Shop cooling question. Insulating a portable A/C exhaust duct good idea or bad?

[David Hostetler]

The title to the thread pretty much sums up the question, but let me give some background here. I have a 13.5K BTU portable A/C unit, ducted via 2 5" dryer vent type louvered vents. They are attached to the A/C unit via the OEM duct hoses. The intake side is no big deal, but the exhaust side gets quite hot. I haven't measured it so I am not sure exactly HOW hot, but it is not comfortable to touch it. I am sure that it is dumping heat right back into the air it just cooled. So I have been thinking about insulating the duct. My questions are...

#1. Is insulating the exhaust duct in particular of a portable A/C unit a good idea or not?

#2. If it is a good idea, not likely to harm anything, what can I use to insulate it, and how can I keep the insulating media in place?

[Dave Gaul]

#1 I can't think of how it could be a bad idea.

#2 I'm pretty sure you can buy insulated flexible duct tubing at the home centers.

[David Hostetler]

I was actually wanting to insulate the existing ducting. I do have some 5" flex insulated duct from an old AC project, but I am not real confident how durable it would be in the shop... And I am not certain how to connect it to these goofy fittings from the AC MFG...

[David G Baker]

David,
Run your existing ducting inside of larger insulated flex ducting, that way you have no fitting problem.

[Charles Lent]

Having at one time been in the HVAC business, I see no reason why you can't insulate either or both of those flexible ducts as heavily as you want to, but don't restrict the inside diameter in any way while doing it. The insulation needs to be on the outside of the existing flex duct and then a cover needs to go over the insulation to protect it. The latest way to install insulated round ducting for heating/cooling is to use a flexible insulated duct product that is a wire coil spring wrapped with fiberglass and covered both inside and out with plastic. 10' lengths of this come compressed into 14" packages that stretch to 10' when opened and they typically have a 6.2 insulation rating. Different sizes of these are used depending on the application. I wish they were available 40 years ago. Try an HVAC distributor or a local HVAC contractor near you to find some.

Charley

[David G Baker]

Charles L,
Yea, that is what I was talking about.

[David Hostetler]

Sounds like a winner of an idea. I am thinking 6" insulated flex duct should easily slip over my 5" OEM lines. I am actually starting to think that I should insulate the intake side as well, just to make sure thermal transfer happens in the right place for maximum efficiency... Home Depot locally carries insulated flex duct in even sized (4, 6, 8" etc...)

[David Hostetler]

Just a little update... I wrapped the exhaust side with an old fleece blanket. I kicked the ax on at 90 degrees. Within 20 minutes tube temp was down to 82. An improvement for sure...