Boiler sizing based on Heat Loss Calc and Length of baseboard

kgk14

I am an average homeowner who has been researching boilers and hot water heaters for over a month and close to a decision to replace an old tankless oil burner. I am seeking feedback from the 'The Wall' on understanding the connection between the results of a heat loss calculation and the length of cast iron base board in the house.  The heat loss calculation was 85,274 BTU. Some installers say that the 123.3 ft. of cast iron baseboard and 20' of sheet metal baseboard in the house can only put out about 66,000 BTU of heat and the new boiler should be sized at that size.   Which view is more accurate?  The old boiler is a Burnham Jubilee. 

icesailor

Heat Loss Sizing:

Whether you have a total of installed radiation of 10' or 1,000', it doesn't matter how much or how little. The boiler must be sized according to an accurate and comprehensive heat loss of the structure.

I understand that Slant-Fin still offers their free heat loss program. Heat loss Explorer or something like that. It is based on one of the oldest methods around, the IBR H-22 heat loss guide that was part of a course to teach Wet Heads how to design and install hydronic heating systems.

kgk14

Found the App

and spent a couple of hours measuring and punching numbers.   The H/L came out to be about 66,000 BTU and even with a 10% fudge factor, a 74k net BTU boiler should work fine.   Thanks to Slant Fin and the advice!