boiler sizing Which is better too big or too small?

sethspma

 I need to replace my current boiler as it is very inefficient./old.  I'm ready to purchase one of the higher efficient models out there.  My current boiler AGA INPUT = 216, AGA OUTPUT = 172,800, & the NET IBR = 129600.  There are 2 boilers I am considering. Both are Weil Mclain Ultra's.  The Ultra 155 has a NET IBR of 123,000 BTU, and the ULTRA 230 which has a NET IBR of 183,000 BTU.  My question is: Is it better to go with the one that has slightly less than I currently have, or Go with the one that is Far above it?  My home is 3500 square feet, 90 years old, and has new windows, and new siding.  The BTU Calculator is also confusing as it says I require 192,000BTU (Which I am guessing is not NET IBR?)

ced48

Neither-Do a Heat Loss-

The size of your old boiler does not matter, it was most likely oversized, but who knows. When you have the heat loss info, then, and only the, can you size your new boiler.

nicholas bonham-carter

Boiler choice

What sort of system have you? Go to the Slantfin boiler website and find their heat-loss survey software. Use that to find the heat-loss of your house.

If you have steam, it's a different procedure, but still possible for you to do.--NBC

sethspma

Boiler choice

I currently have a VERY old American 9-w-99a 2 zone boiler system.  I have no idea of the heat/loss.  I guess I'm going to have to figure all of that out from the sounds of it.  Just trying to get it ordered as I'm running out of time.