We noticed we had mold on our register grills due to one of our AC unit not draining anymore in the attic (water was ponding in the pan); we had a remediation company come out and they told us we needed to change the one unit and all the ducts; then we had to clean the ducts on the second unit and change the insulation in the vent registers; not cheap, to say the least. we ended up replacing the entire unit and all the ducts attached to that unit and we did the duct cleaning on the other unit. But we decided to replace the insulation on the vent registers ourselves. Unfortunately, to find out that we don't know where to find this type of insulation (3" wide); we googled and researched, but not much info on what type of insulation we need to use and where to find it. I went to an AC supply store and was told to get some "black" insulation (soft on one side with a harder film/felt on the other). The previous insulation was yellow with paper on one side. does anybody know if any insulation can be used for that purpose ? can this "black" insulation be used ? any input would be appreciated.

  • Are you maybe talking about insulated register boxes? The item commonly called the register is just the louvred grill that the air blows through. Some installations (I think mostly in refrigeration applications, at least in my area with temperate climate) use insulated boxes to which the duct and registers attach. Oct 31 '20 at 1:38
  • Wow could you provide a photo of the registers inside? Having water pool in the inside unit to some level is in every central air/heat system. Unless it was tested to be a toxic mold my opinion is a simple 3-5% hydrogen peroxide and water solution would have killed the mold and sterilized the system. I don’t use interior duct insulation but have treated systems that had plugged drains usually adding a high power black light after treating with a hydrogen peroxide fog into the duct and catching the excess with cheese cloth for the stronger solutions so it will not bleach the carpet or drapes
    – Ed Beal
    Oct 31 '20 at 5:27
  • I should also add I don’t use acid based coil cleaners they degrade the fins and aluminum tubing. But the trunk lines after the air handler can be fogged by adding a misting bar to create the fog I have done this on several homes that we’re unoccupied and the entire homes had black mold but it was not toxic there are thousands of mold species but only a small number are really toxic. These do require removal in most cases. But an example about 12-13 years ago we purchased a foreclosed house because 2 bedrooms had black mold no test was done, we did it was not toxic we got it 125k short ...
    – Ed Beal
    Oct 31 '20 at 5:41
  • so what i call the "register box" is the metal insulated box that ends at the end of the ducts and where air blows out into the room. The register box is covered by a "grill" type of cover where air blows out of. The insulation i am referring to that i am trying to replace is the insulation inside these boxes. the old one was yellow and the one i am offered is all black.
    – Jean
    Nov 1 '20 at 23:55
  • @ Ed Beal. we definitively had mold spots on these register grills. not all of them, but 4-5 of them. the remediation company said that the best was to replace ALL the ducts and registers (at least for the unit that had the issue) and unit by itself. But they also said the other system was probably compromised and suggested a duct cleaning and to replace all the insulalion in the register boxes too.
    – Jean
    Nov 1 '20 at 23:58

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