Probably THE most misunderstood concept in hydronics. The location of the expansion tank and its relationship to circulators (or pumps if you prefer). You can put it ANYWHERE YOU WANT, so long as ALL pumps are pumping AWAY from THAT expansion tanks connection point. It used to be called the Point of No Pressure Change, but has since been upgraded to Point of No Mechanically Induced Pressure Change. Reason being as water expands, the pressure goes up, There's real eye opening video that Bill Armstrong put out years ago that demonstrates the critical need to understand this cncept. I will go find it and copy it back to your site. Technically speaking, if you had a 1/2" port on top of the LLH, you could pipe the expansion tank there, and it would work just fine. In fact, if you had no choice (lack of space) and HAD to put it near hte bottom of the LLH, if you had a dirt leg off the LLH, and a side branch for the expansion tank, it would work just fine. The velocity of water being expanded is so low that it wouldn't be able to carry dirt to the tanks diaphragm. But I do agree with not putting it directly below the LLH/dirt separator. You're asking for trouble from solder balls and copper shavings getting into the tank and destroying the tanks diaphragm. I saw Siggy earlier this month. He's doing some tours with Caleffi and just happened to be in Denver. Got me out of retirement to take in his excellent seminar.

Those Idronics books are always awesome!!

How many retirement duckets will THIS cost me? Nice set up tho compared to the ones I've used.