Solar Heat for Spa

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S

SWFLNICK

0
Dec 7, 2011
40
Naples, FL
Hey Guys,

Had a question on heating our attached spa with solar.

I Finally got my pool crystal clear and we now are itching to use it. We currently have no heat source however since the previous owners of the house, or somebody (we just purchased a foreclosure) must have taken the heater as the wires/breaker box etc.. to hook one up are their, just no heater.

Anyways, I decided on going the Solar heat route for our pool, since during the summer it will heat is great plenty, and the winter months we won't worry much about using the pool, but will be using the spa mostly.

I will have 200 Sq Ft. of solar panels to heat my pool which has a surface area of aprox. 375 sq ft.

My question is how warm will it be able to get my spa during the day, if I am only recirculating the spa water through it? ( 6ft. diameter spa aprox 500 gallons)

I am just curious to see if it will be able to get it up to at least 95-100*F so it is at least nice and warm when sitting in it. The water temp with no heat source right now is around 69-70*

I guess I will find out after I have things up and running, and will post an update (I should be installing them up within the next 2 weeks) but am curious to know how warm I can expect solar to get that small amount of water, and if anyone else uses just solar to heat theirs, or has experience with it?

Thanks :cheers:
 
It kind of depends on the time of year. In the summer, I can get my spa over 102 degrees. But in winter on cold days with the wind blowing, forget it.

In your location during the winter, it should be possible on warm days to get a decent heat rise but it depends mainly on the air temp.
 
Thanks for the info. I do agree that time of year is going to play a big part. Average temps here during our entire winter is around 73-75*F during the day. We also have sunshine like 95% of our days during winter months so I wonder how warm it will be able to keep it during that time.

I have no doubts summer months will be able to keep it HOT, being average air temp is around 91-93*F from beginning of June to mid October and it only gets down in the upper 70s at night. Even the water temp at the beaches reaches 90* during the summer. I doubt I will have any desire to sit in a hot tub when it is already so hot and humid out, but that is when it is perfect for swimming in the pool!

So I guess I am mainly hoping during winter months to be able to get the water temp in the spa into the low 90s even, that way we can at least make some use of it.

How much of an increase do you see using the solar for your spa over the regular non heated temp? I know when using solar for a pool a 10* increase in temp is easy to achieve. So for a spa is it capable of reaching and increase of 20* or even more? If that is possible then I think I should be able to achieve above 90*

It would be awesome if the solar could do it, then I would have no need for a heater and can simply use solar for everything.
 
As shown in this post, if you use standard black mat unglazed solar panels, then with no wind you can't get more than about a 50ºF temperature rise even if your spa was perfectly insulated. In practice, it's usually difficult to get much more than 30-40ºF above air temperature (for my pool, the limit is more like 30ºF but I have a thin opaque cover instead of a bubble-type cover). If you have glazed panels (i.e. covered with glass like a greenhouse), then you can do much better which is why such panels are typically used for hot water applications. Given your relatively warm winter temperatures, I think your existing panel situation will work OK so long as the sun is out and you don't have wind.
 
I you want to get into something different Google "evacuated tube solar collector" I looked at this awhile ago, it's used for heating the home, domestic hotwater, pool/spa. They will give you hot water even in the dead of winter with chilly air and even with snow on them I've read
 
As I showed in the post comparing different technologies, an evacuated tube is not much better than a glazed panel (such as Gobi-style) in many conditions and as shown in this file the evacuated tube can be "too good" in the sense that it stays so cool that frost, ice or snow can stay on the tube preventing sunlight from getting into the tube. The Gobi-style glazed panels are about 3 times as expensive as flat mat plastic panels, but the evacuated tubes are about twice as expensive as the Gobi-style glazed panels. For domestic hot water or heating your spa, I suggest looking at the glazed panels such as those from Heliodyne and others. The best evacuated tube only starts outperforming Gobi-style glazed panels above an air/water temperature difference of 90ºF at 800 Watts/m2 or 36ºF at 300 Watts/m2 assuming they don't frost up.
 
