Sweating Ducts

[gallison]

We are running into several situations where the ductwork is sweating. We have checked all of the normal solutions. In these situations we suspect that the duct is oversized and the static is too low. does anyone know if bad duct design can cause sweating in a crawl space?

[udarrell]

We are running into several situations where the ductwork is sweating. We have checked all of the normal solutions. In these situations we suspect that the duct is oversized and the static is too low. does anyone know if bad duct design can cause sweating in a crawl space?
The ducts are below the dew point temperature.

They could require insulation, or increased Return-Air through the evaporator & more duct runs to raise the air temp & duct temp above the dew point.

Measure the crawl space temp & humidity, then determine its dew point at different conditions.

Is it the main or the branch runs, or everything, doing most of the sweating?
Figure out what the best solutions would be... :.02:

[Gunnery Sergeant Hartman]

Crawl space needs sealed and dehumidified...

[gallison]

It is the main trunk that is sweating. There is another system in the same crawl that is not having any problems. The trunk line does not decrease in size as branch lines come off and we are wondering if the slow moving low static air could cause the temperatures to be too low in the duct and result in sweating.

[sweatinit]

Gallison please not I am NOT a pro, not even close but I had some sweating ducts that were a result of the wrong piston being installed (http://hvac-talk.com/vbb/showthread.php?t=376342) I am sure there are a million other things that could cause it but that little piece of brass caused me a lot of headaches, just a thought, please take it with a grain of salt, again I am NOT A PRO

[sktn77a]

As a rule (for a given crawlspace temperature and dewpoint), sweating will be worse if your temperature differential is greater and/or your airflow is lower. If the two systems have the same ductwork insulation, then one of these may be your problem. If the ductwork that is sweating has lower R insulation, then that is probably your problem.