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Continuously heating a pool can be expensive and the best ways to lower the cost are to have a cumbersome pool cover in addition to the equipment needed (solar or an AC-like heat pump). There must be a way to say, raise the temp of my pool 5-10 degrees using propane and a well crafted "heat exchanger". We don't go in the pool every day so if it cools off and we need to reheat we'll know the cost to do that is a tank of propane or so.

Does a propane heat exchanger exist? Can I make one myself? Can I use the same pump or should I set up a separate one just for heating?

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Pool covers cumbersome? I guess if your pool is an odd shape? Ours is rectangular and covering it is a breeze. Maybe we're just boring rectangular people? :-/ –  Andrew Heath Mar 17 '11 at 5:34
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Unrelated thought - would painting the pool sides and bottom black affect the water temperature? (ignoring of course how hard it would now be to clean!) –  Andrew Heath Mar 17 '11 at 5:35
    
Well, mine is rectangular too but the yard is small and the 18 inches or so of cool deck around the pool is the only way to go from one side of the house to another so I'd have to remove the pool cover just to move my mower from one side of the house to another. –  tooshel Mar 18 '11 at 20:46
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7 Answers

up vote 3 down vote accepted

Very late in answering here, but solar pool heating systems are great and pay themselves off in 1-1.5 years vs. propane and electric heaters. They are -- by a large margin -- the most cost-efficient renewable energy application that I know of.

Edit: After reading your question again, I see that you said solar pool heating requires a pool cover. It does not. A pool cover helps greatly, especially in a cold or dry climate: almost all of the heat a pool loses is from evaporation. However, it isn't really needed for solar. Is an uncovered solar-heated pool going to be 95 degrees Fahrenheit pool in the Winter? No, but it is going to give you 8-20 (depending on the size of the array) degrees Fahrenheit for free, which would costs thousands each year if done with propane.

Also, solar pool heating and propane are not mutually exclusive. You can easily get a system that uses both, heating the pool at all times with solar (provided that the panels are hot enough -- properly installed solar pool-heating systems bypass the solar if the panels are cold,) but if that isn't adequate, you can turn the propane on. As stated earlier, this setup saves thousands a year vs. propane. The solar portion of the system will pay itself off in ~1 year vs. propane, and it will save you $10,000-$60,000 over the life of the panels.

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Late but a good answer. I want to do solar but a friend of mine said it wasn't worth it on his pool (though, maybe he just didn't run it right). There is some cost involved to run it since you have to pump the water though the array. Only thing I don't like is I don't know if I want that kind of weight on my roof! –  tooshel May 18 '11 at 4:04
    
You just have to change the time at which the pool pump runs to 10AM-4PM or something like that. Since you're probably already running your pool pump for that long, it could very well be the case that it will cost you nothing to make hot water. Regarding the appearance of solar, pool heating is not typically installed on the front of a house. It's very true that solar can look like crap, but if you get someone who knows what they're doing, I think it actually looks good. This is one of my installations: solarcoordinates.com/wp/wp-content/uploads/2011/01/… –  Michael May 18 '11 at 4:41
    
Note: Solar pool-heating takes up more space than a domestic solar water heating system, so don't expect anything that small. Solar pool-heating takes 200-600 sq ft (you get about 4 degrees Fahrenheit per 20% of the pool's surface area in a decent solar climate,) whereas solar domestic water heating takes 50-100 sq ft. You don't live in my area, but nonetheless, I would recommend reading the web page I made that is dedicated to solar pool-heating: solarcoordinates.com/how_thermal_pool.html –  Michael May 18 '11 at 4:43
    
@tooshel Sorry I didn't address this earlier, but solar doesn't weigh much. Each collector should only have 0.5-2 gallons in it at any given time, so that's 4-17 lbs extra, and panels for pools should only weigh about 50 lbs. Spread out over a large area, it doesn't really add up to much increase in lbs/sqft. It should only come out to 2-3 PSF. Regarding your comment that your friend was not satisfied with his system, he must have gotten an improperly designed system that uses the wrong components. Evacuated tubes and other collectors SHOULD NOT be used to heat pools. (...) –  Michael May 19 '11 at 15:52
    
(cont.) Solar is very much a "buyer beware" market. Most "solar professionals" don't care about the performance of their system (i.e. the performance of their systems won't match their sales pitch) or are intentionally installing inferior products because they are easier to install or allow them to make more profit. Unfortunately DIY solar is even worse. Best bet would be to do your research to figure out what works and what doesn't (my web site has tons of info) and only purchase from someone that is installing a quality product. –  Michael May 19 '11 at 15:55
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When I was a kid, my much older brother heated the pool in his backyard by running a bunch of black painted pvc pipe to and fro on the fence, and then plumbed it into the filter system.

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simple and elegant, plus cost effective. –  allindal Mar 17 '11 at 4:11
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Can't beat this for the cost, but it depends on good sun. If you have a string of cloudy days, you won't get much heat. –  AWMoore Mar 17 '11 at 11:24
    
@AWMoore : Even on cloudy days, you still get a fair amount of sun; you could improve the heating by using some aluminumflashing or similar to make reflectors to direct more sun into the tubes, if you wanted. –  Joe Mar 18 '11 at 3:04
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You could cool your attic and heat your pool with one device:

http://www.solarattic.com/PCS2docs/graphic.html

Costs about $5k installed.

