copper tubing?

[Charlie_R]

I don't know what the commercial heaters use in their heat exchangers, but I suspect it would be stainless steel.

Would there be a problem with using copper pipe in a home built solid fuel heater? If there are serious cons to this, I do have another method in mind, it just involves a lot more work, along with lower efficiency.

Would copper tubing require keeping a really close watch on pH? Would I be introducing copper ions into the pool? I've seen via the internet, many examples of people using copper in home built heaters, but with my lack of knowledge in this area, are they asking for green, copper laden pools?

Thanks for any info you can provide!

[Charlie_R]

I guess no one has any thoughts on this?

[PoolDoc]

You can use copper if you keep the pH between 7 and 8, and don't use salt.

The heat exchangers in commercial pool heaters are copper, just like they are in residential units. However, salt-compatible residential units have cupro-nickel exchangers -- stainless steel is a poor conductor and is not used.

NOTE: this is NOT a recommendation that you actually DO any of this. Building a heater is potentially life-threatening! It's surprisingly easy to build a water bomb -- when home water heaters explode they often level the house and kill everyone inside!

Here are 2 videos you should watch, before you go further:

50 Gallon water heater explosion (http://www.youtube.com/watch?v=l3i_ZGPtm68)
Mythbusters Water Heater Explosion (http://www.youtube.com/watch?v=9bU-I2ZiML0)

[Charlie_R]

Yes is would be dangerous if I used a closed container, without a temperature/pressure relief valve. Obviously, in both the videos, those key pieces of SAFETY equipment had been removed and the hole plugged.

If you have ever seen a properly equipped tank go into thermal runaway, the T/P valve lets loose well before an explosion can happen.

In this case, YES, I would plumb in a T/P valve. In addition, NO fire would be lit without water flowing through the heat exchanger, and would continue to run well after the fire was out. Under no circumstances would this be left unattended. There would be no pressure vessel (tank) involved in this build, if I do decide to go through with it.

[PoolDoc]

As I said, building a heater is potentially life threatening. You seem familiar with the safety devices typically used on water heating systems, so I presume you can experiment safely. But I didn't know that when I posted. There have been 3 or 4 prior posters this year with some other DIY pool heating system ideas and not one of them had a clue about safety.

When I post as I did above, I'm not only writing for you -- since you hadn't mentioned T&P valves, etc -- but also for all the lurkers who will Google "DIY pool heater", and end up here.

[Charlie_R]

I agree with your reasoning behind the reply, and I appreciate the reminder. I like the fact you care enough to post that kind of safety warning.

[PoolDoc]

Thanks for understanding!

[Charlie_R]

Well, I did it.

Took an old bbq grill for the housing/firebox, and bought 50' of 3/4" copper pipe along with a bunch of tees and els etc. Even with the fairly small firebox, I'm able to keep 80* water with overnight temps in the high 50s to low 60s, burning junk pallet wood.

I do need to make a few improvements to it, mostly to the flue gas path to bring more of the hot gasses in contact with the copper for longer time. I'm also going to have to enlarge the firebox a bit so I'm not having to add wood so often.

Took a swim this afternoon, 65* air temp, 82* water. felt good, as long as I was in the water, but getting out was problematic.....I got cold real quick!

[Charlie_R]

I goofed. Cost me 2/3 of the water in the pool.

Heater exterior was cool enough to hold my hand on. so I shut off the pump last night. Got up this morning to a muddy mess. One PVC joint failed, and broke free. I assume from residual heat in the firebox.

However, the up side to this is I was able to make the improvements to the heater.

Incoming fill water is measured 63*, yet the pool is holding at 72*, while filling. Current air temp 64*, high today was 68*.

I guess that means the changes to the heater are successful. Looks like I'll be able to get the water back to swimming temperature by tomorrow afternoon. Shooting for 80*+. Anything over that is just gravy......

[Charlie_R]

According to the typical internet meme, pics or it didn't happen, right?

With that said, here is what is happening:

Overall view of the system --

http://i1094.photobucket.com/albums/i459/bcgeorge/pool%20pics/th_P1010890.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/pool%20pics/?action=view&current=P1010890.jpg)

Yes, it looks hillbilly. That is what happens when you use what you have on hand. No filter in the canister, to keep the flow rate fairly decent.

Nice bed of coals --

http://i1094.photobucket.com/albums/i459/bcgeorge/pool%20pics/th_P1010891.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/pool%20pics/?action=view&current=P1010891.jpg)

This is what a pile of used, broken pallets are good for.

Detail of the suction/return lines --

http://i1094.photobucket.com/albums/i459/bcgeorge/pool%20pics/th_P1010892.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/pool%20pics/?action=view&current=P1010892.jpg)

http://i1094.photobucket.com/albums/i459/bcgeorge/pool%20pics/th_P1010893.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/pool%20pics/?action=view&current=P1010893.jpg)

And of course, I can't forget the thermometer --

http://i1094.photobucket.com/albums/i459/bcgeorge/pool%20pics/th_P1010896.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/pool%20pics/?action=view&current=P1010896.jpg)

According to http://www.wunderground.com/cgi-bin/findweather/getForecast?query=zmw:65265.1.99999 current air temp is 68*.

I must have done something right, this time!

[PoolDoc]

Uhm. Interesting?

Not sure what to say. It shouldn't be too dangerous, since if the copper overheats, the PVC will collapse before there's any sort of pressure build up. Plus, it doesn't look like you have any valves that would allow a pressure increase to occur.

