Hey spa folks! I'm an ex portable spa user who can't live without a spa - but I want to go fancy. I have a 130,000BTU/hr high efficiency water heater for the earth-sheltered, passive solar house I built for myself. I built a 10X20 section of roof at the perfect angle for this latitude in North Carolina USA (36 degrees N) in winter to augment my radiant floor house heating system. Turns out I don't need additional solar for the house BUT I want to use it to heat an in-ground spa 75' away. I ran two 1.5" Schedule 40 PVC from the heater room to the spa area before building the house - so that's in place.
I believe that by installing a relay in my heater/radiant floor manifold room that shuts off the house heat during times of spa heating, the high levels of thermal mass and insulation of my house will keep indoor temps constant enough to be of no concern. I want to place ALL the equipment besides the topside controller in the heater room 75' away.
Can anyone advise me where I can find good instructions for creating such a system - or can any of you do the design for me on a professional basis? Or act as consultant?

I think that this system is beyond the reach of most "portable" spa packs, because of the 75' distance. Hurlcon did a wireless system some time ago that provided a spa-side touchpad (just like a portable spa) but with an on-wall touchpad for your house too.

Hurlcon is an Aussie brand distributed by Astral Pool - http://www.astralpool.com

Check their online cataloge for more info.