sizing boiler Home › Forums › Public Forums › General Plumbing › sizing boiler This topic has 1 reply, 2 voices, and was last updated 21 years, 9 months ago by Harold Kestenholz. Viewing 1 reply thread Author Posts 6 Aug 2002 at 12:53 am #275704 MasterPlumbersKeymaster I got 110’of fin tube 12’of cast iron baseboard and i am adding a indirect water heater what size boiler do i need. 6 Aug 2002 at 2:06 am #292747 Harold KestenholzParticipant You need an 80,000 btuh IBR rated boiler. This is about 100,000 Btuh input. Author Posts Viewing 1 reply thread You must be logged in to reply to this topic. Log In Username: Password: Keep me signed in Log In