inspectorD

I agree with your reasons, and the heat exchanger can cause water issues in a home when it has a leak in it. I'm wondering if your co detector is working.
I am also trying figure out where the moisture is comming from, sometimes it is all things added up to create enough to cause the problem.
From here it is hard to tell you where to start, but the hrv is one solution to the exchange of air for the furnace, not the solution to the issue of the moisture.
The reason I say to get an expert in there is, you may be missing something you just do not recognize as an issue. Some folks seal up the house with insulation, new windows and weatherstripping...but do not seal the attic pull down staircase.
Try another set of eyes on the house, or call some folks with questions. Your local heat folks will come out to take a look at your issue if they think they can make a change, ask there for some advice.
To me this is a whole house solution that needs to be addressed, it may take more than just the hrv.

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Just My
Made in the

Quattro

Here's an interesting thing I just discovered. I have one of those little digital temp/RH meters, so I placed it in the basement last night. Then this afternoon I moved it up to the main floor bedroom, on the opposite side of the house from the basement location.

Here's what it read:

Basement: 61.7 degrees / 70% RH
Main floor bedroom: 68.4 degrees / 64-65% RH

This tells me that both air systems are basically the same! The basement probably only seems more damp because it's cooler.

inspectorD

This is why I suspect your furnace heat exchanger, I hope I am wrong and it is a accumulation of a couple of issues, but i would have it inspected by the heating Co.

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Just My
Made in the

Quattro

FYI - The second plastic test (in two locations) came up dry. So, I doubt the excess moisture is coming from the floor.

If the heat exchanger was bad, wouldn't our CO detector pick it up? It's only a couple months old. The previous one we had never went off either.

inspectorD

Could have 2 bad detectors, stranger things have happened.
Does your dryer vent to the outside?
If you can get into your furnace, a quich way to see if there may be leakage is to hold a mirror up to the exchanger area, if it fogs up, you have a leak.

Look at all the flue connections also, I have seen them broken at the unit or not even connected.

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Just My
Made in the

Quattro

If we were getting a lot of CO from the heat exchanger, I think we'd be pretty sick. The furnace has been on for over a week now (since overnight temps have been in the 30s).

The drier vents outside, and that is using rigid 4" duct. The vent cap outside is accessible, and when the drier is on, there is a solid stream of moist air coming out.

I will try the mirror trick on above the heat exchanger. There is an adjustable vent just above the evaporator I can remove and put in the mirror.

BTW- is there supposed to be condensate coming from the drip tube during heating? I'm not sure, but I think I saw a little this morning near the floor drain (which is where the drip tube ends up).

There is no flue, per se. it's high efficiency, so there's just the one 3" PVC exhaust (might be 2.5"). I can check the connection at the furnace.

Thanks for stickin' with me, D!