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Discussion Starter · #1 ·
Hi!<br>great site, had a load test done not sure if correct, the tech even said at first I thought I made a mistake "never seen a 960 sq,ft home needs<br>5.8 tons of ac(heat pump)<br>The house is 960sq. ft, single level up on stilts,wood contruction<br>3 bedrooms, 1 23x47" window in each, 2 baths no windows,lv/dr/kitchen one big area open design, kitchen has 1 window, lv rm 6' sliding door, windows are 23" high x 18 lin ft, catherdral ceiling thru out,<br>the Roof, is 4x6 tongue/groove, one side shingles and the interior side<br>is the ceiling, no attic, no air space, by the NC ocean (Nags HD) the return vent (2) go into a pc of ductwork that is3' x 3' x 7' tall! the air handler hs one 12" sq. fan, single speed right now has 3 ton unit,<br>always seems to need more, think this tech is right, any thoughts<br>will be appreciated. thks!<br>
 

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When its 95 or hotter out side. What temp can the current 3 ton maintain?
 

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Discussion Starter · #3 ·
load - reply

Beenthere:
thanks for the reply, inside the house gets 80 - 85 with 2 ceiling fans running, ac runs non stop, at present the return duct is 12 x 12 about
6' long,(ductboard) at the bottom is a 14" round flex,90 deg. bend going into the air handler, tech advises to change to sheet metal and make it 12 x 16, it would pu 1260 cfm. thks:yes:
 

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14" flex is ok for 1.5 tons. 12X12 is ok 1.5 tons. So it seems you have a major return problem. What size is the return grille? 12X16 is ok for almost 2.5 tons.

12X20 would be much better for 3 tons, still a tad small, be it would work much better.
 

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Discussion Starter · #5 ·
load - reply

thanks for your time and efforts on this. the living room, dining room and kitchen are one open space, catherdral ceiling, approx 12' up
at the center beam there is one return facing the living room area
12 x14/16" then right around the corner next to this another return vent approx 20 x 24 give or take an inch. both go into the 12 x 12 ductboard return down to the 14" flex.:yes:
 

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Your return grilles are border line for 3 tons. A bit small for keeping the velocity down. But ok.

The return hold up is your return duct. If you can't enlarge the return duct in the wall. Add another return. It can be on the floor. Would need a separate return duct for it, can't be tied into the already too small one.
 

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Discussion Starter · #7 ·
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Beenthere: thanks, the existing return duct/stack is in the closet, approx ( I have room to expand it):yes:
41"wide x 18 deep, what would you rec as far as size, and should I get rid of the 14" flex 90 deg just before the air handler.thks in advance.
 

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Internal dimension. 12X22. Thus will give rough a velocity of 655 FPM. If you cn cut out the air handle to accept the 12X22 duct, using it would be much better then that under sized 14" flex.
 

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Discussion Starter · #9 ·
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Beenthere: do you suggest I make the return vents larger (have enough wall surface) if so what size, and you mean from the vents down to the air handler 12 x 22 all the way correct, thanks again upfront. what are your thoughts about that 5.8 tons suggestion,:yes:

If it makes a difference for you to know, the two return vents are on a wall corner both going into the same return 12 x 12 (ductboard return stack)
 

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The vents could be bigger. But they are not the main hold up. The duct is.

Yes, 12X22 all the way.

5.8 tons sounds a bit much. I think increasing the return will show you that 3 tons is very close to the size you need. With the construction you described.
 

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Discussion Starter · #11 ·
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Beenthere: thks again, trying not to be a bother, appreciate the input
just tired of all these know it alls and know nothing, I am a big fan of doing it right the first time, using the best materials and sleeping at night, not only on my own home but my clients as well. If making the vents larger will help the bottom line I can make them larger, just need to know the size, and would it make a big difference if I can only go 12x18", if not I will try to make it work, thanks again very much appreciate you spending this time today. thks!:)
 

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12X18 will be better then your current duct(I'm talking inside diameter).

If you can make your smaller return grille, 12X18, that will gt you down to a velocity of 300 FPM through the 2 return grilles.
 

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Discussion Starter · #13 ·
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Beenthere: thanks for staying on top of this with me. if I can go larger
on the smaller (than12x18) return vent should I, if so up to what size (I have plenty of wall space to work with) would it benefit me to try and do the 12x22, instead of the 12x18 return duct stack, is there that much difference to the end result. thks, hope your enjoying your Sunday.:) also the larger existing return vent should I make that larger also.
 

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If you can make the smaller vent atleast 12X18, that will work. That will give you a very low resistance to air flow in your return vents.

12X22 return duct is what you should have.
 

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Discussion Starter · #15 ·
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thks again: any concern about the existing air handler fan: looks like a 1/2 hp single speed, 12" squirrel round cage type, and like I explained
the 14" return flex round duct goes into the air handler but there are 2
boxes side by side, goes in one and then out the other to the trunk,
this unit is approx.2 1/2 x 3 x 7' tall, is this common. thks:)
 

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1/2HP is good for 1200 plus CFM. Standard air handler is about 20 to 28 inch deep, 17 to 24 inch wide, 44 inch high. not including return and supply plenums.
 

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Discussion Starter · #17 ·
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Beenthere: would it do any good if I outlined the existing trunk measurements and length to you or should I just execute what you have offered, once again don't want to bore you with too much detail,
but I sincerely appreciate all you have done in correcting & getting this job done right.
thks again.:)
 

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Discussion Starter · #18 ·
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Beenthere: maybe I missed this the return plenum is 24" x 20 x 48"
and the supply is approx 18" x 24" x 7' tall that goes into the trunk
with 11 runs, r6 flex, pulled tight and duct mastic sealed.:)
 

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Jut increasing the return as described should give you a big difference.

Long plenum. No problem with that though.

Guessing the 11 runs are all 6".
 

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Discussion Starter · #20 ·
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Beenthere: all runs are R6" flex, although code is not R8, might have to change, pulled tight and all takeoffs are the smooth type curved not 90deg. and all areas duct mastic, will let you know
what happens, thanks again stay in touch and have a great,safe,cool :)week.
 
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