Being within miles of you in Bonita Springs, on 12.15 the water temp was 72 and using our heat pump, we were able to raise it to 102 in one hour.

Just FYI should you decide to go the heat pump route.
 
Heat pumps are the way to go dollor/ operating wise vs gas. Now if they would just build comparable units to match gas like 200k to 400k and not charge 12g for them they would have something.
One of my friends has a pool spa that shares a 400k gas heater, he can raise the temp 1 deg per min! So in 12 short mins it's feeling good, in 20 mins is cookin! They use the hot tub a few times a month so it's perfect, no ongoing fuel cost to maintain a temp.
From what Ive read if you can afford the hardware the cheapest way to heat a hot tub that's used once a week or less is by this meathod with a high btu to spa capacity ratio.
I
obviously if it's sunny enough solar is free.
 
Heat pumps are the way to go dollor/ operating wise vs gas. Now if they would just build comparable units to match gas like 200k to 400k and not charge 12g for them they would have something.
One of my friends has a pool spa that shares a 400k gas heater, he can raise the temp 1 deg per min! So in 12 short mins it's feeling good, in 20 mins is cookin! They use the hot tub a few times a month so it's perfect, no ongoing fuel cost to maintain a temp.
From what Ive read if you can afford the hardware the cheapest way to heat a hot tub that's used once a week or less is by this meathod with a high btu to spa capacity ratio.
I
obviously if it's sunny enough solar is free.
 

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We want to do the same thing! Do you have an update on how well this worked to heat the spa? We would like to skip the propane heater to save money and energy. We are in the Austin, Texas area and have lots of sun, so I think our climates may be similar.

We are going to have a 7 ft square spa, next to the pool, completely in ground, with spill over into the pool when in recirculating mode. As I understand it, when we put it in spa mode it does not recirculate to the pool.

How hot can you get the spa?

What temperature do you like the spa to be when you're in it?

How long will it stay at that temperature without reheating?

Can you run the solar till the sun goes down to keep it at a certain temperature, then how many hours later can you still use it?
 
We have had great sucess with the solar heating the spa. I also have a solar cover on it too but on a day with sunshine im able to get it anywhere from 95-105which is too hot for me. I like it around 100. Recently got a solar cover for our pool too and now with the panels even during winter im able to get my pool in the mid 80s most days. Solar is just awesome and the best money I could have ever spent on our pool.
 
That's encouraging! Also, thanks for posting your info on cost - much cheaper than a company we've been talking too. Maybe we should look further before we pay full price instead of doing it ourselves. Although the solar company claims that we could get an isolated spa up to 120 degrees with their panels (from my reading on this site I would say they are the unglazed type, they look like black plastic).

I would rather not heat the spa up to an unsafe temperature. (Not sure exactly what temperature is unsafe either, but 120 sounds hot!) When you heat it to 95-105 during the day how long will it stay at 95-100 into the evening?
 
Ive had ours to 110 and could have got higher but it was way too hot to use. Public spas cant ben over 105* I believe so thats as hot as you will need it ever. With the cover on it will hold the temp for a few hours. It might drop a couple degrees but not much. Once you take the cover off and get in tho with the water recurculating depending on temp outside you will get about 1/2 hour to hour of use before its cooled down that its not nice anymore. Thats the only thing when using solar..if u use the spa at night the temp will drop because you have no heat source..we've found that it stays warm enough plenty long for our use tho.
 
That's exactly what we were wondering. You can do all the calculations but not knowing how much heat the walls, etc. absorb nothing beats real experiences.

From your information on do-it-yourself pricing I've been looking around and I would say that the amount of time you get out of the spa sounds like it was definitely worth it at your price, but wouldn't be worth it at $5000 the solar company I have a quote from would charge us. :) Thank you!
 
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