1) did you leave any air space between the insulation and the copper
tubing?

Yeah. There's about 3 inches of "air space" below the tubing and above the
insulation, and about 3 inches of "air space" above the tubing and the floor
above.

2) Soldering a copper line in an enclosed space is something I don't like to
do.

I agree with you. But then there are *dozens* of such joints all over the house
- basically everytime the copper pipe turns a corner, so I figured "what the
heck." (Famous last words, probably.)

You probably did okay with the copper, but for the future job, I consider
using PEX.

I did think about it, particularly after investingatng the Ultra-Fin system.
But I knew I wasn't going to have much heat in the pipes, and I thought the
copper would bleed the heat better than PEX. It still wasn't enough, and I had
to go with the mini-hot-water heater. Ah well. I may well use it upstairs in
the wife's bathroom, now that I know.

You also want to think about reducing the water pressure in the
system. I think the system will last longer.

Good idea. Thank you.

BTW, did you install any kind of check valve on the water supply line?

Um, no. I want any excess pressure to push back against the house supply rather
than pop the pressure relief valve. Do you think that is a problem? (There IS a
check valve in the closed system to make sure it runs the right way. )