Quote Originally Posted by PoolDoc View Post
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.