" I just have not bothered with messing with flow control to optimize stratification."

Let's say you did. So you can only throttle to reduce GPM which would give you higher temps on water from DSH.........or you could not throttle and have more GPM at a lower temperature.......both delivering the same amount of BTU's.

•••• So you can only throttle to reduce GPM which would give you higher temps on water from DSH••••

And sometimes, that is all we want to do!

Bergys drawing is definitely a tested way to pipe the Desuperheater. It works well when done as he drew it. I think FBBPs drawing might be better, the benefits are marginal but still maybe worth it. My question for FBBP is How are you purging the coil with your set up? It doesn't appear that you have a way to direct full domestic pressure and flow through just the coil.

geodude - if your pump is below your coil, would you have to flush? You are not building a trap at the top, nor do you have uneven pressure.

You might need to use a spring check to prevent total gravity flow.

Those tiny pumps cannot move much air and it needs to move it through multiple circular passes. It should only need to be purged once. But yes. I think it is necessary.

•••Those tiny pumps cannot move much air and it needs to move it through multiple circular passes.•••
Fair enough. Lets put a boiler drain between the DSH and the throttle valve. Main service pressure to atmosphere should be able to move any air and might serve as a good flush mechanism if DSH produces any debris. (gives me an excuse for the throttle valve if it proof ineffective ;-) )

The thing is, when you pipe a DSH directly to the finishing tank, you will have a lot of debris from the two heat elements so you don't want to suck from the bottom.
You can't pipe to the top or you would conflict with the already finished water and you don't have the element holes available for alternate use.
For these reasons, you pipe a single just like the Bergy.

You all seem to agree that adding a DSH to a single tank is a waste of money but for some reason just move the same piping layout to the buffer tank. None of the reasons for piping a single apply to the buffer.

The buffer tank does not produce debris. The DSH produces way less if any debris because it is a gentler heat source and in a constant water flow. If it did, you would have to acidify it regularly.

There is no advantage to piping hot(ter) water to the bottom of a buffer tank when you want the hottest water at the top. There may be an advantage to circulating the top tank water through the DSH until it reaches a preset and then switch to drawing from the bottom.

Think of it like this. If the DSH produce three gallons of 140º water, would you rather dump this directly on your head as a shower or would you mix it with 37 gallons of cold water in a bath tub? While the three gallons of 140 is too hot for most of us, it is just right for the finishing tank. It doesn't have to add any power to use it. On the other hand if you mix it with 37 gallons of cold water in the buffer tank and then ship three gallons on the resultant to the finishing heater, the finishing heater will still consume a lot of power heating this water.

Most DHW is used at a few gallons at a time and then no use for a period of time. This gives the DSH time to reheat another two or three gallons. Piping hot to bottom means the finishing tank always has to add heat except maybe first thing in the morning when the DSH has had all night to totally heat the buffer. The only time you get to use all the btu's produce with the bottom loading arrangement is when you drain the whole buffer tank, say for the three and one half showers or if you fill a tub.

•••• So you can only throttle to reduce GPM which would give you higher temps on water from DSH••••

"And sometimes, that is all we want to do!"

So that's it then. We are going to go around in circles because you think higher temperature is better. Put a monitor on your system and prove it saves.
Meanwhile I will avoid voiding the warranty on my buffer tanks by not threading pipe nipples into what is intended to be a gasketed joint.

Also possible to do the dip tube mod I posted earlier if adverse to DSH return into one the element ports. Either method gives similar results. The idea is to return nearer to the center of the buffer with sideways velocity that is low enough to avoid complete tank mixing. But yes, modifying anything on an new expensive buffer tank is likely not prudent for warranty purposes.

I used my old electic heater tank, so modding a dip tube was not a warranty concern. I would think a lot of installs may use the old hot water heater as the buffer.

Without some data logging, cost savings are speculation, but, the theory makes sense and are well used in other fields. An increase in stratification may or may not result in less overall BTU's transferred to the buffer, but the upper part of the tank will be usually be hotter and that is good for typical hot water draws, which are short.