air handler in a small closet

[edwardh1]

From: edwardh1 Apr-29 1:05 pm

To: ALL (1 of 1)

73089.1

My Heat pump air handler is in a small closet . One wall of the closet has the filter grill in it, so the closet is under negative pressure as the air handler is open at the bottom and just sucks air from the closet.

The air handler top when the air discharges is connecetd to a big flex duct that goes up into the attic (thru the sheetrock ceiling of the closet).

When I moved in the area around the flex duct was a rough opening bigger than the flex duct- so there was basically a hole around the flex duct into the attic so when the unit ran it sucked hot or cold air from the attic down into the closet- a big energy drain- I have stuffed insulation around it and foamed it.

If I have the unit replaced - its old- what is the professional way to avoid this hole and avoild the "we'l put caulk around it solution- is there one? A flex duct sized sheetmetal pipe with a flange?

[Guest ahammer48]

Flexible duct work is a killer on air flow due to the ribbing. The air hits the ribbing and slows down to a crawl. The best solution if you can afford it would be to come off the A/H with hard(sheetmetal) duct up into the attic. Where it passes thru the sheetrock into the attic from the closet a collar(flange) can be made to go around the duct and attach to the sheetrock in the closet. That should eliminate the air leakage from the attic down into the closet.

Up in the attic if you can afford it span the entire length of the house with sheetmetal duct and then use flex for your tap offs to the individual rooms. Flex duct runs should never be over 6 foot long due to the airflow problem I mentioned.

If all of this is to much then yes, come off the A/H with sheetmetal. Have a collar(flange) made up and then up in the attic re-attach the exsisting flex duct.

Good luck

[edwardh1]

Thanks- the sheetmetal section with a collar is a good idea.

About flex duct - no problem if sized right- 95% of all the new homes regardless of price in my city are flex- sheetmetal has died 10 years ago.

[Guest ahammer48]

I have to be honest with you Ed. I do industrial HVAC, not homes. On my jobs, all duct work, even in small office buildings(2 stories) is sheetmetal. The reason is the smooth walls of the sheetmetal allow the full CFM(cubic feet per minute) and velocity of air to flow. Granted there is some lose even with SM.

I don't know what the residential building codes are, but in industry flex runs can be no longer then 6 ft here in NM. It seems to me that they would have to oversize alot to get proper CFM, but then you'd lose velocity so the air would just kinda fall out of your registers. Remember, flex is awhole lot cheaper then SM. nThats the main reason builders use it.

If the house is small (1600 sq/ft or less, not including garage), then I guess flex would be OK cause the runs aren't very long.Thats the main point. How long is that longest duct run?? Are there gonna be some turns?? All 1 story or 2?? 

If its  simple --run the flex down the middle of the attic and tap off to a few rooms-- then you should be ok. If your going over 25 ft, I'd think twice. 

If its larger then that then, if I could afford it, SM would be my 1st choice. 

Hope that helps.