Outdoor Ductwork Insulation

[fcxdfm]

In the project I am working on, the existing outdoor air-conditiong (heating and cooling) duct was insulated with 1-1/2" fiberglass and aluminum vapor barrier jacket. However, the insulation at the bottom of the duct always got wet after rain, and already become loose now only after a couple of years new installation.

Has anyone had similar experience or any suggestion what's the best insulation and finish for the outdoor duct?

Thank you very much.

 

[GMcD]

Depends on how you define "best". From the sounds of your post, there was no re-covering on the thermal insulation wrap? IE: It was the plain foil finish exterior finish? The normal commercial level is one of two options:

Option 1: Exterior thermal wrap of min. 2" foil faced duct thermal wrap rigid board insulation, with a re-covering of 0.8mm aluminum sheet, lapped and sealed weatherproof with band clamps on 600mm centres.

Option 2: Internally lined duct insulation with the sheet metal duct as the outer surface, sealed and waterproofed.

Additional enhancements for institutional/better quality: Use option 2 with perforated liner on the insulation, and another exterior double wrap of bituminous/asphaltic coating impregnated fibreglass cloth (which could also apply to Option 1, as well). Then a re-covering with 0.8mm aluminum sheet for heat reflectance.

Yeah, expensive, but depends on how long you want this to last and what the energy losses are.

 

[fcxdfm]

Thanks, GMcD. I don't quite understand what "re-covering" means in Option 1. Is the re-covering aluminum sheet in Option 1 a separate layer from the thermo insulation?

Thanks again for help.

 

[AbbyNormal]

Its not cheap, but has a jacket similar to a roofing membrane, looks not bad

http://www.armacell.com/

http://www/armacell/ACwwwAttach.nsf/ansFiles/018PS-001-NA(NA).pdf/$File/018PS-001-NA(NA).pdf

 

[AbbyNormal]

go to armacell.com, look for armatuff

 

[GMcD]

FXDFM: yes- the re-covering is another sheath over top of the basic thermal wrap insulation. The light wieght flexible foil finish on the duct wrap is not a weather barrier no matter how well it's installed. You need to protect it with a real weather shield sheathing.

 

[fcxdfm]

Thanks both of you, GMcD and AbbyNormal.

 

[fcxdfm]

GMcD,

Could you please give me some manufacturers for the Option 2 with exterior enhancement?

Thanks again for help.

 

[GMcD]

There are no "manufacturers"- you have to call your local insulation contractor to do this. Asphaltic coverings and sheet aluminum are generally available from a variety of suppliers, but if this is specifically an insulation scope, then call your friendly neighborhood insulation contractor/supplier.

 

[fcxdfm]

GMcD, Thanks.