Help with DIY Pool Heater Idea

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Old 05-18-18, 07:32 AM
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Help with DIY Pool Heater Idea

First I apologize if I've posted this in the wrong place.

I have a small inflatable 1,500 gallon pool that I'd like to make a DIY propane heater for. I've read about this idea a few places and finally picked up a free gas grill to try it out on.

This is the general concept. Run some pool water through a manifold like this with the grill cover closed and propane gas running. Not something I'd run all the time as Id assume it uses alot of propane to raise the temp.

I'm not a professional, just a home DIY'er looking for a fun project. I've read posts online about heat exchange. Not looking to build the perfect, most efficient model but want it to work (raise the pool a few degrees so my wife gets in) and be safe.

Thoughts?
 
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Old 05-18-18, 08:04 AM
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My father built something similar for our pool when I was a child except it was wood fired and used steel piping. It worked quite well.


First some words on safety.

There is a reason all steam showers, water heaters and boilers have temperature and pressure safety relief valves. Steam explosions are extremely dangerous.

Do NOT install valves on the lines running to/from the heat coil. It could be extremely dangerous if the grill were operated with the valves closed so it's safer to not have valves.

Be careful with the amount of coils, the amount of heat you put to them and how much water flows through the heat exchanger. You MUST keep enough water flowing through the heat exchanger so the water can NEVER boil or turn to steam. It is possible to put in enough heat that it generates steam and the pipe with all it's restriction can not let the steam escape fast enough causing the pipe to burst or explode.

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If using copper piping with sweated fittings like your photo keep in mind that a propane grill gets hot enough to melt solder. So don't operate it without water completely filling all the pipes or your contraption might come apart.

The filtration pump that comes with most/all cheap inflatable pools is junk. They are barely capable of pushing water through the filter so you'll may need a separate pump for your heater. High flow rate isn't critical but you will want something that can generate moderate pressure to force the water through the restriction/resistance of all the piping and bends.

The easiest way to warm the pool is run a hose from the hot water spigot for a clothes washer and simply put hot water into the pool. Another cheap/easy method is to get a turkey fryer. Fill the pot with water and when it's hot... dump it in the pool.
 
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Old 05-18-18, 08:05 AM
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Well, you'll certainly get plenty of practice in sweating copper connections.
 
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Old 05-18-18, 08:20 AM
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Yikes, that's a lot of copper (I can do copper fittings, have done them for years, but I don't like it because somehow the job isn't done until I get bit by that one drip of solder ...)

The best DIY pool heater I've found is a sump pump pushing water through an 2" fire hose nozzle on the fogger setting- the fire hose nozzle cost $18. I'm also in Pennsylvania, found that the fogger nozzle produces droplets that are so small, they warm up to ambient temperature immediately.
So, on that one hot day in the week, use a sump pump to pull the coldest water from the bottom of the pool and shoot it up through a fogger nozzle. You can raise the water temp by about 15-20 degrees in one day. And the heat is basically free.


Other trick is to float a black poly tarp in the water- tie a few pool noodles to the edges to keep it floating, and secure it in place so it doesn't get pulled into a pool water intake, then re-direct the pool return hose so the cold return water flows across the black tarp.

Final trick, not sure if your pump or sump pump will work, but on a sunny day, I've used the fire hose nozzle and a 5hp pool pump to create the ultimate redneck solar water heater- pump shoots cold water from the bottom of the pool onto a hot garage roof, A rube-goldberg run of downspouts dumps the warmed water back into the pool. The heat is free, and it genuinely confounds the neighbors.
 

Last edited by Hal_S; 05-18-18 at 08:38 AM.
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Old 05-18-18, 09:35 AM
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That's what is often done for cooling. Even when it's a hundred degrees outside evaporation cools the water.
 
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Old 05-18-18, 01:29 PM
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thanks for this feedback Pilot Dane and Hal_S! Already re-thinking my plan...

Safety

First on safety, thanks. I had read that somewhere. I was going to do just that - control it with valves. So I will simply put on no valves at all, no harm in the water running through the system while the heat is off right? that way I'm safe and will always have alot of water going through.

Has me thinking about design though and making sure the water can get out.



Design

So speaking of valves, if I dont use any I wont be able to slow the flow through the system. I totally get your point about the pumps that come with these pools, so I already have a super oversized sand filter with pump thats usually for larger above ground pools. Way oversized for this application. So my plan is to "Tee" it off from the main return. Was going to do it with a valve but I think I'll just let it happen naturally. So my question is:

For optimum heat exchange I think I was the water to move through the pipes as quickly as possible, right? Or is it as slowly as possible? Cant remember?

Also the picture here was more of an example, I think think I'd make quite that many pipes/turns. But I believe I want as much coverage as possible within the space. Saw another idea and was thinking of using flexible copper tubing and avoid all of the soldering. Good or bad idea?


Alternative Methods


- Hot water line: good idea, any maybe more efficient way of heating. BUt this way I'd have to drain some of the pool water and top it off with hot. Not sure I want to do that.

- Turkey fryer: I do have one actually but def dont want to be lifting and dumping hot water. Maybe I can automate it somehow? Sounds like it would be less efficient than the design I'm talking about here. The propane usage, that is.

- Fire Hose on Fogger setting: now this is cool! Had no idea about this. However, does the ambient outside air temp need to be hot/warm to make it work? Or just warmer than the pool water temp? I would def look into this. Wonder how high up the water has to go? would you lose some to evaporation or would it all fall back down into the pool?

