Making a DHW coil?

[kuribo]

So I have a 4" threaded fitting welded to one of my propane tanks for installing an indirect water heating coil for DHW. Looking into them, they run a hefty $400 or so. So I am wondering if I might not make one myself as follows: use 50-60 feet of 5/8" soft copper tubing, bend it with say 4' lengths back and forth like a trombone. Solder some bulk head fittings on the ends. Drill two holes in a brass waste clean out plug (they have pipe threads I believe) and then screw this into my steel 4" threaded fitting. Screw the nuts and washers down on the bulk head fittings to finish. Alternatively, I could use copper fittings on the ends of the coil and solder them to the brass clean out plug.

I figure this should cost me maybe $100 or so....

Anyone see and issues with this?

 

[cityboy172]

I'm getting frustrated just thinking about trying to make all those tight bends you are talking about, And I'm a pipefitter by trade. Have you ever tried making bends like you are thinking about doing? If that was the way I needed to set things up, I would end up brazing at least half the joints more then likely. Good luck.

 

[kuribo]

I'm thinking there would be 8 or so 180 bends....I have bent copper tubing before....Worst case I buy 180 bends and solder them in....Still a lot cheaper than a $400 coil....

 

[jrod770]

This brings up a good question for my future build. What's better a sidearm heat exchanger on the water heater or having a coil submerged in the tank like Kuribo is suggesting? Just wondering of the benefits of one over another.

 

[woodsmaster]

This brings up a good question for my future build. What's better a sidearm heat exchanger on the water heater or having a coil submerged in the tank like Kuribo is suggesting? Just wondering of the benefits of one over another.

With a coil in the storage tank you don't have as much mixing of the storage water. Better stratification.

 

[maple1]

Flip side to a coil - is that if you use a bunch of hot water at once, it might not take long for that water to cool off unless you've got some flow across the coils going on in your tank water. Usually not an issue in heating season, but might be if you want to heat DHW from storage with it in the non-heating season.

 

[ewdudley]

Why trombone loops instead of round and round?

Speaking of round and round, deals show up on ebay and craiglist from time to time. I see you have a threaded fitting, but perhaps you could build an a adapter plate welded to a half-nipple and then be able to use the more common flange type mounting.

(broken link removed to http://hudsonvalley.craigslist.org/mat/4368036157.html)

(broken link removed to http://worcester.craigslist.org/mat/4348374096.html)

 

[kuribo]

I only plan to use it for DHW during the heating season. Summers I plan to use one the nyetherm HP water heaters with an 80 gallon tank.

Why trombone? Much easier to make than a coil. I have looked and looked for a 4" dia coil like those you have linked, but seems it is an odd ball size and I have been unsuccessful thus far. Maybe I will get lucky and find one for $100, otherwise, I think the trombone done in 50' of 3/4" copper should work well....I am wondering about the integrity of using bulkhead fittings, but seems that is what some of these tankless coil makers use so they should be ok....

Thanks for the replies....