Hi Richard,
This is the response I got back from the Air Diffusion Council and based on it, resting the duct against the side of an IC rated recessed light fixture *MAY* be acceptable. Note, though, that in my previous response I brought up the issue about using the recessed light fixture (of any type) for support would not be allowed, so the duct *laying on* the recessed light fixture would be a problem.
The exterior of the flexible duct has been tested to a continuous temperature of 125°F, and should be able to sustain a typical attic temperature of around 140°F as the outer covering "will start to soften around 200°F".
Also, if the recessed light fixture is not an IC rated can, the flexible duct is considered to be combustible material and as such is required to maintain the same 3 inch clearance from the recessed light fixture as all other combustible material.
Hopefully this will help finish filling in the blanks.
Codeman
(response from the Air Diffusion Council is below)
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Hello Jerry,
As a member of the ADC engineering committee, I’ve been asked to address your questions.
Flex duct is considered a combustible material in terms of clearance to heat producing/transferring devices. Any required clearance to a device must be maintained with flex duct as well.
Regarding flex duct temperature capabilities, UL181 has a high temperature test that puts 265°F air on the interior and maintains the exterior at 125°F. Therefore, any listed air duct can pass that test. However, 250° objects are going to be a problem for the vapor barrier of most flexible ducts. I don’t know of any published maximum temperature for the exterior of flex ducts since they are not intended to be close to anything hotter than an attic might climb to in the middle of summer. However, I can tell you that polyethylene will start to soften around 200°F. Any item that could reach or exceed 200°F should of course be avoided. I believe that IC rated fixtures would cut off well below this temperature. However, non-IC rated fixtures likely would cause problems, depending on their design and the bulb chosen. The cautions from the light fixture manufacturer should be heeded.
I hope this helps.
Russ Verbrugge
Senior Product Engineer
Hart & Cooley, Inc.
Grand Rapids, MI 49512
Russ.Verbrugge@hartcool.com~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~