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Harness the sun’s energy to heat your tub
Video Rating: 5 / 5
Tags: Heater, SOLAR
not a bad idea… what are you using for your tank?
it would work OK with an inflatable pool. You’d be better off with a bigger pool solar panel for a pool though. A pool needs a lot of water raised a few degrees, where as a hot tub needs a little water raised to a higher temp. This design circulates a little water slowly, thus raising the outlet temp to >104. A pool solar panel might raise water a degree or two at the outlet, which does fine for bring a large pool from 68 to 80deg, but no good for a hot tub.
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.
how important is the insilation on a hot tub? would something like this work with just any inflatible pool?
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).
How quickly does the temp in the tub drop at night? Its a great design but I’m trying to find something that keeps the tub/heater off the electric grid even at night
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.
Does it freeze where you live? Does the system drain down at night?
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.
great setup! I need to build one as I’m getting heat from my better half on the electric bill. how much tubing did you use? my speakers aren’t the greatest.
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.
You can still find the pump on Ebay. Search for “12V water pump P-38I”:
Rated voltage: 12V DC
Rated current: 0.57A
Capacity: 6.5L/Min (103GPH)
Pump head: 2M
Working temperature: -35C ~ +105C
Service life: 26000 hours up
Motor: DC brushless motor
Pump: Centrifugal pump
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!
Excellent design, I have been researching and this is the best I have come across. Do you know what the flow rate is on that pump? I am going to try it with a 500gph bilge pump I have.
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.
Like it man. Thanx for posting. Looks like your on to somethin’.
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