I do not understand what your contractor is planning. I can immediately think of several reasons why: --he doesn't understand what he's doing --he can't communicate what he's doing --you don't understand well enough to pass along his plans, or --I don't know enough to understand, but since others aren't following either, I'm going to hope that I know enough to help. Many things interact together in this whole picture, so maybe some oversimplification of the physics would help you understand better. Kaseki makes a vital point: "In any case, there is always MUA." Think of an empty plastic bottle. Seal your lips around the opening and suck in (through your mouth). What happens? If any homes had imploded, we would have seen it on the news!! In that scenario, we have a really powerful exhaust fan (you) relative to the strength of the construction (plastic), and the construction is perfectly sealed (bottle). Now change the bottle to glass. Because an exhaust fan would not be able to implode the house even if it were perfectly sealed (otherwise, you got bigger problems with your contractor than MUA!!). What happens? You (the exhaust fan) crap out. But, really no house is perfectly sealed. So, pretend that you have a glass bottle that has some really tiny holes in it. You suck hard; air comes into the tiny holes, but you have to work really hard. If you're really trying to clear something out of that bottle, it would work a lot better with some nice big holes. That's the open window part that you already understand. And if the hole/window is wide enough, most of the air will come in through the big hole rather than through the little ones. But, as you pointed out that air is going to be cold in January, so let's keep the window closed for now. In fact, to over-simplify again, let's just take the exhaust fan out of the picture for a bit. Let's just put you and a fire in a little room that's sealed up pretty tight. Now you're not cold:) That fire is burning oxygen from the room and producing carbon dioxide (not so good for the environment, but not too bad for us unless there's an awful lot; and actually you're doing the same thing, breathing in 02 and breathing out C02). As you and your little fire (mostly the greedy little fire) use the oxygen, Greedy starts getting less efficient, and he starts producing carbon MONoxide (CO). And you're going to forget about warm or cold and move through headache and nausea to oblivion. So, instead of the fire in your little room, let's have a woodstove. Nothing changes unless you provide both a chimney and intake air. (Typically, the intake is not associated with a woodstove. You'll just have to imagine harder to make that.) Now the woodstove has its air supply from the outside, and you have the inside air. (Since you go in and out once in a while, letting in fresh air, there's no problem with the amount of O2 you're using.) Modern HVAC systems are more like this "special" woodstove with its intake air. That keeps things much healthier and safer. Don't confuse that air with the air that gets blown through the ducts if you have forced-air heat though. You could add a blower system to the woodstove example. It blows inside air around the stove to warm it. The air for burning is still separate. So, we've taken care of the carbon monoxide issue, but what if our little room is a bathroom and it needs an exhaust fan. And the little room isn't perfectly sealed; it has a few holes here and there. But look, that hole that is letting in MUA when we run the fan is really close to the chimney, so there's smoke coming in. We can't catch a break! So we open a window that's not close to the chimney and open it wide enough that air flows pretty easily so that the exhaust fan pulls air from the window, not the smoky air near the chimney. So, it's cold again. And not only that but we never remember to open the window before turning on the fan or to close it until it gets really cold. Did I say I wanted this exhaust fan?! Some will argue that you really don't, but I'm not going to go there. I love my 600cfm hood. I rarely use it on full blast, but I haven't found the wok from storage yet. So, let's wire up a window opener/closer that opens and closes the window automatically when the fan is on. That would take care of part of the problem. I've found one example of that scenario. (A venting system, not literally a window open/closer) http://www.youtube.com/watch?v=NsSvMB9bJeE Here's another fact sheet I found. I think their images could really be improved by enlargement and color-coding! http://www.extension.umn.edu/distribution/housingandclothing/dk7284.html I did see some systems that would warm the air as it came in, but I don't even have the links because they totally didn't look like they were worth it. I hope oversimplifying and pulling apart some of the different pieces helps you (or someone) understand more. It seems there are few people out there who 'get' this. It's really straightforward at my house when there's a fire in the woodstove (mine's not special like the one in the scenario above!) and someone turns the range hood on high. The chimney starts providing really nasty makeup air!

