Home Made Solar Hot Tub Heater

[Super noob]

Hello all

Has anyone made there own solar water heater?

My budget is $ 4 hundie so im thinking of using a salvage solar panel a solar water pump and a simple controller to shut the pump off at 105 deg F. If anyone has tryyed anything like this send me a message

Thanks

noob

[Guzz]

Hello all

Has anyone made there own solar water heater?

My budget is $ 4 hundie so im thinking of using a salvage solar panel a solar water pump and a simple controller to shut the pump off at 105 deg F. If anyone has tryyed anything like this send me a message

Thanks

noob

Yes, it has been tried, it's called the DAIT sytem.

[Dr. Spa]

Done it........ a few times. The solar panel will need to be a boxed glazed panel, and it's HIGHLY unlikely one 4x8 panel will do the job. I've got 3, 4x7 panels on my 350 gallon hot tub.

[sharkman009]

Done it........ a few times. The solar panel will need to be a boxed glazed panel, and it's HIGHLY unlikely one 4x8 panel will do the job. I've got 3, 4x7 panels on my 350 gallon hot tub.

How ell does that do in the winter?

[craighaggart]

If you know how much water your spa holds and approximately how much the water temperature drops in a typical day, you can easily calculate how much energy is required to heat it to a given temperature. Then, if you have some idea of the output of a particular solar collector, you can figure out whether or not it will do the job.

Multiply the number of gallons in your spa by the number of degrees (Fahrenheit) that you want to raise the water temperature. Multiply the result by 8.346, and voila - the energy in BTU. (If you do the same math but use 2.445 as the multiplier instead of 8.346, you have it in kilowatt-hours.)

For example, let's say you have a 400-gallon spa. You like the water at 105 degrees. You find that it drops to about 101 in a 24-hour period, so you need to generate enough energy to raise the temperature of 400 gallons of water by 4 degrees. This comes to a bit over 13,300 BTU (3.9 kWh), which should be well within the capabilities of a modest solar collector in a reasonably sunny area.

Remember, this only tells you the energy needed to heat the water, not the total energy needed to run the spa (pumps, controls, lights, etc.).

-Craig Haggart

Sunnyvale, California

[Chas]

For example, let's say you have a 400-gallon spa. You like the water at 105 degrees. You find that it drops to about 101 in a 24-hour period, so you need to generate enough energy to raise the temperature of 400 gallons of water by 4 degrees. This comes to a bit over 13,300 BTU (3.9 kWh), which should be well within the capabilities of a modest solar collector in a reasonably sunny area.

Remember, this only tells you the energy needed to heat the water, not the total energy needed to run the spa (pumps, controls, lights, etc.).

-Craig Haggart

Sunnyvale, California

Continuing with your math would mean that this tub will only heat four degrees every 24 hours - so you will have to wait many days to use it after a refill.

Solar can be used to run a tub - and please don't overlook what Doc said about using glazed panels - but I would think a backup heater of some type would be a must.

[Guzz]

Continuing with your math would mean that this tub will only heat four degrees every 24 hours - so you will have to wait many days to use it after a refill.

Solar can be used to run a tub - and please don't overlook what Doc said about using glazed panels - but I would think a backup heater of some type would be a must.

And hope the suns shinning, this would not work where I was born.

[craighaggart]

Continuing with your math would mean that this tub will only heat four degrees every 24 hours...

Maybe it's easier to think of it in kilowatt-hours instead of BTU. In the example, it took 3. 9 kWh to get the spa water from 101 to 105. If you had a heater that produced, say, 4 kilowatts of power, the water would go from 101 to 105 in one hour (4 kW times 1 hour = 4 kWh). Leaving the heater off for a day would result in water that was again down to 101 degrees.

If you reduced that heater's output to about 163 watts and left it on all the time, it's the same amount of energy as 4 kW for one hour per day. Since that's about the amount of energy lost by the spa in the example, the water would stay at about 105 all the time because you would be continuously replenishing the energy being lost.

But, as you noted, a solar collector does not work for 24 hours per day. It must be sized such that it produces enough power in a short enough time. And, unfortunately, solar collectors put out the least amount of power when you need it most: when there's little sunlight and a large temperature differential between the spa water and the surrounding air and ground. Therefore, if you want a solar collector to be the sole source for heating the water, you need one with sufficient power output to provide enough energy under the worst conditions. If you live in a cold climate and you have a big tub and you like it hot all the time, that means a very large collector and an additional storage tank to draw hot water from after the sun goes down.

-Craig Haggart

Sunnyvale, California