I am in the middle of a residential construction project where they have just started putting in the HVAC system. I am talking to the installer about how important it is that the system be sealed well, that I want a blower door test once everything is finished, etc.

The topic comes around to how they are sealing the seams, particularly on the hardpipe and around the joints. He told me that the joints were screwed then taped using a UL 557 product. He said this worked well and that they try not to use mastic much because mastic takes too long to dry and that the insulation guys just end up pulling it off anyway when they put their insulation on. I went down in the crawlspace and sure enough all the seams that I could see were sealed with this tape. I would like to get your opinion of whether screwing then taping is enough or if I should insist on mastic. Thanks.