Do I need bigger supply and return lines

[johngammel]

garage info:
1,000 sq. ft. block/stucco with 9 1/2' ceilings
Trane XR12 2TTR2030A R22 2.5 ton (30,000 BTU) A/C external unit
attic mounted air handler
3 supply lines using 8" I.D. flexible ducting to 7" x 11" ceiling mounted registers (3 x 50 = 150 sq. in.)
1 return line using 14" I.D. (likely) flexible ducting to 18" x 18" ceiling mounted register (153 sq. in.)
operating temps on a 93 degree sunny day - register @67 and unit discharge air @ 106

The unit just can't get the garage below about 83 degrees. The refrigerant level was checked some months ago and found to be correct. I have only used it on a scattered basis until now but it has turned too hot to be comfortable working on cars so I'm running it all day.

After some preliminary work I think that both the supply and return lines are under sized. Thoughts on my conclusions? If they are undersized what's the minimum sq. in. that I need?

 

[toyotadriver]

Need some more info.

What is the insulation level in the shop?

From looking at a chart, it looks like 2.5 tons should have about 1000 cfm. Your 18x18 grill should flow about 585 cfm so it does appear to me that you are starving your unit for return air. What does interest me though is if you are starving the unit for air, I would think that the air that comes out would be very cold...just not enough of it. But 67* isn't very cool for an AC unit.

Where is this located?


By the way, I'm not a professional HVAC guy. I'm a somewhat knowledgeable amateur. But, I have been able to diagnose an issue with a new HVAC system that my installer couldn't figure out.

 

[pseudorealityx]

The answer is yes... you need larger ductwork. We cannot provide you with the 'correct' number without additional information.

 

[truckman5000]

1- 8in flex at 20ft length is 200cfm.
2.5 ton unit needs 1,000 cfm
If the freon was "checked" you would have high discharge psi. With air-flow prob.
If you only have 3- 8in. runs, im surprised that you dont have problems, maybee a freeze stat, that short cycles the out door condenser??
Running this with the 2- above, is a answer for a compressor change every 3- years.

Take some pic's ove the area/ air-handler, and ill be able to help/ p.m. me

 

[johngammel]

The Trane is located on the east side of the garage which puts it in the shade later in the day and the entire evening. The garage has all interior sheet rock and lots of insulation in the ceiling. I live in Englewood which is SW FL so it's hot now every day. Usually high 80s by 10:00 AM. To clarify the 106 degree temp is on the outside unti.

My thought is to buy a 25 foot box of 12" flexible duct and install an additional 12" register box with just a very short elbow right next to the air handler and use most of the remainder of the 12" flexible duct to run a second return using another 12" register box as close to the front of the garage as I can get it.

I think I can get it done without passing out from the heat (I'm a senior citizen) by cutting the starting collars into the air handler and then running that while I work in the attic.

Sound like a workable plan?

 

[Mr onetwo]

Your biggest problem is using flex duct.You need larger metal trunk lines to and from the airhandler with short runs of flex to each outlet. Per SMACNA 5.23.31 "F- Connect air devices to low pressure ductwork with five-foot maximum length of flexible duct and provide with a Flex-Flow elbow support. "

 

[johngammel]

Here in Florida they use flex duct everywhere including new construction. You can't buy larger diameter sheet metal at the big box stores and the supply houses won't sell to someone not in the trades. So I'm stuck with using flex duct the largest of which I can buy at the big box store is 12".

 

[CNGsaves]

Are all those Supply and Return duct pipes/trunks both . . . . .
. . . . . SEALED . . . . . and . . . . INSULATED
in the Florida attic ???

If not, you're really just cooling the attic !!

 

[johngammel]

They are the insulated type. I haven't opened one up but I guess about 2" all the way around. The 12" that is sold locally is R6. I've reviewed the current ducting and it all appears to be adequate - no obvious rips or disconnects. This winter I'm going to put it on my schedule to do a more thorough review.

For now I'm just trying to get the garage so that I can get my '61 reassembled and back on the road in time for the fall car show season.

 

[Fixin'Stuff]

I think I can get it done without passing out from the heat (I'm a senior citizen) by cutting the starting collars into the air handler and then running that while I work in the attic.

Sound like a workable plan?

Plan your work to start around 6:30-7:00 AM. It's the coolest part of the day in the attic and you'll start to get some natural light from the soffit and roof vents as the sun starts to rise. Usually by 8:30-9:00 it will start to get pretty warm up there.