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How efficient is this really? I don't know much about thermal dynamics, but this thing is a heat pump that uses the pool water instead of refrigerants. Seems like it would waste a lot of energy moving water around, with less than optimal efficiency. Might be more efficient if it just placed a heat exchanger in the pool, and cycled refrigerants through the system as normal. –  Tester101 Mar 17 '11 at 12:14
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First time I ever heard anyone question water as a heat transfer fluid. Seems pretty popular in radiators. –  Philip Ngai Jan 7 '13 at 19:29
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If you definitely want to be able to use propane, or some artificial source, your best heat exchanger will be water, because it has such a high specific heat capacity, and in metal pipes, because metal conducts heat well. So essentially, you want a propane powered water boiler, with a set of pipes to circulate it through the pool. Of course the devil is in the details - how big should the boiler be, what burner and how hot, etc, etc.

For simplest setup, you could get a gas powered on-demand continuous water heater, then just run the pipes through the pool and back again. That takes care of all the details of boiler size, heat exchanger design, etc, but those continuous on-demand water heating systems are usually expensive. Hope this helps.

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I've always had an idea on how to more efficiently heat a pool:

For an in-ground pool made of concrete; attach radiant floor heating piping to the re-bar structure; connect this to a continous water heater and some sort of reservoir incase the water level gets to low and heat the pool from the inside out.

if laid out correctly, you could heat the pool from all sides - heat rises, transferring into the water.

I'm not a thermal engineer but I think it would work.

Could also use the water in the pool as the water that passes into the radiant floor piping and then dump the water back into the pool; not only would you heat the actual concrete and transfer into the water, but also heat the water going into the pool.

-Mario

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Quickly heating and cooling the concrete could cause cracks would be my guess. –  tooshel Mar 21 '11 at 20:12
    
Summary of your idea: heat water to heat concrete to heat pool water. How about just heating the pool water directly? –  Philip Ngai Jan 7 '13 at 19:30
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Is there something wrong a standard Propane Pool Heater?

http://search.intheswim.com/?q=propane%20pool%20heater

Some of the gas heaters linked above also have sizing guides and model info that can help you pick a heater large enough for your pool. Keep in mind that even with gas heat it usually takes 24h to warm the pool, so you don't turn on the heat and hop in.

For a pool that isn't used every day (or almost every day), an active heating system can be a waste of money.

If you don't use the pool all the time, I would consider something that is more "passive". Solar Heaters are pretty cheap, and the energy cost is basically zero. However, they don't provide a lot of heat (less so on a cloudy day), but it may be enough to enjoy the pool without shivering.

I'm not a fan of solar covers, unless you have a crank that allows you to easily cover/uncover the pool. The solar cover on our 27ft pool was so difficult to drag on and off (and keep it clean) that we gave up on it. We also ended up dragging a lot of crap into the pool.

Other options:

  • I had mixed results with a Solar Pill, but I also tried it late in the summer when the rains started.

  • Solar Rings look pretty cool. Might be easier to manage than the solar cover, and double as a pool toy. Expensive though.

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Answering a really old question... In the current season of Ask This Old House (aired during the 2012 Cambridge House TOH season), they used a heat exchanger to take waste heat from a heat pump (that the homeowner is already using to heat/cool his home) and use that to heat the pool. Something like on this site:

http://www.hotspotenergy.com/titanium-pool-heat-exchangers/

The output of the pool pump is plumbed to go through the heat exchanger.
The lineset serving the heat pump is spliced into the heat exchanger. There is a switch/controller that is part of the heat exchanger. When the heat pump runs, the controller detects if the pool needs to be heated (based on set temperature). If so, the refrigerant is routed through the heat exchanger, heating the water and getting dispersing the heat from inside the building. If the pool does not need to be heated, the refrigerant goes through heat pump as usual.

The heat exchanger was represented as using wasted heat (from inside the house) to heat the water, so the pool was heated for "free" without affecting the cooling of the house. Don't know if that is completely true or not, but that is what was said.

There is probably more to it, but that is what I remember from the Ask TOH show.

Note that in this segment of the show the homeowner already has a conventional heat pump that is used to heat/cool his home. The plumber/HVAC guy installed a heat exchanger that allows the transfer of the waste heat the heat pump generates during the cooling season into the pool water. This answer is not about having a dedicated heater for the pool. It is also not about heating the pool during the non-cooling season as the heat pump only generates waste heat when it is in cooling mode.

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Might be an old question but I'm still wondering. Most suggest to add what is essentially black tubing to my roof and that should "extend the season" but won't keep the pool warm in the winter. And it's not exactly "free" since you have to pay to pump the water up there and even with a variable speed pump it's probably the second or third biggest user of electricity for a homeowner. "People with experience" say that using gas to heat a pool, even for a weekend, costs nearly $100 even in a mild winter climate like in Phoenix, AZ. I've concluded we aren't swimming in winter! –  tooshel Jan 8 '13 at 16:28
    
In my answer, I was simply describing a product that I saw used on the television show Ask This Old House. The homeowner wanted to heat his pool during the summer (it was in a relatively northern latitude and was in a location where it did not get much sun). The proposed solution leverages the fact that the homeowner's existing heat pump (for heating/cooling his house) has extra "free" heat in the summer because that heat has been removed from the house. The "free" heat is transferred to the pool water via the heat exchanger. –  wageoghe Jan 8 '13 at 16:35
    
The heat exchanger solution seems like it would allow someone to heat their pool during the time of year that the heat pump is running to cool the house. So, the pool could be heated only during the spring (late?), summer, and fall (early?). Depending on how much you want to heat your pool, what time of year you want to heat it, and whether or not you already have a heat pump, this kind of solution might not be of much use to you. –  wageoghe Jan 8 '13 at 16:38
    
I live in a hot southern climate so that probably wouldn't work . . . although there is a bit of overlap where I'm cooling the house still and wish the pool were just a bit warmer. I'll run into that show eventually . . . I watch TOH and Ask TOH I'm just really behind! –  tooshel Jan 9 '13 at 17:26
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