View Full Version : no air at end of trunk!!??
02-28-2011, 08:31 AM
16X8 duct run with 13 6 inch runs and a 2000 cfm fan but no air comes out the last 4 runs ...duct reduced to 10 inch round at the last 6 feet (to get around an ill placed stairwell) then opens into a 12x8 to get last 4 registers...this is the smallest zone in a 3 zone infinity system....tell me the answer to this illogical consequence.:gah:http://hvac-talk.com/vbb/images/smilies/gah.gif
02-28-2011, 08:34 AM
Too many runs off of an undersized trunk.
02-28-2011, 11:53 AM
If your duct is insulated on the inside, you are way under sized. Sounds like too much SP. What about your return air? I'll be willing to bet your total static pressure across the blower is well over the .5 rating. Get your manometer out and check.
02-28-2011, 12:31 PM
I can bring the 10" duct back to the 16x8 trunk increase the first five feet to 20" and attach the 10 incher to that twenty inch section...this is a screwy deal cause 7 runs are not even supposed to be there....the owner insisted on more for his garage and a little shop area that is totally isolated....static is .8 on high. fan this is a Carrier Infinity and has a gazillion settings:censored:
02-28-2011, 02:13 PM
running duct registers into a garage?
Off-gassing is an issue.
02-28-2011, 02:48 PM
I assume that the 16"X8" duct goes one way and some duct goes another?
If all you have is the 16"X8" going one way, I'm surprised your ESP isn't higher.
But back to why you're not getting any air; too many supplies. The duct can handle about 600 cfm and you have 1300 cfm of supplies. It doesn't add up.
02-28-2011, 04:40 PM
When you say no air do you actually mean no air or only a little air? If you mean no air on the same duct as the others that are getting air I would check to see if the four in question are even cut in, or if the duct is lined, if the liner was cut out. Or if a damper is shut. Is that .8 static only when that zone is on or when all three are open ... if they are opening. Have the Infinity controls been set up by someone who knows how?
02-28-2011, 05:08 PM
if you have ductwork in a garage, your screwed from the start.
02-28-2011, 06:05 PM
you don't say how long the over-all length of supply trunk is.
I have run 70' of supply trunk with two 7" heat runs 2' from the end and both registered had 140cfm. All registers had proper air flow. the return truck was 40' of 20x10 on either side of the supply (double cold air drops on either side of the furnace)
It was one of my better design jobs :grin2:
Btw, all my duct work is custom made, I don't use "factory" duct, from Gray metal or Acme
03-01-2011, 08:41 AM
DUCT IS TOO SMALL! Not too hard to figure out. You design this system?
03-01-2011, 06:38 PM
A garage isn't allowed to be on the same duct system as the house. So is the home owner aware that its a code violation, and won't past an inspection.
03-11-2011, 01:13 PM
Get a bigger Duct------Way under sized-------Static at the coil has got to be more than .80. If this is a correct reading get back in the attic space and repair the blown out or split duct that exist in that space.:gah::cheers:
03-11-2011, 01:26 PM
In the install process when the infinity sets up the airflow for each zone it will tell you what the external static is total and for each zone.
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