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Boiler choices and sizing.
House is 1950's build, open floor plan. Half brick, low pitch roof with no attic. 2/3rds crawl space and 1/3 slab. All windows replaced 2016 – double pane low E, high quality vinyl. New roof (2017) w/1-1/2” insulation board (this really tightened up the house).
132' of BaseRay cast iron base board radiators. These seem smaller than the 9A model, only about 6-3/4” tall. One BaseRay slenderized radiator 5 tube, 1-3/4”ctc, 25” tall with 14 sections in kitchen and one BaseRay slenderized radiator 6 tube, 1-3/4”ctc, 32 tall with 6 sections in the utility room.
Currently have a 25-some year old Lochinvar RBN 135. I don't know what the Lochinvar replaced but I remember it had to broken up into pieces (gigantic cast iron) to get it out of the utility room.
My own boiler sizing by the radiation method says I need about 55.5MBH.
The Slantfin contractor by manual J method says I need 53982MBH.
The Weil-Mclain contractor says by manual J (different software, I asked) that I need 57556.
I believe both of them. Pricing is similar for both.
Which boiler will be the most reliable for the next 10 years?
Gas fired, chimney vented SlantFin Sentry S-90?
Gas fired, chimney vented Weil-Mclain Cga4?