Navien is a well established manufacturer with a good reputation world wide. I see them extensively used in commercially designed residential applications where many multiple boilers are installed providing staged capacity and redundancy. Are you aware of any class action law suits against Navien that have been successful? How would you know whether the ‘terrible reputation’ is the result of ‘terrible installation' or not? We know the definition of ‘insanity’. Doing the same thing the same way repeatedly and expecting a different outcome. That is what I expect is going on. Modern hydronics consists of 2-discreet component systems that each have to be designed and tuned for maximum efficiency with the distribution system also designed and tuned for comfort and then mated to each other. This is likely what’s not happening with the failures you’re eluding to. Something else is happening there to cause these failure, like a poorly designed distribution systems that results in low efficiency, short cycling, corrosive chemistry in flue gases or heat exchangers, improper ∆T between supply & return fluids, improper selection or setup of circulators, buffer tanks or (no) hydraulic separators, lack of proper controls, programming and monitoring, as just a few examples. Replacement ‘conditioned’ pre-mixed system fluids can be stored in liquid reservoirs feeds with low-level monitor alerts to ensure replacement fluids are of the right, non-corrosive chemistry. The days of straight up tap water as a replacement fluid is long gone unless you like corrosion, scale and expensive service calls. Yes, if serious algebra is part of basic arithmetic, then that’s all that’s needed. If California is doing something else - that’s just fine! IMPO SR

So what floor is the condensation on now? I wonder if you should try and put the drywallers off, and fashion some sort of skirt above the wet spot around the pipe - doesn't have to be pretty, just a bandage of paper towels or something, so you can confirm the water's not coming from above. I don't think condensation is out of the question, and of course it'll be on the outside of the pipe... I'm not familiar with radon pipes, presumably it's a vent - is it a sub-floor vent? Does it vent an uninsulated area, ie below your basement floor slab or something? If cool air is entering the pipe, either from below - or, don't forget, it's open at the top - some condensation may be expected, since it's just a cold surface, and any cold surface will attract condensation. If the wall's closed up, assuming there's no leak, this condensation may continue somewhat, although once the wall's closed up, the supply of moisture will be somewhat limited (depending on where the moisture barrier is, inside or outside of the pipe.... Hopefully someone who knows more will chime in, but if you confirm it's condensation, maybe the answer is (providing it's not against the code) to insulate the pipe, I just saw some combination foil/foam pipe insulation that'd be ideal.

No issues at all with the T1 heat pump, nothing is exhausted to the air. There is very very little heat that is pumped out during a cycle which comes out the bottom of the dryer (if you have it stacked and have the drawer you will notice the contents of the drawer are slightly warm). From a lint perspective, when you scrape the two lint filters after a cycle some may go airborne (as with any dryer) but it's very little. I think you might have seen a Miele vented dryer that was vented inside into an 'indoor dryer vent trap'. These you have to fill with water to try to trap some lint from the exhaust and there will be lint all over your walls if you don't keep up with it.

The ceiling above the crawlspace is the bottom of the first floor. The warm moist air in the crawl space will rise up into to house if there is no vapor barrier to stop it. I would expect a three year old house to have tight windows and doors. The crawl space might be a source of the excess moisture in the house. What size is the AC? I would think a 2.5 ton single stage, or 3 ton 2-stage AC would be sufficient for a newly constructed 1749 sq. foot single story house. Did the builder provide a load calculation? A 6-10 minute run time might be considered short cycling. How often does this happen in an hour and what is the outside temperature?