sizing a steam boiler

dan68

i did a radiator sq footage brake down and came up with 370 sq ft that with 10% for piping what is the next step to find the input btu somthing about multiplying the appropriate emission rate by total sq ft how do i find emissions rate thanks dan

Jamie Hall

BTU per square foot

multiply the EDR by 240 to get the net BTU you need at the radiators.  Then I would use a 1.33 pickup factor to get the BTU output of the boiler.  Most boilers also have net I=B=R output rating for a particular size shown.

jpf321

in most cases ..

you can stop right at 370 .. and check the sq ft of steam that the boiler rating shows. this rating includes 1.33 for pickup factor and unless you have an exotic pipe system, 1.33 should be fine.



next questions are fuel type? gas? oil? dual? other? tankless coil or not?

Charlie from wmass

Do as Jamie says.

From someone who does this for a living the 1.33 factor seldom makes for an over sized boiler and seldom is "normal" piping normal.

jpf321

confused...

how are the methods above different. my method simply requires 1 less bit of math (sf X 240 X 1.33 = BTUH Output) but the boiler ratings already do this math in their sq ft column. so i'm not sure how Jamie's method is different. I was simply reiterating steamhead's advice to me in his post/thread here: http://www.heatinghelp.com/forum-thread/128987/oil-now-gas-later#p1183969 I think he also does this for a living. 

Charlie from wmass

Not meaning to sound crabby sorry

Jeremy I was trying to post a quick reply with the kids on vacation this week I am running more than usual so I was simply saying I add the .33 to what I total for the system to get the boiler size. It may be a regional thing but if I do not in the Berkshires it can get very marginal on boiler sizing on those cold February nights. I feel areas of warm climates can cut it closer with boiler size. I am not promoting over size boilers but It is often a 5 section high fire vs a 6 section low fire in a residential boiler. I had one boiler I sized with out the pick up factor and it is very marginal in filling the system with steam. so much so one large radiator never quite gets hot all the way to the end before the home is warmed up. This is with the best of venting and a clean dry return system on a one pipe steam system. This is also the only steam boiler I had sized by a supply house. I was busy and they pushed to do it for me. I think they took the wrong values for a few of the less common radiators so I ended up installing a 5 section high fire when I had wanted to use a 6 section low fire boiler. so that would be roughly 480 sq ft which drops it between sizes on the gas boilers. I am wondering is that 370 just the radiators or the radiators plus 10 %?