Sidearm heat exchanger questions

[warno]

Since I've got my boiler up and running in the garage I'm already thinking about next year's plans of plumbing the house to it as well. My first order of business is building my side arm for my DHW. I have more then enough provisions to build a nice sidearm but I have some questions first.

I'm going to use a stainless steel outer sleeve and either stainless or copper inner tubes. The stainless inner tubes would be easier for me to build but the copper will transfer heat better. My question is what solder/flux do I use to hold the copper tubes to the stainless? I know it will have to be potable water safe solder and that's what makes me a little nervous if I use the wrong stuff. I'm assuming 100% silver? Also The smallest copper tubes I have available to me is only have 5/8" though.

I was thinking if I went with stainless inner tubes I have 3/16" through 5/8" stainless tubes available to me. I could use a bunch of smaller tubes to increase suface area and just TIG weld everything together which like I said would be easier for me.

What way would be better? Copper inner tubing or alot of stainless inner tubes? If copper, what solder/flux should be used?

Thanks for any and all advice.

 

[maple1]

Since I've got my boiler up and running in the garage I'm already thinking about next year's plans of plumbing the house to it as well. My first order of business is building my side arm for my DHW. I have more then enough provisions to build a nice sidearm but I have some questions first.

I'm going to use a stainless steel outer sleeve and either stainless or copper inner tubes. The stainless inner tubes would be easier for me to build but the copper will transfer heat better. My question is what solder/flux do I use to hold the copper tubes to the stainless? I know it will have to be potable water safe solder and that's what makes me a little nervous if I use the wrong stuff. I'm assuming 100% silver? Also The smallest copper tubes I have available to me is only have 5/8" though.

I was thinking if I went with stainless inner tubes I have 3/16" through 5/8" stainless tubes available to me. I could use a bunch of smaller tubes to increase suface area and just TIG weld everything together which like I said would be easier for me.

What way would be better? Copper inner tubing or alot of stainless inner tubes? If copper, what solder/flux should be used?

Thanks for any and all advice.

I think I would just go stainless & not look back. Looks like you definitely have the skills to do it. Would just have to make sure the welds get done good - since there will be DHW on one side of it, it'll see pressure of whatever your DHW pressure is. As opposed to the open boiler that has next to none. I think the place I got mine from had stainless ones also.

How much better does copper transfer the heat? I can't see it would be enough to be much of a hindrance.

 

[warno]

That was basically the answer I was looking for. The pressure vessels we build at work are tested at 350 PSI so I'll just use our air at work to test for leaks.

So the next question is how big to make it? Obviously bigger will recover heat faster but there's a point of too much overkill. It's only my wife, my little son, and I in the home, plus washing machine and dish washer. Then the obvious usage on the faucet through the day. How big are most sidearms?

 

[rowerwet]

I built my own from copper pipe. I read that most side arm HX's fail at the end welds due to the center pipe and outer pipe shrinking and expanding at different rates. I bent the inner pipe so it could flex like a spring when the delta was high. It never leaked.

 

[warno]

What exactly do you mean you bent the inner pipe? I'd like to only build this thing once.

 

[rowerwet]

Induced a slight bend to the inner pipe, not enough to touch the outer pipe when dry fit, but a noticeable bend.

 

[warno]

OK, that makes at sense. How big did you make your sidearm?

 

[rowerwet]

Six feet long, but for a normal install, don't make it taller than the height from the drain to a t on the top of your water heater.