Read though one of his post , unvented crawl space ? unvented attic? Us Yanks would have our licenses torn to pieces if we even said such an atrocity :D

My attic is unvented - sprayfoam is applied under sheathing - works well. I've measured temp under shingles at 165 (in October!) but attic stays <90, so ducts up there gain little heat and there aren't bugs and cobwebs and dust from outdoors.

Inspector saw and admired sprayfoam - no worries.

I've read that sealed and insulated crawl spaces are slowly gaining acceptance as well.

In our neck of the woods, the inspectors are perfectly fine with tight crawl spaces. I always recommend it. Why couldn't you do a tight crawl space if you can do a basement?

My response would be moisture ( if it enters ) a crawl space often is not entered for years at a time . and any one with confined space training would be very weary about entering an unvented confined space especialy if there is combustion in the home . gas , refrigerent , carbon monoxide all will collect in an unvented crawl space . The code issue up here is moisture
not to mention the sileint kill RADON
Now as I just read you can have a sealed crawl space ( not realy ) it shall be equiped with its own heat source set to maintain at least 55 degrees , it must be equiped with a dehumidification system to maintain no more then 60% RH and it must be vented to the living space 1ft sq /1500ft sq
I have to imagine the savings are deminished greatly  by heating and dehumidifying the space , not to mention inflitration of 55 degree air .

http://solar1.mech.unsw.edu.au/glm/papers/anderson_melb03.pdf


In the introduction 3rd or 4th paragraph it states cop decrease as much as 5% with dry air ( could it be so engineer are these guys reputible? )

As a side note I do NOT by any means endorse over humidification ever , dry skin is nothing if your trading it off for mold
depending on you cold surfaces in the home and other things like carpet . A pro should set up your system and offer recomendations on settings.

Also inspit of this thread Im not an humidifier nut , just a normal ol' effeciency nut

I don't disagree with the idea of somewhat conditioning a sealed crawl space - that way it stays mold free. Dryness also keeps down insect infestations as well. Any ductwork in the crawl will benefit from being in the conditioned space as well.

The 5% improvement in an air source heat pump water heater with a wet coil isn't surprising - it probably has more to do with the improvement in conductivity that drops of water on the fins impart - they protrude into the airstream and ensure that the airstream is at or below the wet bulb temperature. They may cause more turbulence as well.

A sealed crawl space done properly will be sealed.

First, it will start with a good layer of plastic. 8-10 mil, with good overlap (12" or so). This plastic will run up over the footer and up the wall a few inches. This is so that the next step will seal it.

Next is that foam is sprayed onto the foundation, effectively gluing the plastic to the wall/foam. The rim joists are also sprayed with foam.

Unless the crawl space is periodically flooded by high water table (why build there anyway, then?), this crawl space won't gather any moisture from the ground. . If water table may be an issue, a french drain should be used, anyway.

It may be an option to look into to put a sump pump in, too, in case there is a washer, or dish washer, or bath tub, or burst line, etc. flood.