Thanks for the replys, guys. Yeah, at first blush I thought it was pretty high, but the master bath accounts for about $13,900 of it. And as Bud noticed, there is a lot of cutting and detail work involved. And I forgot that in addition to the custom shower glass block walls, they are also replacing a small (maybe 3'x3') bathroom window with glass block. I'll definitely get another bid or two to compare, but glad to hear that it's not too far out of line. They said up front that they would not be the low bid, but they've been around 20+ years and came at the recommendation of my interior designer. BTW, she is just helping with design work on the whole project at an hourly rate, providing input and recommendations when I want, so I don't think she has a vested interest in recommending them. Her take is , sure, by all means get other bids, but hands down these guys will take care of you.

Now that you had the Manual J calculation done, you need to use Manual S to size and select the equipment. The systems are rated at 80* indoor dry bulb, so each degree lower you set your thermostat, you derate your system's sensible capacity through various calculations. It's possible that your 2.5-ton heat load may require a 3-ton system. What particular heat gain values did you obtain? Your contractor may not know how to do this, but it's important to have a properly-sized system. 4.5 tons sounds oversized... 3 tons or 2.5 tons sounds more in line.

Let's actually set this right. There are NOT three different methods of sound transmission, that is either way over-simplified or over-complicated, depending on the view that you want to take. Building designers have created a checklist to deal with building design and sound transmission. But that is because building designers have enough stuff to deal with without getting into the physics of mechanical waves when designing a building. There is exactly one method of sound transmission in buildings, on earth, in space, etc. Sound is a mechanical wave, or energy that travels through matter by disturbing it. More specifically even, it is the displacement of matter from its equilibrium position and that displacement as well as the rebounding of material is what moves sound through all matter, including air and walls, it is also the lack of matter to disturb that stops sound from moving through outer space. Sound is easy to understand as work, as sound encounters various forms of matter it expends effort to move through the material, even air, that is why decibels are lessened over distance. There are really only two ways to reduce sound, require more work and convert the work (technically there are three, but locate your basement in outer space seems a bit extreme). More mass means sound has to work harder to move the material, not unlike throwing a boulder compared to throwing a pebble. So one simple way to reduce sound transmission is to add more mass. The other is to convert sound to other forms of energy, usually heat energy. This is what resilient materials such as rubber and cork do. Think hitting someone with a bat versus hitting someone with a foam pole. ---------- Now all of this may seem immaterial to the discussion at hand but it really isn't. Building designers, especially when designing commercial buildings, have broken sound transmission into three very broad categories that they need to address in the design of a building. However, not every situation requires considering those things as they are presented, nor are those three things adequate in other situations. The final, and really more important point for homeowners, is the cost of effective design versus the cost of effective treatment. No one who actually works in theater installation and design really spends their day looking after these "three sound transmission characteristics" of building design. And no one creating sound isolation booths for recording studios would think addressing those three things are remotely adequate. I have both a home theater and a sound isolation booth in my house. There are thousands of installers, and hundreds of home theater and listening room designers who all use the same four steps for sound proofing: (1) sealing, (2) adding mass, (3) decoupling, and (4) dampening (note: that dampening is often separated into dampening and absorbing for ease of understanding). Any approach using these four steps, even in a cost effective manner, will adequately address sound transmission for most needs. Just to be clear it absolutely deals with airborne, flanking and impact transmission, it is well detailed in the material I directed the OP to. So any assertion that no one has dealt with that, is absolutely wrong. If you are building a sound isolation booth for a home recording studio, this is a good start, but by no means complete. However, you are going to have to get into specific attenuation at that point, at which time I would advise visiting the gearslutz.com or SoundonSound.com sites to get more information.