For radon mitigation, you could consider an intermediate holding tank that you can flush air through to was the radon out. Alternatively, you can use a venturi, followed by two pumps and a chamber that you can hold at low pressure to off gas the dissolved gasses. It takes more energy, but it works as an in line process. If your water is as soft as I suspect it is, you could run it over an RO filter, which would remove all the radon, and you could use the reject water to flush toilets, or recycle some fraction of it.
Don't forget that in the US, gypsum outgases significant amounts of radon, as it contains traces of thorium. For very well sealed homes, gypsum is usually the primary source of radon, so you want to have a reasonable heat exchanger to turn over the air.
You can get European roll shutters here to help with insulation, and there are a few manufacturers that make low e glass/Ar/Kr sandwich glass for higher thermal ratings. If you really want insulation, shutters, and insulated drapes do a much better job than anything you can do by glazing alone, but you do have to open/close them. I once saw a house that had triple glazing, with a six inch space between the outer double glazing and the inner glass. At night, they blew styrofoam beads in, and sucked them out in the morning. I recall that they had to get the antistatic agents just right- both too much and too little gave them stray beads stuck to the glass. Great insulation though!
All the best,
Peter
