size of steam boiler replacement

luke

i am installing a new steam boiler to replace a 300,000 unit in a 4 story townhouse. i measured the exisitng radiators and came up with 350 sq feet of radiators only (no piping load). almost all of the piping to the radiators is exposed over several floors and the residents seem to really like this because it distributes heat evenly and reduces the need for bulky radiators, so I do not want to re-insulate the pipes.

in each floor below the top floor there are about 9 exposed pipes, most of them are 2 diam. The rule of thumb for piping seems to be 33% of the radiator load--what would you use instead given that none of the pipes are insulated.

scrook_2

Steam Boiler Sizing

Wow, 300,000 BTU/hr boiler and only 84,000 BTU/hr of radiation (excluding uninsulated risers!

Are the exposed pipes about 2" in diameter (1.90" O.D. therefore 1 1/2" pipe) or are they 2" pipe (2 3/8" O.D.)?

From Burnam's Heating Helper: at 70° air temp a 1 1/2" pipe looses about 173 BTU/hr per foot (0.72 sq. ft EDR per ft) and a 2" pipe loses about 212 BTU/hr per foot (0.88 sq. ft. EDR per foot), so you can measure them and get the equiv additional sq. ft. of radiation and add that to the 350 sq. ft from the radiators.

Say they're all 2" pipes and all 8' long: 9*8*0.88=63 sq. ft. additional. 1.33 times that gets you your required boiler output, around 132,000 BTU/hr output for the example sited.

luke

thanks for the input. It would appear that the pipes will add at least an additional 200 sq feet to the system. I can follow your instructions but have one additional question. assume I calculate the edr of all the exposed pipes as an additional 250 sq ft. and this 250 includes all the piping in the building and it is all exposed. then my total sq feet is 600 is it still necessary to multiply the 600 by 1.33 for a loss factor or have I already accounted for that loss factor by individually adding together all the pipes in the system?