Primary circuit with condensing boiler?

NEkingdom

I am currently in the midst of a boiler replacement project in my 1860s 3,400 sf house in northern Vermont. My heating contractor is replacing a 30+ year old oil fired boiler with a propane Rinnai condensing unit, running 5 heating zones as well as an indirect DHW tank. The emitters are a mix of standard and high output baseboard units, with enough oversizing to allow running the units a little cooler than normal so hopefully I have some condensing operation going on in the shoulder seasons.
He hung the boiler late last week, and is returning in a few days to complete the installation once the new underground propane tank and gas piping is completed. I am trying to understand the circuit he is in the process of installing to make sure I am getting what I need to run an efficient and effective system.
He has installed some sort of a primary loop with its own circulator on the output of the Rinnai low loss header. The primary pump as well as all the zone pumps are TacoVR1816 units. The system control will be a Taco SR506 with priority for the DHW circuit.
I don’t get why he plumbed this primary loop, which I think of something done to protect non-condensing boilers from low return temperatures. Rinnai’s application guide doesn’t show any such circuit as this. I’m also not sure what control mode one would set for the primary VR1816 to run in this application. When I asked him about this setup, my contractor said it “made sure that hot water was instantly available to the zone pumps when there was a call for heat”. Does this make sense, or should I try to gently steer him (with his 40 years of experience) back to a more straightforward setup? I don’t want to be that troublesome customer with just a dangerous amount of knowledge (engineering background, and borrowed the Siegenthaler book), but this stuff is expensive and I want to make sure I am getting the job done right.
One other question, the Rinnai manual says a dirt trap is required when installing a new boiler into an existing heating system, but I don’t think my contractor has left provision to install one. I am assuming I should insist on the dirt trap, both for its function and to preserve any possible warranty claim down the road if I have a boiler issue?
Thanks in advance for any help and advice.

kcopp

That's not right.... The primary loop is the one that w/ the boiler. the secondary loop should just have the separate zones.

Paul S_3

Condensing boiler must have a dirt seperator.... preferably a magnetic dirt seperator like the Caleffi dirtmag in this photo....what type of heat emitters you have? Cast iron radiators?.....that pump is pointless there so is that loop....tell him to follow installation manual...also where is the expansion tank connection? Make sure the boiler is setup properly....if its not your efficiency will be no different than a standard boiler. If you have siggy's book....read about condensing boilers....keep the water temp as low as possible....what the btu output of that boiler?

Gordy

He does nice work I will say that. As been said the extra pump is wrong though.

I'm seeing 5 zone pumps, and 2 returns? Xtank?

Or leave that pump, and swap the zone pumps for zone valves.