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Boiler replacement question: Two staged boilers setup vs one large with a 2 stage gas valve
I am a Denver homeowner with a large two pipe steam system - Well McLain(EGH-85 349K BTU Input) boiler, 10 various sized convectors and 5 big radiators. The system operates at 8-12 Oz of pressure controlled by Vapourstat. The boiler is about 15 years old and last April started leaking between the sections. Currently we are deciding how to best replace it.
In the winter half of the radiators/convectors are turned off as we don’t use the rooms. That in turn makes the boiler to shortcycle(5-10 min) which creates uncomfortable heating. The aim is to have replacement boiler/boilers that can handle varying heating requirements better. The EDR survey was done - 980 sq.ft EDR. Adding the pickup factor(x1.33) and 5500ft altitude correction(20%) it was determined we need a boiler/s with an input of over 450k BTU. Since the old 349K BTU boiler was heating the house with all radiators on pretty well I think the 450K BTU is too much and that max of 400K BTU total input should be sufficient.
After that overture I would like to ask for your expert opinions what boiler setup is best under my circumstances – one large 400K Btu boiler with added 2 stage gas valve or 2 smaller ones (60/40) staged by vapourstat with possibly 2 stage valve on the bigger boiler? The smaller boilers will just fit trough my narrow boiler room door while the big one needs to come disassembled.
My installer prefers Peerless and the local rep told him that the warranty of the boiler will be voided if retrofitted with a 2 stage gas valve as it doesn’t come as an option on smaller steam boilers. Since the 2 boiler setup will cost 50% more is it really worth and what are the advantages?
I would appreciate your help.