We live Northwest of Minneapolis (6a/boardering on 7a) in a 2 story + full basement house (2,500 sqft) built in 1998 (2×6 walls/R19 fiberglass, vinyl siding, Tyvec, Built Right Sheathing, so-so all vinyl windows) that has winter moisture problems (condensation on windows, mold, freezing). During our pre-sale inspection, we noticed moisture on the 2nd floor windows and found that two upstairs bath fans were not attached to bottom of the roof deck, the insulated ducts/flanges were laying in the insulation (thankfully the flanges were taped closed). We attributed the moisture to this and shortly after purchasing the house, reattached the ducting.

A couple years have past and we have continued to have excessive moisture on our windows all winter. I recently started running my furnace fan 24×7 to help address the issue (and was horrified when i received our last electricity bill – we have a non-variable speed furnace fan) and have been keeping our blinds open during the day, which seems to have helped the window moisture substantially.

BUT – earlier today, i was cutting in a junction box on inside of an exterior wall in a stud cavity above an existing outlet and moved the insulation to find moisture/frost on the backside of the wall sheathing. Thankfully i couldn’t see any mold or material deterioration.

I’ve spent the last 8 hours reading (tons on GBA!) and am more confused than when i started with all of the opinions available to begin better regulating the moisture and ventilating our house. My wife and I have both had concerns about indoor air quality and are open to spending money to correct the problem(s), but we would really appreciate some advice on where to start, who to trust and what options would work best in our climate.

A couple other details:
– The two upper floor bath fans are the el cheapo $19.99 units. Would upgrading to something like a higher end Panasonic with rigid ducting (insulated, of course) be a good place to start?
– The fans are currently on toggle switches. I’ve found Leviton makes a moisture sensing ‘switch’ – are these worthwhile? Or maybe just a timer switch?
– One of the upper baths is in the center of the floor – about 50 sqft. Post shower, with the door closed, the room will still be moist/mirror fogged up, 30 minutes later with the fan running. I’m thinking i may need to undercut the door to get better air flow into this room in addition to upgrading the fan.
– There are a total of four people living in the house
– No existing HRV/ERV
– Given what i’ve read (Martin H. is outstanding) about connecting an HRV/ERV to our existing ducting and the ‘already built’ condition of our house, is an HRV even an option for us? Getting new duct work to the second story bathrooms/living spaces would require substantial disruption/re-working of our current layout. Or is this a case where doing SOMETHING is critical even if its not done perfectly?

I apologize in advance for being so long-winded – I’d really like to get moving in the right direction sooner rather than later.

Thanks
zack