sidearm question

[gradwell]

Finally have my project moving. House is framed, polebarn will be done tomorrow. Ran 5500 ft of radiant pex and waiting for Econoburn to be delivered. Question is, I havent yet decided if I will run my 2 Hot water tanks in series or reverse return, but I was wondering if I would need to run 1 sidearm since they will be connected or if I should have 1 sidearm for each unit. What do ya think?

Joe

 

[Eric Johnson]

Sidearms can either work by gravity or with the benefit of a pump. With gravity they take awhile to recover, but given enough time (overnight, for example) they can heat as much water as you can store. So you can probably get away with one, but you might want to pump the water through it instead of relying on gravity if you have a big demand for hot water. You might also need the pump to get the water into both tanks, although I'd have to noodle that one out. Gravity might take care of both. In any event, I'd consider using a larger shell (1.5 or 2" pipe) for greater capacity.

 

[gradwell]

how about 2 sidearm's, 1 shell? would that be possible? how large would the shell have to be?

Does it matter if the supply(from boiler) for the sidearm is on top or bottom?

 

[Eric Johnson]

If you can find or make a shell that can accommodate two 3/4-inch tubes, then it would work pretty well for two separate tanks (i.e., one tube per tank). Not sure how you would do that, but you can probably figure something out. The shell on my current sidearm is about 4 feet long and 1.5" in diameter (copper). My old one was about the same length and 1.25" diameter copper. Both have 3/4-inch tubes. As to the direction of flow, you need to pump the supply water from the top down in order to maximize efficiency with counterflow, since the water in the inner tube will be rising as it heats. I've piped it the other way and it works, but top-down is best. BTW, given the high cost of copper these days, especially the larger diameters, I don't see why you couldn't use black iron for the outer shell. Stick with copper for the guts, however.

 

[gradwell]

Thank you, sounds good. I had seen a post on this topic from somebody else that said they soldered a piece of copper wire I assume in a spiral around the 3/4 before inserting it into the shell to create turbulence. Have you tried this? Would this offer a notable difference?

 

[Eric Johnson]

I've seen sidearm tubes twisted (like ornamental wrought iron railings) to create turbulence and presumably greater surface area, but I just built mine with regular copper tubing. Works fine. I suspect that anything you attach to the tube adds to the surface area and makes it more efficient at transferring the heat. Since you're pumping the water through that side of the unit anyway, I think the more the merrier, since you don't have worry about disturbing the convection, which is all taking place inside the smooth side of the pipe.