Solar Hot Tub Heating

[danster26]

I agree with wrightylaaad. You should paint the inside of the box with matt black paint, it will absorb the sun rays better. Also, copper is not the best choice since it has the same characteristics as aluminum. It does not absorb heat, it will dissipate it. You would be better with stainless or cast iron. I would be reluctant to use pex or pvc because I would be afraid of overheating it since you have no control over it, looking forward to hearing what your outcome was with pex pipe.

[cooasty]

The information on pex states it is good up to temperatures of 200 degrees and not intended for external use. I guess pex will not be a good choice for solar applications.

Any ideas for a low cost solution?

[danster26]

I am working on a small project right now to heat my shop (1200 sq ft) It involves heating with hot water and the only thing heating it will be a 250 radiant bulb. I will post something once its done. I've done preliminary test and the temperature inside my water coil chamber was getting as high as 275 F to 325 def Far. (very hot) The total energy use will be 250 Watts and 200 Watts from a small circulation pump.

[aranelinya]

@cooasty you could just use black water hose. I have black water hose with a lifetime warranty that I am using. Cost a bit more at the outset...but should I need to replace it, hopefully it will prove to be worth the investment. Also there is some hose produced specifically for use with really hot water--mostly used by commercial enterprises.

[aranelinya]

@cooasty P.S. industrial hose withstands hot water temperatures to 200 degrees Farenheit and 500 PSI. and can be found online at webstaurantstore . com

[DaveTheyCallme]

@danster26  . I too would have painted the entire inside of the box a high temp. flat black for maximized absorbsion . Im currently building an enclosed wooden box but using a 300' coil of 3/4" Pex-B rated at 200 f. at 100 psi wrapped in a single layer of h.d. tin foil to prevent the Suns UV light from destroying it . THe absorber plate will be a thick piece of sheetmetal painted hi temp. flat black as well as the inner wooden walls and outer walls as well. Stagnation is regulated.

[cooasty]

Update......Moving water in copper tubing will eventually cause pinhole leaks due to internal erosion.......It's best to use Pex tubing.

[elhigh]

@cooasty Operative word there: "eventually." That also applies to how moving water carves out caves, marches Niagara Falls upstream at the rate of about a mile per century, etc.

I've had copper plumbing in my house for the last 40 years and so far, (knock wood) it's going strong. Also have a constant hot water recirculator on copper lines at work, in place nine years and no failures yet.

Actually, some leaks in the cast iron unions. But you get my point.

[cooasty]

Very cool!

[Naddycat]

Very cool!

[wrightylaaad]

if you spray the inside of the box matt black , then it will absorb even more solar heat