Hoffman differential loop

DVW70

Hi. Was asked to weigh in an old vapor steam system - original 1929 national radiator coal steam boiler. Beautiful installation. Except running at 3psi…we’ll fix that. 

926 sq EDR, un-insulated mains (they are used to heat the basement.

Both returns are below grade assume meet at the boiler as only one return rises in the Mech room. 

original Hoffman Differential #1 still protecting differential. 

Question about new boiler……

Can I drain the old boiler and watch the water line to calculate the volume of water between operating and a half inch or so above low water cutout? 

Then that’s the available water for steaming and since the existing system works well, if I can match that volume of water in new boiler, shouldn’t this work out? 

The new boiler will likely steam much faster since it’s way less metal, and way less water, but the steam should condense as quickly as produced and head back to the boiler. 

It’s been a while since I’ve had to think like steam…

else I replace the traps and install F&T at the main ends, and install a boiler feed pump. 

Thank you for your input. David Van Wickler

KC_Jones

Just want to be clear on your question.  Are you suggesting sizing the boiler based on water content instead of matching system EDR?

You already know the current boiler is oversized if it’s capable of reaching 3 PSI, so why reference anything off of that?

DVW70

The existing radiation was calculated. The old boiler is oversized, but who knows if a new boiler has enough water to get condensate back before the burner goes off on low water?

mattmia2

Be careful of where the water line of the old boiler is and where the water line of the new boiler will be and that you dont make anything that needs to be below the water line above the water line like where drips connect together in a wet return. There are numerous ways to fix this, you need to consider the whole system in what is the right fix.

KC_Jones

To fill that entire system with steam would take around 4 gallons of water based on the posted EDR with some cushion. The boiler size you are talking about will have a water content at least 16 gallons, most likely more depending on brand and model. Now in order for what I just described to happen, you'd have to fill the entire system with steam before any condensate came back, which isn't going to happen, if it does you have a system problem, not a boiler problem. Even if it did, you'd still have a solid 12 gallons of water in that boiler, I don't really see an issue here.

If you had water content concerns, the solution would be to add a reservoir pipe. See page 19 of the Weil Mclain manual for an explanation of this.

https://www.weil-mclain.com/sites/default/files/field-file/EG PEG Series 6 Boiler Manual - Web Version.pdf

DVW70

much thanks for the help.

neilc

I would be more worried about the subslab returns,
and replacing them above slab where you can keep an eye on them and service them.

are they leaking water?