Community: Mechanicals

I work with a non-profit building small, affordable houses in climate zone 4A. We have tried a few different methods of sealed/ conditioned crawls, but I am interested in finding the best, inexpensive method that will work long term for our buyers. So it needs to require minimal to zero maintenance or understanding of the science behind it for the people living in the house.

I am building an energy efficient 15 unit apartment building in MA this spring. We can either go natural gas or electric. I am considering going all electric since the MA Energy Code is so stringent and the heat load will be relatively small even though there are very cold temps at times. We might even put on solar panels for the house meter.
The electric units would take up much less space and I would rather not have to put in gas at all. I am not thrilled about electric hot water heaters but understand that the newer tankless units are much better.
Any input would be appreciated.

I'm building a new wood frame home with hot water baseboard heating in climate zone 6. The bathroom will have tile floors and I was thinking of using some electric resistance heat under the tile along with a baseboard hot water radiator in the bathroom. These electric systems are not inexpensive to install or operate so I am now considering simply running loops of Pex (the supply line to the bathroom radiator) between the joists to keep the tiles warm before the water in the line gets to the baseboard radiator.

I am contemplating some different HVAC options in Connecticut (zone 5). I currently have an 80% efficiency Carrier Infinity NG furnace (8 years old) that can be paired with a Carrier Greenspeed heat pump. I can do that for $11,400 before incentives, or replace my existing and dying 10 SEER AC unit with a new 16 SEER for $8,000.