Solar Hot Water question - How can I control the temp of my hot tub when using a solar hot water heater set up?

I am building a solar hot water system for my hot tub. It will be independently plumbed to keep the original heater and pumps intact and operational. My question is, how can I get the solar system to turn on only when the hot tub is cooler than a certain tempurature and have it turn off if the water being returned from the solar system is colder than the hot tub's current temp? Any ideas would be appreciated!

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Check out this video:

resol bs3 solar controller will solve your problem here and you can limit the temperature to what ever you want to and even by want of a 2 port motorised valve divert hot water elsewhere
Rainh2o8 years ago
Im going to do this as soon as I get through building the enclosure for my hot tub...I was going to tap into the heater circuit of the hot tub to start with and see if this works. I was going to let the hot tub determine the temp and use the heater circuit with a relay to turn on my pump for my solar collector if this makes any sense....
Walke2jd (author)  Rainh2o8 years ago
The reason I wasnt going to do this is because I want to set two different temps. I will have the Solar setup heat the tub above 100 degrees. If the sun isnt out and the solar setup is out of commission, I want the hot tub heater to kick in, so Ill set the hot tub heater at 99. That way I never have to get in to a cold hot tub and I dont have to have the electric heater kick in at the same time as the solar heater. To Lemonie - I think my heater has the potential to get the water too hot. Especially in the summer where I try to keep my hot tub around 98. To Steve - No heat exchanger; the water will be heated directly through the solar heater and then piped back into the tub. I was thinking of using a solar panel to run the pump, which would take care of keeping the unit off if its not sunny. Im going to have to look into pipe mounted thermostats, but I think I really need something that will turn the pump off and not just restrict flow to control temp. Thanks for the advice so far!
lemonie8 years ago
Do you anticipate the solar heater making the hot tub too hot?
How about a domestic central-heating thermostat or similar? (Think about how you'd plumb that into your setup)

L
Is there a heat exchanger somewhere ? Is the solar system electrically pumped ? All you need are a couple of pipe-mounted thermostats I think. Steve