solar heating a hot tubby Admin
Oct 2012


i have a large solar thermal system that heats my water heater and a mass sand system under my house.  when installed we put valves to potentially heat a hot tub.  could this be adapted to heat your hot tubs, and extimate cost for medium (6 person) hot tub.  thanks



Dated on : 20-10-2011



Replies :


It could, but it isn't all that simple.  Your main energy storage is the sand under the house, and it probably does not get all that hot, to be useable heat source for the hot tub.  The tank on the other hand , would have hot enough water, but it may not have enough storage capacity to cover the hot water needs and the hot tub needs.  Or it may not have a top heat exchanger coil.

Next the hot tub controller determines when heat is to be transferred to the hot tub.  This request for heat must be interlocked with the solar controller so that the transfer will only occur when the water is hot enough.  This "hot enough" would be above the minimum temperature that is still adequate for the domestic hot water needs.

We ourselves, when we use solar to augment either the normal electric or  gas heating for a hot tub, modify the hot tub controller with two relays and then wire theses relays to achieve the interlocking.  The hot tub plumbing has a small pool heat exchanger added and a circulation pump is further added to pump water or glycol between the tanks top heat exchanger coil and the pool heat Exchanger.  The hot tub controller modification , the pump and the addition of the pool heat exchanger adds about $700 to the normal hot tub cost. With complete pump station and expansion tank its more.   You are responsible for the plumbing.

The cost of a normal hot tub you can determine by going to the following link.

You will get some idea of the system I am talking about by referring to the flow diagram attached.

Dieter Jung

Post By : Dieter Jung Dated On : 04-06-2011

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