Solar Hot Tub Heater

not a bad idea… what are you using for your tank?

Thank you very much for sharing.
I also think it could be more efficient to allow the water to heat more time before pumping it in the tub.
I have hooked my solar boiler to a storage tank and pump the water each hour,
the max. temp. difference (solar boiler) is about 40 degrees Celcius.

The capacity of the solar boiler is 6 litres approx., the storage tank about 60.

Depending on the sun, at 15.00 O’Clock the temperature of the water in the storage tank reaches about 45-50 degrees Celcius.

I have a thick cover on the tub. I set the tub for 102 degrees, and on warm days the solar panel will get it up to 105-106, which is a tad warm. By morning it might be down to 104. I estimate about a degree a day of loss during the summer without anything connected to the tub. The solar panel keeps it up around 102-104 during the spring/summer/fall months with no electricity use.  This is a smaller tub (300 gallons). If you have a large tub, you might need two panels (400′ of tubing).

It’s been freezing at night lately, but barely. I’m not sure it would do well in a hard freeze, especially the pump. It does not drain down at night, but if you used a larger pump you could probably work out a drain down system. The small pump needs to stay primed all the time, and the siphon effect helps move the water.

I think I said in the video that I used 5/8″ tubing, but it really is 1/2 in tubing. 5/8″ would work fine, maybe even better for a large tub. I used a roll (from home depot). I think I used about 200′- it was only about $10 for the tubing.

Hmm I see, I thought the thermostat ran the pump and would hold water in the hose until it got hot then shut off when it got to cooler water thus cycling the pump. different flow rates resulted in only different cycle times. With your design working so well though, I am going to replicate your design as closely as possible. Thanks for the info.

My pump only pumps about 45gph. 500gph is probably overkill and will cause the water to flow too quickly through the tubing. If the water flows too quickly, it won’t heat up enough.

I’ve had this hooked up for the past couple months, and the electric heater on the hot tub has only kicked on a handful of times. In fact, I think I need add a high temp cut-off on the panel intake because the tub as actually getting too hot (104-106), and it isn’t even summer yet!

Update: It’s been in the 80s for the past few days and the tub has been running between 104-106, with no supplemental electric heat. I have the thermostat set at 101, so it never turns on. Even with temps in the 70′s, the tub stays around 102-103.