Rusted Hot Water Tank
We have an outdoor wood furnace. We had a sidearm for our hot water tank but we have gone through 4 tanks in less then 2 yrs. The hot water tanks keep rusting out.
We have had to disconnect our hot water tank from using it with the wood furnace which is unfortunate because that was a big selling feature for us.
Is there a solution? Answer
Your rusted hot water heater tank issue has me puzzled. From my experience, and after talking to several other people who use a sidearm heat exchanger, the sidearm should not cause your hot water tank to prematurely rust out.
A hot water tank should last around 6-15 years (or longer) before you have any issues with a leaking tank due to rust.
Plus, your hot water tank should have an anode rod inside of it that prevents the rust from destroying your tank. The anode rod is designed to deteriorate before the tank.
The anode rod is typically located on the top of your tank. It's a long rod that goes into the water and you should remove it and check it every once in a while to make sure it's still intact. Using a water softener can sometimes cause the anode rod to deteriorate faster.
Since a sidearm heat exchanger slowly moves your domestic water through the heat exchanger using a thermosiphon process, the slowly moving water should not cause your tank to rust out prematurely.
Here's my suggestion to solve your problem. Sometimes transient current can cause corrosion. It's a possibility that your outdoor wood furnace (or something else) is not grounded properly and small amounts of transient current are running through the sidearm heat exchanger. If this is the case, just make sure the incoming and outgoing pipes are grounded and it should solve your issue.
I hope this helps,
Firewood For Life