copper tubing?

[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
Mythbusters Water Heater Explosion

[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!