Can someone please explain how this condensing boiler diagram works?

[JohnDS]

Ok I am purchasing a Burnham Alp080bw-2g02 through gas company and while its on its way i have been looking at the piping diagram for it. I have piped a few boilers before but not a condensing boiler. The way they show this boiler piped is confusing. If you look at pages 57(without water heater) and 58(with indirect water heater) it shows that the boiler has its own loop with its own circulator and connects to the heating zone loop that has its own circulator (section A). I dont know but this does not make sense to me. Wouldnt it being piped this way not work unless you have some sort of mixing valve at section "A". Or better yet, why not just pipe it like a regular boiler with one loop going through boiler and through heating zone with the need for only one circulaor pump instead of two????? Someone please explain the significance of piping it this way as opposed to like a normal boiler?

Here is the link below....pages 57 and 58. Thanks guys.
https://www.google.com/url?sa=t&rct...8NuUw6ztMiSQ1XOt1841rBA&bvm=bv.56146854,d.dmg

 

[Caduceus]

I'm not much of a boiler guy, but I did read some of the literature and on page 54 section VI it explains why not to pipe as a conventional boiler.
When looking at the diagram I'm not sure as to why you would need a mixing valve at section A. What would the mixing valve be mixing?
Like I said, I'm not much of a boiler guy, but maybe a re-read of the installation manual could clear things up for you.
John is usually our go-to guy on these issues.

 

[JohnDS]

I'm not much of a boiler guy, but I did read some of the literature and on page 54 section VI it explains why not to pipe as a conventional boiler.
When looking at the diagram I'm not sure as to why you would need a mixing valve at section A. What would the mixing valve be mixing?
Like I said, I'm not much of a boiler guy, but maybe a re-read of the installation manual could clear things up for you.
John is usually our go-to guy on these issues.

Hey i appreciate any input. I was suggesting that the mixing valve would mix the hot boiler loop water with the zone loop water. The diagram seems to me that the zone loop will be recirculating cold water because what would make the zone water divert down the boiler loop to heat up when calling for heat? I am not saying this wont work as im sure its figured out and there is good reason, but im rather trying to get a better understanding. I will reread the pages you had specified, thanks again.

 

[johnjh2o]

What there doing is mixing some of the hotter feed water with the colder return water as it returns to the boiler. This makes it easier for the boiler to recover from a cold start.

 

[JohnDS]

What there doing is mixing some of the hotter feed water with the colder return water as it returns to the boiler. This makes it easier for the boiler to recover from a cold start.

Thanks John. Still weird to me i guess. It looks like the flow is going against eachother as well. Well i guess they have it figured out. Anyway, if the boiler has 1" inlet and 1" outlet, what size should the pipe be that the boiler loop, the heating zones, and the indirect water heater tie into on page 58. Im assuming 1" as well. So the heating zones and the indirect would be 3/4 tying into the 1" header along with the 1" boiler loop, correct?