Insulating sheet metal supply ducts in crawl

[jthatcher]

My Chicago-area mid-1960's 2,400 sq ft ranch home has sheet metal supply ducts in a 4 foot tall cemented crawl space. They are insulated by vinyl-backed fiberglass insulation, strapped by tape and twine around the duct.

The problem is that I am allergic to this insulation. Over the years, rodents and insects have made homes in portions of it, and I suspect some mold in it as well. Taking a sniff of the insulation sets off my classic allergy symptoms, sneezing, itching eyes, etc.

I want to get rid of it, but what do I replace it with?

Would a spray application of 2 pound closed-cell foam on the ducts be suitable? Does it handle the heat and cool surface temps of a supply duct?

Would wrapping foil-backed closed cell foam around the duct work?

Is there a material that resists water, rodents & insects, and performs well over the long-term on sheet metal supply ducts?(Fiberglass seems to welcome mold, insects and mice!)

I have had the supply and return ducts aerosealed and noticed a real difference in increased air volume and fewer hot/cold spots at the end of the house.

I have sealed the crawl space vents and use a dehumifier to humidity below 50%.

[ruud-man]

Ask your HVAC contractor about Reflectix bubble wrap. It is similar to the bubble packing used in shipping. You can get up to R6 and since it is plastic and foil it is water proof.

Since it is not standed fibers, it probably wouldn't attract rodents looking for nesting material.

Good luck...

[drk]

Fiber glass does not support mold growth! May try duct board but this is still fiber-glass so may not be any better. Another option is Imcoa (spelling?).

[Keith Lohr]

most likely the mold is on the outer jacket of the olds insulation, not in the fibreglass, caused by sweating over the years, have old insulation removed, seal the duct and re wrap with the newer foil; backed that is the the market, there is some low itch out there, i know of no foam based that is approved, I do wish there was. The bubble wrap with an air space of .75 inch will give a good r value, i do not think it is totally approved any more be cause of the r value, it does not promote growth , rodents and you can rub yourself with it and use the left over pieces as beer can coolers. i know of r-40 being achived on floor joist with it.

[cem-bsee]

SO,seal the crawl, insulate the walls except for the bottom 4- 8" so one can look for termites -- have pvc on earth, overlapped by 6+ inches.

I sure would not switch duct material!!!

what filters are you using? change to 5" thick pleated, change ea 3 months -- better would be to use Electronic Air Filters, but these require good & regular maintenance.

with metal ducts, how are you getting insulation into the airstream? you must have holes, poor junctions, etc --

apply HVAC mastic on ALL seams, joints, cracks, holes of HVAC boxes, etc --

recheck & seal the crawl against mice -- remove the food they need -- set traps --

new fiberglass insulation has a good vinyl jacket -- after the new is applied,
the closed cell foam would work, but will be $$$