- Black poly tarp float: prob wouldnt work b/c pool doesnt get alot of direct sunlight. I do, however, have a solar cover so maybe I could still try this out.

- Redneck solar heater: awesome! totally see this working but I dont have a roof like that nearby. I was thinking of doing an actual DIY solar heater on my house roof if this doesnt work out.

Ok will do a little research on the fire hose idea. In the meantime if anyone could give some feedback on the flow / design of the pipes or copper tubing that would be great!

thanks
 
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Old 05-18-18, 02:54 PM
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For optimum heat exchange I think I was the water to move through the pipes as quickly as possible, right? Or is it as slowly as possible? Cant remember?
Thermodynamics says the most efficient exchange is longer time, highest heat differential, aka "counter-current heat exchange" The problem with the winding-pipe-BBQ setup, aka "kylothian pipe setup" is that it works more efficiently, but slower water flow risks steam pockets forming and blowing the rig up.

- Fire Hose on Fogger setting: now this is cool! Had no idea about this. However, does the ambient outside air temp need to be hot/warm to make it work? Or just warmer than the pool water temp? I would def look into this. Wonder how high up the water has to go? would you lose some to evaporation or would it all fall back down into the pool?
You want warm air, and cool pool water. The bigger the difference in temperature, the better it works.
I've used it when the pool-air temperature difference was about 20 degress, e.g. air temp 80-90 and water temp 60-65. There might be some evaporational cooling effect, but usually when it's 80 degrees in PA is't also humid-muggy so there's no evaporative cooling (e.g. if you tried this in Phoenix AZ, the water would just evaporate away, and you'd actually cool the water)
 

Last edited by Hal_S; 05-18-18 at 03:24 PM.
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Old 05-18-18, 06:42 PM
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Ok I think I'm going to move forward using coiled / cooper tubing to avoid sharp bends and soldering. Probably go with 50' of very small diameter tubing to expose as much of the water to the surface area of the tube as possible. Say 1/4" tubing.


EDIT: would something like this work? Not sure if there's a certain spec that will hold up to the heat.
https://www.amazon.com/Copper-Soft-Type-Refrigeration-Tubing/dp/B00UO0RWFM
in parallel I also have to try out the fire hose thing as well. Get a separate submersible pump. Too cool not to try.

Will lost pics as I do the build!
 
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Old 05-19-18, 02:34 AM
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I have used coils of copper tubing for heat exchangers when brewing and 1/4" will have a surprisningly low flow rate even especially considering how much water you want to heat. I would go for 1/2" tubing.

1/4" tubing think the output of a kitchen RO filtration faucet or fridge water dispenser. 1/2" will get you a flow rate closer to a garden hose.
 
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Old 05-19-18, 06:53 AM
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Eh, you DO know they make 1-2 gallon per minute RV/camping hot water heaters?

They run off propane, you can get them used for about $50, at RV swap meets?
 
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Old 05-19-18, 07:08 AM
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How about a simple, cheap solar pool heater?

https://www.doheny.com/doheny-above-...heating-system

You probably got more into the copper than the entire solar heater would cost!
 
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Old 05-19-18, 12:26 PM
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Plus one on the solar - I'm pretty happy with the heat, and I just lay it on the ground.
 
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Old 05-19-18, 01:52 PM
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There ya go.... 100' of 1" or 1-1/4" black poly pipe for $30-35..
You can leave it in a bundle or pull out like a slinky and let the sun hit it.
Cheap, easy and very effective. A slow flow of water is fine.

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Old 05-19-18, 03:31 PM
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thanks all. Originally planned on the Solar heater but the way things are laid out I dont have an area with alot of direct sun access. I'd have to put it up on my roof which I decided I dont want to do. Esp since I have a feeling it wouldnt generate water as hot as propane. so right now no solar until I venture to my upper roof.

@Hal_S - had no idea about the RV heaters. Will have to look into them a bit

Pilot Dane - ok, dont want to have such a trickle its not worth it. Will go with the 1/2 or 5/8 inch coil.

Trying to come up with the right design. 50' of 3/4" might be too much to fit under the grill. Maybe 20'.
 
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Old 05-19-18, 03:45 PM
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Don't forget to keep us updated with your project... and please get a little nerdy with the data if you don't mind. I'd love to hear things like the temperature rise through your heater and how long it take you to raise the pool temp.
 
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Old 05-19-18, 03:58 PM
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You don't even need that- Black flexi pool pipe is even cheaper-
Lay it out in a zig-zag pattern, if you want to be all "engineer-high-efficiency" place it inside sections of vinyl gutter and face them southward so they are heated by the sun but can't be cooled by breezes and convection.

Best pool hack I know,
Install a "T" fitting and a pair of gate valves on your swimming pool return pipe.
You can now "tune" the amout of water that bypasses the pool return,
About 30' of hose and fire-hose nozzle are a great start.
Great for dousing cars/carwash, bonfires, neices and nephews and curious neighbors.

And if you can find a good long run of black bendy pipe, you have a simple solar heater.
I arranged mine to face south, set it inside sections of unused PVC gutter, to concentrate the heat and shield the pipe from air and convection.
 
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Old 05-20-18, 05:30 PM
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keeping a eye on this thread sounds like its going to get good :-) please post pics of the build and final install
 
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