Thermosyphon with Sidearm HX

Hook the hot in the relief valve . Use a tee. You have a plastic part in the cold line that keep heat from syphoning and it also sends the water to the bottom. You want the hot going to the top of the tank and cold coming out the bottom. Also connect to the tee as close as you can to the top. It's hard to send hot water down.
leaddog

Also a good idea to put a coin vent at the top of your sidearm to release trapped air.

Rob

I am a fan of circulator, smallest one you can get [bronze or SS]. The other thing you don't hear much here is that it takes a long time to heat the DHW and the recovery time is slow. The boiler has to be hot to get heat transfer. get below 140 and it slows things down a bunch.
I have a 200 gallon preheat tank and a U-tube heat exchanger [very good stuff] My system also uses the DHW tank for the floor heat Via a built in HX in the DHW tank and it gives me two exchanges witch makes the situation worse but with 200 gals of preheated water circulation threw both tanks One would thing this was a done deal and I still find my water heater running at times.

I have a SS circulator on my sidearm. It is on the bottom. Initially I had it sucking cooler water from the bottom and throwing it into the hot outlet at the top. This kept clogging up my screens in the mixing valve every day or two. I don't know why because the "debris" it was clogging it with was aqua in color and grainy, and this is a brand new water heater. Anyways, the fix was to reverse the circulator so it was sucking the water from the hot outlet and putting it into the bottom drain. It's been working perfectly for a while now. I'm not worried about thermal layering in my water heater since the circulator is in place. With the circulator, I'm actually getting 100% on demand hot water from my sidearm exchanger and I can take a really hot shower for as long as I want until I have to load the OWB again. I even turned off my water heater elements.

The earlier suggestion of getting the tee as close to the top of the tank is the secret. I struggled with this problem only to find that when the piping is an inch or 2 max off the top the syphon will then work perfectly. 6 inches above or more will not work consistently.
Replumbing isn't fun but it will work great and won't need a circulator. Good Luck!