Staged boiler retrofit design questions

fwmech

Hello all,

I have a job coming up for a church in a remote village in Alaska. The existing system was designed by one of Dan Holohan's "Dead Men", a mechanical engineer in 1993.

The overall job is the replacement of two oil fired Burnham V78s with two new oil fired Burnham EMP336s. It is not in the budget to do a full mechanical room overhaul, and the engineer's I consulted were also not affordable for the congregation, so I am going to have to work with what the Dead Man left me:

A return manifold of circulators pumping towards the pressure tanks and boilers. A Tekmar 252. The current boilers are not piped as primary/secondary and upon inspection, the tekmar was never actually wired to the boilers. The low voltage wires were run to the boiler's controls, just not actually landed.

From my self-education using Dan's books and Siegenthaler's book, I am thinking that this should be a relatively simple enough installation to accomplish, as far as building a primary/secondary loop system goes. The new boilers will be flipped 180 degrees from the old ones, and as far as I can see, I should be able to run a design similar to the one on page 135 of Dan's book "Hydronic Radiant Heating" where each boiler is it's own individual secondary loop that can fire using the Tekmar to cold start when it's that boiler's turn.

My hang up is I am not understanding if I would still require a primary circulator or would the zone circulators accomplish that task? Also, being that the circs are pumping into the manifold, how would I pump away from a pressure tank, unless I built a circular race track with a primary circulator installed downstream of the PONPC?

Here are some pictures that I took and a hand sketch with sizes.

I would appreciate any knowledge or tales from those who have experienced similar design situations.

Thank you!

Mark

PXL_20250620_150216055 (1).jpg

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Mech room.jpg

EBEBRATT-Ed

Looks like they had pumps on the old boilers at one time as the flanges are still installed.

I attached a crude drawing

pipe.pdf

hot_rod

If you don’t need multiple temperatures or have high pressure drop boilers, parallel piping is fine, and they can still stage

hot_rod

hydro seps are more common for combining boilers

You get air, dirt, magnetic and hydraulic separation with one component

fwmech

https://forum.heatinghelp.com/discussion/comment/1867199#Comment_1867199

You're exactly right, they have what we called "knockout spools" in my big pipe days. It's pretty common in the bush from some well meaning handyman to do anything they can to get a boiler running based on their knowledge. Especially when it's -40!

By the way that's a very nice "crude" drawing!

fwmech

https://forum.heatinghelp.com/discussion/comment/1867207#Comment_1867207

I think a hydronic separator is just the ticket! Great suggestion, thank you @hot_rod !!

hot_rod

You have some flexibility with expansion tank placement when using a separator. Often it is right at the sep on either return.

Or at the end of the header, this works well with base mount expansion tanks for example.

fwmech

https://forum.heatinghelp.com/discussion/comment/1867223#Comment_1867223

Understood, thank you. The tanks are remote, piped up and over equipment via 1/2" Cu. I should have the ability to pipe that 1/2" line anywhere assuming that the connection is the PONPC?

EBEBRATT-Ed

I would not pipe with parallel flow only with that many zones and circulators. I know many say that a cast iron boiler does not care about flow. But I care about flow with any heat exchanger. I would use primary secondary of some design. I think any HX especially a direct fired one should have full flow through the boiler. JMHO

hot_rod

https://forum.heatinghelp.com/discussion/comment/1867229#Comment_1867229

correct, where you connect the expansion tank into a system, establishes the PONPC

Physically the tank can be remote mounted

fwmech

https://forum.heatinghelp.com/discussion/comment/1867250#Comment_1867250

Thank you for the suggestion. I will read up so I fully understand how to accomplish this.

hot_rod

the manual shows piping options and suggested flow rates

A hydro sep would assure adequate flow same as the bypass piping they show

You could confirm piping designs with Burnham tech support