Thanks for your input kaseki. I wish I were an engineer and could give an actual figure on how leaky the house is, best I can say is VERY :). Along with the hole out the roof for the swamp cooler there are also (6) 8"X5" openings to the crawl space. The other gas combustion appliances (boiler and H2O heater) are in the utility room which accesses the crawl space. The utility room is also below the kitchen. As for the source of their make up air I'm unsure... kinda makes me wish I'd asked the tech. who installed the new boiler last year a lot more questions. So, thinking this through if we were to go with the 1200 cfm hood and connected a damper to a fresh air inlet (hole) to the outside and to nothing on the inside (as we have no forced air and therefore no ducting), the damper would open when I used the range vent and let in MUA for the time the range vent was in use, and close when it wasn't. Realistically, how much more air could it be pulling in than the 6 other holes in the crawl space and the one in the roof? hmmm. I'm probably missing something in my logic but it seems silly to have only 1 of 8 openings controlled unless it's absolutely necessary to have that 8th hole and it's in a location that I want to be able to shut is my thinking. Currently I have a non-functioning electric range with OTR MW recirculation hood (the catalyst for the whole remodel). Needless-to-say I'm excited to have proper range ventilation and want to do it right, but I'm starting to think that a damper for additional MAU might not be needed. I do know this, the 3 times a year my DH takes the time to get me a really good fire going, I'm sitting in front of it and am no where near the range. :)

You need a plastic vapour barrier OVER a concrete floor? I would have assumed there was a moisture barrier under the concrete, and that would suffice. Where I am, Interior British Columbia, basement floors are bare concrete, and if finished, have carpet and regular underlay, or some sort of hardwood or laminate flooring with some sort of underlayment... but nothing that would really comprise a true vapour barrier. A lot of the time, basement floor formwork is polystyrene, so it's insulated and moisture-proofed at the same time.

I suggest separate systems for the first and second floor. That is the best way to have even temperatures on each floor. It costs more up front, but you potentially have lower operating costs. You could zone the loft off the second floor system. However if you are going to be working 10 hours days with multiple pieces of equipment generating heat then spend the money on a mini split.

I have a crawl space. Vents should be open all the time, except for winter months (in cold areas) Air circulation is important. A good thick plastic sheeting should be properly applied to the dirt floor to keep moisture from underneath out of the crawl space. No insualtion under the house itself, unless you have done other special work to keep it a conditioned space. Since up until several years ago, we had never had a crawl space, we thought about insulating the underside of the house, but, were told no, not a good idea by every insulation company we contacted. This is the second house with a crawl space we have owned now. It stays dry as a bone underneath, but, we also have proper drainage outside too.