On a frequent visitor to the vanguard website. About a year ago I had a Daikin inverter with 3 zones installed in my house. Today I noticed that there is condensate water collecting in the foil flex insulation of the bypass duct. I immediately got a bucket and put a hole in the jacket so I could drain it. I immediately shut off the static pressure control damper so it will close air flow to the bypass damper. Also unfortunately I noticed heavy condensate on the outside of the Daikin furnace assembly. Typically where I live the dew point gets anywhere from 76 to 80° this time of year at night and the temperature stays around 80°. Lastly it is in an unconditioned attic with spray foam traditional ceiling joists insulation. Two questions if I keep the bypass dampers closed will the static pressure cause problems in my system? I am not certain about building or fire codes but can I insulate the outside of the furnace to avoid the sweating of the unit?

yes sir! See ducts all the time next to the roof deck. In many cases the duct works have holes in them from the roofing nails. Can you say leaky ducts!

Thoughts ? Suggestions ?

Ok, then a follow-on question: Would it make more sense to replace end-of-life flex duct (assume EOL is around the warranty length) that was installed in a schetchy way with interior hard ducting (i.e., like new construction) rather than either fixing the old (and possibly have it fail shortly after) or tearing out the old flex duct and installing new?

Yep. My townhouse is like that. All of the ducts are sandwiched between the roof deck and cathedral ceiling and then snake down between the studs of exterior walls to reach ground floor ceiling. I’m sure some of them have puncture marks from the re-roof a couple of years ago.

For 20 years I’ve been praying that house would get struck by lightning or have a huge tree fall on it.

David: Both good questions. Yes, before cutting a piece of flex to shorten and tighten it, it’s a good idea to check its condition. Replacing it with a new piece of flex will be harder—sometimes much harder—than just dealing with one end, so that might push it out of the DIY category for some people and in some situations.

Regarding panned joist returns, I didn’t mention that one because doing it properly would be beyond DIY skill level in my opinion. But of course, they could slather mastic all over the outside and get it as sealed up as possible.

Lee: Hear, hear! There are definitely better ways to spend your money, and fixing duct problems is one of the best.