Welcome to our forum.
Thanks Lars. No, the tub will be outside, about 20 feet from the house. I have seen a stainless steel heat exchanger advertised on-line that is used for swimming pools and supoosedly hot tubs. You run hot water through it from your boiler and circ the water from the hot tub through and the heat is passed by the metal interface. It sounds do-able and lower heat cost, but I am thinking it would be too quirky. Probably makes much more sense to stick with the heating unit that comes with the tub rather than do soemthing oddball. I thought I 'd ask anyway, just in case someone has done this successfully.
Seems like it would be a better fit for a traditional redwood type hot tub instead of a spa.I can't imagine trying to stuff it in somebody else's equipment compartment.