 PM
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Additional Return Air Grills

You might consider the great Idea's grady had and add a damper to the shortest return run - in order to force more return from the longest run - Maybe 60/40 return flow would about do it!
 
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Old 07-16-08, 09:03 PM
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You say the ductwork is old...very old. If it is original ductwork from the 70's it's probably leaking more than you think. Back then, they just slid metal pipe together with a couple of screws and did not seal the seams. They only wrapped the pipes to keep them from sweating.

If you have metal duct, open up the insulation and find a seam. If it is not sealed with mastic, it is leaking. Period.

Often systems in this era are leaking 40%+ air. This causes the home to go under negative pressure and suck in hot, humid dirty air from outside making it hard for many systems to keep up.
 
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Old 07-18-08, 09:24 AM
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Thank you for the responses!

Adding a second return would be great, but i havent seen it in the other numerous houses this size and model. I'll talk with my AC friends about it. Any more advice on this idea is welcomed please.

The ducting is not the metal pipes, but its the stiff older fiberglass tubing. It definitely needs replaced but ive manually checked all the seals and boxes myself and im not leaking...but I still want nice new flexible ducting it would be better.

I still can enlarge my return this weekend with a friend if i want to, just looking for possible negatives. Has anyone else gone by that 144 (standard) or 180+(oversized) multiplied by Tons of system formula?

Anyways I know its my windows that are the real problem anyways, but I get interested in learning as much as I can about my AC system, I will be doing the ducting myself this winter if i can get the money for the flex.

Oh also one friend keeps telling me i don't need to mastic my air handler...and it sits in the attic...im going to do it anyways, thoughts on this? Should i look more into adding a attic fan to relieve heat on the air handler? Ive considered this idea already but im not wild about cutting a hole in my roof since the roof is only 3 years old or so...but if its done right its done right...

Thank you in advance for any more responses
 
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Old 07-18-08, 10:49 AM
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Ducts

If the ducts appear to be in good shape, leave them alone. Ductboard will flow more air, size for size, than will flex.

Regardless if the other houses have multiple returns or not, I still believe a second return will help. In new construction we have to install returns in each room (except kitchen & bath).
 
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Old 07-19-08, 06:44 AM
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hmm it might be possible to add a ceiling return to the back room. i'll have a look at that part of the attic and my air handler with my AC friend.

thanks for another response Grady, oh and interesting about the ducts. in that case ill be checking their seals again and try not to worry about them.
 
 

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