These are "nutshell" answers since envelope issues are tough to diagnose over the internet. The HRV is an exchanger, but if your house is tight and your winter interior humidity is high, it'll exchange stale humid interior air for fresh dry exterior air while minimizing heat loss during the exchange. A blower door test is usually part of a more comprehensive analysis which could run a few hundred dollars. $200-$400 depending on the thoroughness of the inspection. If your house is excessively tight then it might make sense to install make-up air duct for the furnace. If you have an HVAC company out there, often times they'll do envelope and blower door tests. With all the "green" garbage going on, there are a lot of folks jumping on the bandwagon just as "energy consultants." If you're going to have work done, many companies will credit the cost of the blower door test and other analysis towards the cost of future modifications. Backtracking and peeking at the larger picture, basements can be a source of moisture vapor. Moisture vapor and maybe even liquid through rubble foundations, or vapor through poured concrete or block foundations. Think of it this way: You tightened up your house, which lessens moisture removal, but if your basement is a source of moisture vapor, it's still adding moisture vapor to the house. If it applies to you, a good thing to do is to minimize as best as you can air movement from the unconditioned basement into the conditioned living space above. Go in the basement and look up. Any gaps in the basement ceiling that lead into the house above (plumbing penetrations, electrical penetrations, hvac penetrations, etc) can be sealed with canned foam. It makes sense to do the same thing in the attic floor if the attic is unconditioned. The goal is to keep the conditioned air that you're paying to condition within the thermal envelope of the house. It's not a sexy job, mostly elbow grease, but walking and crawling around your house and shooting gaps with foam can have great effect. With those DIY cans of foam like Great Stuff, it's best to uncover the gaps first, then fill them all at once. Ling delays between trigger actuations can allow foam to cure in the nozzle.

mike -- Don't know that we will need a timer. It's just DH and I -- retired -- can remember to turn it off, I think. BTW, how long should it run after a bath or shower? energy rater -- The specs say the backdraft damper is within the 8" duct connection portion of the fan, not whether it faces in or out. I need to ask that they face it away from the fan itself, right? Or are you saying the damper should be not at the fan, but at the soffit? The bath is on the NW corner of the house. Air and moisture will go UP through the bathroom ceiling into the fan, ACROSS about ten feet of attic floor, then out a West soffit. Is it at the soffit that you want metal-flex flaps? Does moisture acclumlate there? Drip outside the exterior wall? (Yeah, where DOES the water go?) I see round aluminum-looking flex-ducting in the attic. Is that what I should expect to see on this install -- not hard metal ducting like a forced air furnace? Is this capacity appropriate? I want to eliminate excess moisture, but don't want to be taking baths or showers in a wind tunnel! (It is meant to run *while* one bathes and a short while afterwards, right?) Is a sone rating of 1.7 good? Is Broan a good brand? This installer is also going to correct three other, smaller bathroom exhaust fan ducts that now empty INTO the attic instead of outdoors. Price is $900 all in for Broan unit and all work. He says it will take about four hours. We are north of Chicago in a high-*address tax*-suburb, as my DH terms it. Thanks so much for your time and trouble. Much appreciated. I'm probably overly concerned, but we keep finding faults (like these fan exhausts) in a house that passed city inspection when it was built only 10 years ago. I'm sure it was not code to vent into an attic!

No attic access? No way to get up there at all? Not a ceiling scuttle hidden in a closet some where?Agree with Joe, we can give guidelines to install the fan, but the wiring is the issue. Do you have a plan for wiring the fan? Probably the easiest would be to extend the wiring from the bathroom ceiling light. Attic access would make it a heckuva lot easier. But barring any out of the ordinary attic framing, extending the ceiling light circuit could be done with a couple of fishing tapes. Is that an option? And then...there are wall exhaust fans. Again, depending on location, electrical would be an issue.

Yes the plan is vent through the roof. My question is since I'm getting a new roof, should I create two openings in the roof and each connected to its own pvc pipe back to the 2 exhaust fans? Or should I use something like fantech where the fan is sitting in the attic and I'll need one opening in the roof? Supposedly it makes it quieter since fan is in the attic but I know the panasonic units are also fairly quiet. I'm looking for something that will last a long time https://www.amazon.com/Fantech-Premium-Bathroom-Exhaust-Vent/dp/B01COPXHVW?th=1