[js.craig]

Hi. I need some advice. I bought a new heat pump last year. It's s 3 ton unit. It doesn't cool my house below 78 degrees. I had someone look at it. They are telling me 90% of my home cooling problems is the duct work. He said he would remove the trunk lines and rectangular shaped duct work and build a 4ft long box off the air carrier and run the flex tubing diretcly to the box. I think I can do this myself, but was wondering the complete deminsions. Height, Length, and Width? Any advice would be great.

Thanks,

Jeff

 

[beenthere]

What size is the opening in the air handler.

 

[js.craig]

The opening is 11.5 inches wide, and 13 inches high. Should I build a long trunk to fit all 9 flex tubes? Any help would be great.

 

[beenthere]

I prefer to build the box a bit wider then the opening. A 4' long trunk is ok, but longer is better. How long will the flex runs be to the box? Long flex runs tend to reduce air flow.

 

[js.craig]

I can build the box longer no problem. I don't have any idea how wide or tall to build it. Some of my flex will be 15ft. The builder put the air carrier toward the back of my home in the attic. This makes the living room and kitchen hot. Very little air flow out of vents. Do you have any suggestions to increase air flow for the front on my home as well?

 

[Doc Holliday]

I can build the box longer no problem. I don't have any idea how wide or tall to build it. Some of my flex will be 15ft. The builder put the air carrier toward the back of my home in the attic. This makes the living room and kitchen hot. Very little air flow out of vents. Do you have any suggestions to increase air flow for the front on my home as well?

Can you take some pics and post them? Proper duct take off positioning on the plenum box is vital to air flow as well. You can also add dampers on the plenum right at the duct take off so if one or more rooms are receiving possibly more than adequate air and/or you simply don't need so much to said room(s) than you can close those dampers to produce more air flow through the other ducts.

 

[beenthere]

Transition from the air handler's opening to a 12X18, make it 6 to 8 foot long. The shorter the flex, the better. No harm in making it 12 foot long either.

Next, what size is your return?

 

[Marty S.]

8" flex runs?

 

[beenthere]

8" flex runs?

?????

 

[Marty S.]

Just wondering. Three tons and only 9 runs.

 

[beenthere]

Just wondering. Three tons and only 9 runs.

Surely your not impling that the supply runs could be too small. :laughing:

 

[alecmcmahon]

Im in the middle of doing a install in my home, i found this helpful

http://www.alabamahabitat.org/sustainable/Rules_and_Rules_of_Thumb_for_Duct_Systems.pdf

Size supply plenums to the flanged opening of the blower outlet,not to the extents of AHU cabinet

My opening was like 10x14 or something those lines, i made a transition to a 12x18 supply trunk

some pics

( keep in mind I am not a pro, this whole setup could be completely wrong and fubar, but it might give you a visual )

 

[beenthere]

Thats not a transition, thats a butt joint. Its a very turbulent joint, and generally should be avoided. A transition, would be when the duct angles out or in to the size of the next duck. If you redo yours, it will help with air flow.

By the pic, your first take off may or may not be far enough a way from the joint to allow the air to stabilize. I suggest you redo the butt joint to a transition.

The rest of your install judging by the pics is very clean looking.

 

[alecmcmahon]

Thats not a transition, thats a butt joint. Its a very turbulent joint, and generally should be avoided. A transition, would be when the duct angles out or in to the size of the next duck. If you redo yours, it will help with air flow.

By the pic, your first take off may or may not be far enough a way from the joint to allow the air to stabilize. I suggest you redo the butt joint to a transition.

The rest of your install judging by the pics is very clean looking.

Thank you for the suggestion beenthere, I will look into it.

If kept, will this just be a noisy joint with blowing air sounds?

And my first run off is 36" from end of AHU to the center of my first 8" run off, there is also another run off in the same location on the backside.


Also, is " Butt Joint " the proper term for it? My Google-Fu must be weak, I cant seem to find any information on the joint on my search.

Thanks.

 

[Doc Holliday]

Butt joint more refers to carpentry. http://en.wikipedia.org/wiki/Butt_joint

I think what BT might mean is those boxes are butted together verus being transitioned from one to the other.

I don't think that tape is meant for air leaks. From what I understand it is mainly used for insulating commercial metal duct, on the insulation itself and not on the metal.

 

[alecmcmahon]

Butt joint more refers to carpentry. http://en.wikipedia.org/wiki/Butt_joint

I think what BT might mean is those boxes are butted together verus being transitioned from one to the other.

I don't think that tape is meant for air leaks. From what I understand it is mainly used for insulating commercial metal duct, on the insulation itself and not on the metal.

Really? I always assumed they were directly for the metal.

I also Siliconed all my collars and major joints, then taped on top of that.

 

[Doc Holliday]

Really? I always assumed they were directly for the metal.

I also Siliconed all my collars and major joints, then taped on top of that.

Your's was the first time in my over a decade of seeing insulation tape used on metal connections. Nashua UL listed Foil tape, hardcast (foil grip)tape, hardcast aka duct sealant. One or the other by code.

Your system would not pass inspection down here but since you're doing it yourself I guess inspections are out of the question.

 

[alecmcmahon]

I see, upon closer inspection it looks like you be right... the tape around the collars off the main trunk started peeling and not holding too well, I peeled them off and applied duct sealant mastic, the flat seems on the corners are holding great, i could not peel them off even if i wanted too. I'll prob. go over them with the proper foil tape a few rows thick just for safe measure anyhow.

 

[beenthere]

A butt joint, is any joint that the pieces are just placed/butted together. Its a term often used in welding.

You said 36" from air handler to the center of the start collar. So by the pic, it looks like about 18" from the butt to the center of the start collar. it may have a poor air flow from those 2 runs then.

 

[alecmcmahon]

A butt joint, is any joint that the pieces are just placed/butted together. Its a term often used in welding.

You said 36" from air handler to the center of the start collar. So by the pic, it looks like about 18" from the butt to the center of the start collar. it may have a poor air flow from those 2 runs then.

How far should the first runs be away from the AHU ? If I decide to re-do the transition pc, i will be able to extend it further away.