Insulating Supply ducts
Insulating Supply ducts
(OP)
I would like to get some input on the subject of insulating supply ducts which are located in return air spaces, perticularly in multi story applications. I Have seen installations designed with no insulation on the supply ducts where the ceiling was opened to the decking on single story buildings. I tend to believe that would be a bit risky. However it seems to be a much more common to see supply ducts not insulated on lower floors of multi story buildings. I am not sure the IECC would even permit this type of installation any longer. Any thoughts would be greatly appreciated.
Thanks
Khllmrk
Thanks
Khllmrk





RE: Insulating Supply ducts
RE: Insulating Supply ducts
ASHRAE/IES Standard 90.1-1989, Energy Efficient Design of New Buildings Except Low-Rise Residential Buildings
Question 1: Does section 9.4.8.3 require duct insulation for a cooling supply air duct conveying air at a design temperature of 56EF where the duct is located within a ceiling return air plenum with a temperature of 77EF?
Answer: Yes. In the example given, insulation with a minimum R-value of 4 would be required since the supply air to ambient air temperature difference is between 15EF and 40EF.
RE: Insulating Supply ducts
A 55°F supply system is designed for light office work to maintain a 72°F db, 50% maximum summer humidity level. The uninsulated 55°F air duct should avoid condensation because the dew point is 52°F under the design conditions.
Five years later, the company does well, so there are more office machines and more people and the system returns 75°F, 60% humidity air during design conditions. The 60°F dew point air would then make the supply ducts sweat, leading to mold and other problems.
I would agree with your thought that it would be risky. The only supply ducts I've seen intentionally not insulated (inside or outside plenums) only appeared that way - they were actually lined on the inside.
RE: Insulating Supply ducts
It takes only the thinnest layer of duct wrap to prevent condensation under these circumstances. I believe that the added cost for an insulated supply is well worth the knowledge that you are not creating moisture problems in your plenum.
---KenRad
RE: Insulating Supply ducts