Steam Change Out Sizing Question

offdutytech

Had a service call today to go over a 1933 US Boiler in their house they just moved into. Had been to the house before for an AC install and glanced at the boiler in the basement for the previous owner. 
Found a few issues with LWCO, main vent, pressure control and some radiator vents. Condensate pipe rotting out at boiler. Overall the system functioned better than expected. We wanted to give the customer a few options to repair or replace. I calculated the EDR from all the radiators using Dan's EDR book and came up with 125 -128 MBH depending on what numbers I used for a few odd ball radiators that had been replaced over the years. 
They question is am I looking at the numbers on boiler specs correctly? 
For example: 
Slant Finn Galaxy

CSA Input 120 DOE rating 98K BTUH 
CSA Input 160 DOE rating  131K BTUH

The DOE rating of the 160 gets me close to 128 MBH i've calculated. 

When I look at a Utica PEG series

112 MBH Input and 93 MBH output

150 MBH Input and 125 MBH output

The 150 gets me in the range of MBH i've calculated. 

Im probably over thinking it, but just wanted to verify i'm looking at things correctly. Haven't sized a new steam boiler in years mainly just service. Not many resi steam experts in the supply houses in the Detroit area anymore and it's slim pickings on brands that are carried in this area. 
Utica
Velocity Boiler
Slantfin
Burnham ( New Yorker) 

Jamie Hall

Which Galaxy? But you are overthinking it. The boiler should have a "square feet of steam" rating or wording like that. Compare that to your EDR -- and stop right there.

KC_Jones

What is the EDR of the system?  Why do all the contortions converting to BTU, when you can just look it up by the EDR?

I’m of the opinion slightly smaller is better than slightly bigger.

CMadatMe

Never size a Steam boiler by btu/hr. Always size by Sqft of EDR. Not all boiler chests are the same.

offdutytech

My EDR was 298 to 310 depending on the numbers I used. 
The Slant Fin Galaxy was GXHA-120 because of the piping configuration and price. 120 MBH with 304 Sqft. This looks like it gets me very close to numbers I ran. Prob was just over thinking things

JUGHNE

Out of curiosity, I would clock the meter on the old boiler just to see how oversized it might be. This is not a method to size the new boiler, rather just for comparison.

Is that a counter flow main? They put a drip/equalizer on the bottom of the main.
Are there any wet or dry returns other than the drip?

I see the screen door spring on the burner door, for delayed ignition relief; from what I have been told.

ratio

JUGHNE said:

I see the screen door spring on the burner door, for delayed ignition relief; from what I have been told.

I miss the good old days!

offdutytech

Looks to be counterflow. Here are some more pics. There's a Taco number 0 water heater on the rear of the boiler I'm assuming to warm the condensate up? It's been years since I've seen one.

EBEBRATT-Ed

Looks pretty easy piping wise, somebody did the header right. Pipe the new boiler with it's own header ans the mFG want's it and feed the old header from that and you should be fine. No need to dismantil all the old stuff. Leave the old drip/equalizer as is and put a new equalizer on the new boiler.

That old heater looks like a tank heater for domestic hot water probably heated a storage tank that was removed.

Just use your EDR # and compare that to the boiler you pick, no need for any calculations as others have mentioned

BobC

Years ago when i was still on oil oil, I heard a bang from the cellar. i went down and found the Field draft regulator had been blown across the cellar. That had never been screwed on, it was just stuffed onto it's mounting collar. I put it back on with screws and ordered a new ignition transformer to replace the weak one I had been procrastinating about. I had noticed a few hard starts and when i tested the transformer the spark was pretty feeble.

It worked fine after that so my suspicions about the transformer were right.

Bob