Not sure how durable it all is, though. Any joints you have that are exposed to the fire are unlikely to last long, unless you used high temp silver solder. If you have calcium in your pool, and get build up in the coil, it can insulate the pipe from the water enough to allow the pipe to over heat. And . . . copper is not especially resistant to combustion gas effects.

But, time will tell.

[Charlie_R]

Uhm. Interesting?

Not sure what to say. It shouldn't be too dangerous, since if the copper overheats, the PVC will collapse before there's any sort of pressure build up. Plus, it doesn't look like you have any valves that would allow a pressure increase to occur.

I do have one valve on the return side, to be used only when removing the apparatus at pool closing. It remains fully open otherwise.



Not sure how durable it all is, though. Any joints you have that are exposed to the fire are unlikely to last long, unless you used high temp silver solder. If you have calcium in your pool, and get build up in the coil, it can insulate the pipe from the water enough to allow the pipe to over heat. And . . . copper is not especially resistant to combustion gas effects.

But, time will tell.

I really don't expect this to last more than 1 or 2 seasons in it's present configuration. This initial build is intended as a "proof of concept", to see how well it will work.

I used lead free potable water (95.6%Sn 4%Cu .4%Ag) solder on all copper joints. With water flowing through the pipes, I doubt that the joints will get anywhere near the melting point of the solder, even with a 10* rise in water temp from suction to return.

One other problem that I probably will need to address is the tendency of creosote to condense on the tubing. This was fully expected. Knowing that creosote is acidic, but not knowing how far down the scale it is, leads me to expect failure of the tubing itself within the 1-2 season life expectancy. At least this will give me enough time to procure thin wall stainless tubing, along with the means to either bend it or braze fittings into the shape I want.

I'm not sure I'll have much of a problem with calcium build up in the tubes, before the creosote corrodes the copper to the point of failure. Fill water has 180-240ppm calcium, depending on what week I check. I'm not sure why it tests differently one week to the next. Probably which well the water co drew from that week. For our domestic hot water, I've found that I need to clean our gas fired water heater only every 2nd year, so I think I can assume that the heat exchanger in the pool heater won't have too much of a problem with this before corrosion failure.

[PoolDoc]

For our domestic hot water, I've found that I need to clean our gas fired water heater only every 2nd year, so I think I can assume that the heat exchanger in the pool heater won't have too much of a problem with this before corrosion failure.

Not necessarily a correct assumption.

In your water heater, scale prevents heat from escaping as easily, but the scale stays wet (unless you hear popping noises) and so the heater element is temperature limited by the boiling point of water.

This may not work out as well with tubing exposed to uneven fire box heating, compared to tubing exposed to very even heat element heating.

BTW, you can prevent having to replace heater elements by using a low watt density Inconel sheathed element like this one:

Camco 4500W 240V Screw-in Water Heater Element -Ultra Low Watt Density (http://www.amazon.com/exec/obidos/ASIN/B0002YU2YS/poolbooks)
Camco 5500W 240V Screw-in Water Heater Element - Ultra Low Watt Density (http://www.amazon.com/exec/obidos/ASIN/B000BPG4LI/poolbooks)
Years ago, when I was a plumber doing commercial service work, these were hard to find. But thanks to Amazon, they are now available to everyone. In most installations, this is a life-of-the-heater replacement. Because of the much larger surface area, scale formation is greatly reduced. And, because of the inconel sheathing, the elements don't fail even when they do get coated with scale.

[Charlie_R]

Not necessarily a correct assumption.

In your water heater, scale prevents heat from escaping as easily, but the scale stays wet (unless you hear popping noises) and so the heater element is temperature limited by the boiling point of water.

This is true, and works the same in gas or electric water heaters. As stated above ours is a gas fired, and will remain so as long as gas is cheaper than electricity as applied to heating potable water, not to mention the differing inefficiencies of both.


This may not work out as well with tubing exposed to uneven fire box heating, compared to tubing exposed to very even heat element heating.

Yes, the uneven heating is a concern of mine. What I have done to reduce -- cannot eliminate -- this, is baffles to direct the hot gasses around the tubes to attempt to even out the heat each is subjected to.


BTW, you can prevent having to replace heater elements by using a low watt density Inconel sheathed element like this one:

Camco 4500W 240V Screw-in Water Heater Element -Ultra Low Watt Density (http://www.amazon.com/exec/obidos/ASIN/B0002YU2YS/poolbooks)
Camco 5500W 240V Screw-in Water Heater Element - Ultra Low Watt Density (http://www.amazon.com/exec/obidos/ASIN/B000BPG4LI/poolbooks)
Years ago, when I was a plumber doing commercial service work, these were hard to find. But thanks to Amazon, they are now available to everyone. In most installations, this is a life-of-the-heater replacement. Because of the much larger surface area, scale formation is greatly reduced. And, because of the inconel sheathing, the elements don't fail even when they do get coated with scale.

I have used these where former employers had rentals with electric tanks. I agree that they are worth the slight extra expense, at least in my area. In only one case did I ever see one of these fail, an upper element, and that was attributed to the tank losing water when the water supply to the house failed while it was unoccupied.

Would it be too much of a stretch to assume that the calcium scale would make it's presence known by a reduction of CH in the pool water? In my ignorance, I have the idea that the calcium in the water would have to precipitate out as it encountered the heat in the tubes, attaching itself to the source of that heat. I don't know that this is what happens in a water heater, but that is my suspicion. In so doing it should manifest itself with a change downward in the tested levels.