Well, he is going to pour this week or rather pump so not sure if I can do
all of this or not. Can one use PVC for warm - not hot- water for heating
the floor?

Probably not a good idea - PEX (crosslinked polyethlyene) is made for
the job, and pretty commonly available.

PEX is pretty cheap and can be gotten at nearly any major hardware
store now. 1/2" should run you about $.20/ft. For a shop you can go
pretty wide at about 15" centers on the loops. Figure ~ 1' for 1sq ft
and you will come out pretty close.

If you have big doors(garage doors, etc) or areas where you know you
will have higher heat loss, put a higher concentration(8-10") there and
if possible try to make them the hot end of the loop.

Each circuit should be no more than 250' for a practical limit. 300'
is a max without having to go to a high pressure pump. If you need
multiple loops, try to keep them similar lengths. It will avoid having
to add balancing valves and other stuff.

Do a google on radiant heat and design and you will find plenty of good
info.

I have a 80gal water heater that I rewired to use both elements
simultaneously. My electric bill goes up about $50 in the winter.
This is Minnesota winter, so it's a pretty good load. An electric
boiler would be smaller. Debatably more efficient.

FYI: Figure it will take 2 days to do everything. One day to prep the
base and lay down all of the foam and make sure it's all correct. 1
day to layout the lines. Depends on the crew, but it's not hard to do
just time consuming. If you have a drawn out plan and make marks on
the foam and then have someone put in clips it's easy to follow back
again with the PEX line.

I definitely will do the smooth finish, I am not sure that I can do the
heated floor and besides, what do you heat it with or, how do you heat the
water?
It's up to you, but for $2-300 to have the easy option to add heated
floor, would be worth it to me. Heated floor is REALLY nice, and you
are going to have to add some sort of heat eventually.


Depending one the heat load, a hot water heater, or a hot water furnace.
Some contribution from solar panels is also a possibility.