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.

Good that you realize the soffit issue with an exhaust vent. Either block off the soffit on each side from above, or could you possibly replace some of the vented soffit from below with solid material? There are higher quality roof vent hoods available. Fantech or American-Aldes are two sources that I've used. A roof vent can be added without damaging the integrity of the roof, just pay attention to the details and work carefully. Are the prevailing winds in your favor to limit snow accumulation in the proposed location? While your at it, consider adding a fan timer at the wall switch to insure the required ventilation time it takes to remove all the bath moisture.

If you're not trying to be 'defiant' of our reasoning, you're certainly trying to convert us to your way of thinking, and I don't think it's going to happen. Clearly you are not open to this idea, but others may at least consider it. So far the inspectors have not said anything. I consulted with two of them, the city engineer, my contractor, and fan suppliers before doing it. Firstly, I'm not going to contradict a building code, especially when there's no discernible logic (ok you disagree but fail to impart what actual advantage your system offers) or advantage to it. I'm not going to run to the library immediately to check the code, but I do get there reasonably often and will check. Again, the inspectors who are familiar with the code are okay with my installation. It could be that a fan is not required simply because I have ventilation into the room via the AC ducting and/or a window, so whether I have a fan in the room is my call. You mentioned your area does have mould issues....(as do all areas I guess) - your system is particularly unwise due to that. You are creating an unnecessary hazard. There seems to be no mold issues in the southwestern deserts or the Rocky Mountains. Our weather is heavily influenced by the Gulf of Mexico so we have humidity in the summer. I don't think it is going to be a problem but is certainly is an issue. Definitely not a hazard. You may even have created a fire hazard You're being alarmist. Explain to me how my house catches fire because the bathroom doesn't vent to the outside. There are a couple advantages to my system. First the fan draws only dry air into it. This keeps the wet dust from collecting on the fan blades and reducing the fan efficiency to near zero in a few months. Second, the fan is mounted 24 inches above the floor in the bedroom. If I need to clean it, which I doubt I will anytime soon, its right there at knee level instead of overhead on the ladder. Third, the air at 24 inches is blown up to the ceiling in the adjacent bathroom 9 inches down from the 9-foot ceiling. As you pointed out, warm air rises. My system blows relatively cool and dry air in a the ceiling height to thoroughly mix the warm/moist air with cool/dry air to get a more uniform air temp and moisture throughout the room. Fourth, air sucked into a fan is only sucked extremely locally. Without a few classes in aero I can't really get into how that works, but you'll notice the exhaust of a jet engine, or even an electric fan for that matter, can be felt much farther away from the blades than the intake air induction can be felt. You have to hold your hand directly to the back of a fan to feel any air intake at all. My system, even with a diffuser at the opening into the bathroom, blows the air into the room hard enough that I can feel it against the far wall, thus ensuring thorough air stirring and mixing. Fifthly (?), in the winter humidity is not a problem here. In the summer it can be if your AC is not properly designed. Mine seems to be but this room has not endured an entire summer. Actually spring is slightly worse for humidity because the humidity is up but the temps are not warm enough to trigger the thermostat. In the summer the AC runs day and night as the outside temps sometimes don't come down into the 80s for several days at a time. It's rather like 'vacuuming' or should I say reverse vacuuming, a room by blowing it all out with compressed air. There may be something about that system you like, but you're just taking the dust from one room (read humidity and bathroom smells) and spreading it throughout the rest of the house. And your vacuum system sucks dust in from outdoors and blows it all over the house. Which is better - the dust you already have indoors or the new dust your vacuum system is sucking in? I knew which fan you were talking about, but I was way off on my house fan power specs. Apologies. I'm not sure what model of blower I was looking at but mine is 3/4 horsepower - more like under 500 watts versus the 750 watts used by my directed fans. If one of my little fans wears out, I have backup. If my furnace fan wears out, it's a service call and a $12,000 AC system (mine is ready to be updated). Your bizarre method and logic may make the condensation evaporate more rapidly (or so you may think) because you are encouraging it to evaporate I guess into a larger area, however, that capacity would diminish over time, since the overall humidity will increase to the point of what is it - equilibrium? Where the air will hold no more moisture, and condensation begins to reform. This is where the structural damage sets in, mould forms and it becomes an unhealthy environment. From a heat transfer point of view, you need to watch your terms better to make that make sense but I think I know what you were trying to say. Still, the last sentence is the important one. The humidity increase from a shower is unlikely to saturate the 18,000 cubic feet of air in the house. However, this is exactly what I'll be looking for in the summer. These bathrooms are at the far end of the house. The concern is getting that air moved out of the confines of the bedrooms and out to the AC air intake in the living/dining rooms. I don't think it will be a problem in the summer with the AC on all the time, but we'll see. I'm more afraid of freezing my butt off in the shower with all that dry air coming in on me. I may have mentioned that I do not get any condensation in my bathroom now and I do not get any even when the fan is off. The reason for that is not clear. I'm working on the theory of massive tile heat sink where the moisture is actually condensing on the cooler tile but there is so much tile that I'm not noticing it. But there is never any fog in the bathroom and no condensation on the mirrors. Ceiling fans may have their drawbacks and I don't love cleaning them either, but I think I'd prefer them to a bunch of fans sitting around on the floors Clearly I'm not going to change your mind on that either but I have convinced several friends to use floor fans, especially in the winter, to mix the hot air at the ceiling with the cold air on the floor. Suddenly my short friends can get warm and my tall friends don't have cold feet. If the thermostat is at 5 feet off the floor and you're 5 feet tall, you live in a world where all the heat is above your head no matter what you set your thermostat to. But if you're six feet tall or taller, your face is always hot and your feet are always cold. With the little fan on the floor pointed at the ceiling behind the sofa, the air mixes in the entire room and everyone is comfortable. Everyone I demonstrate this effect to is amazed. A ceiling fan can be reversed and pointed at the ceiling, but you get into the problem again of the air intake being at 8 feet off the ground blowing air up to the 9-foot level. You really have to have the fan honking to blow that air to the walls and down. Then people seem to complain about the wind in the room. My little fans simply punch a localized hole in the thermal layers and mix them up. I keep ignoring the indelicate subject of bathroom odor, because that does not seem to be a problem in my household. It must be all the lard in the tamales down here ;-) Actually my wife pumps the veggies and fruit into us - I'm not a dietitian. Sorry I'm getting so wordy. Maybe this will stop now that we realize we're not going to change each other's minds.

As for fan-lights in the shower, it seems ineffective to try to remove water vapor laden air from the shower since most of it will condense on the walls before that can happen anyway. My goal is to remove humid air from the vanity area and allow fresh air drawn from the door undercut to reduce fogging of the mirror and window glass. The entire bathroom will eventually dry out if you use a fan with a built in timer and/or constant low speed feature like Panosonic's WhisperGreen series. I have yet to find a fan-light combination that performs as well as separate units. Here are my criteria: no CFL or LED lamps (LED inappropriate in a bathroom; CFL inappropriate in a house) Max sound rating .8 sone max grille size 13x13 flush with ceiling variable speed fan with timer Panasonic makes a recessed spotlight-fan combination (FV08VRL1) but it uses a CFL. I suppose a halogen PAR lamp could be substituted because the CFL is probably only needed to get an EnergyStar rating but I am not comfortable recommending it. To reduce fan noise it is important to reduce back-pressure by using larger metal ducts.