motor sizing for radiant floor heat

[aztom]

I've got a loop of 475' of 1/2" (375 and about another hundred through three flat panel collectors,in parallel). There's about 14 elbows in the loop.
How big of a motor and what type would get the glycol flowing fast enough to warm my concrete floor without being too big or heavy or expensive or noisy or power-consuming?
I know my little Watts 500-800 1/25 hp. will hardly move the glycol at all.
Should I be considering a 3 speed pump to help adjust the temp of the glycol.(i.e. not letting it boil, or be to cold to do any good)

[Buffalobillpatrick]

So if we round off to 500' of 1/2" pex

It would take 19' of head (8.1 psi) to move 1 gpm, and 65' of head (27.7 psi) to move 2 gpm. So there isn't much flow in your future.

If you put 2x Taco 008 pumps (fairly high head vs. energy used) in series (output of 1st goes into 2nd) they would pull about 1.68 Amps & move about 1.2 gpm