Boiler Sizing

Steve Nichols

Am getting quotes for replacing my original (i.e. very old) 1 pipe steam system boiler.  I have done the EDR calcs based off of Dan's book.  The house contains only convector units that are mainly recessed units.  I have come up with 255 square feet of steam and when 1.33 pickup factor added in, I get 339 square feet.  This equates to 81,556 BTU.  The most recent contractor wants to put in a Burnham IN5 since he feels theload is too close to the upper limit of the IN4 (rated for 271 square feet @ 65MBH using the I=B=R Rating).

The IN5 ratings are (358 square feet of steam @ 86,000MBH  using I=B=R rating). I am thinking this is too much boiler for my heating load, but I'm not a professional.  I don't want this thing to short cycle but I'm not sure if I'm too close to the upper limit of the IN4 capacity. 

Thoughts, ideas, comments?

gerry gill

dont add in any extra for piping

as that is already factored in by the factory as long as you use your actual square footage and size the boiler to its square foot rating. did that make sense?

Steve Nichols

So IN4 it is?

Thanks Gerry,

So, I should be okay if the square feet is up to the max. advertised IBR rating of the boiler?  I'm just wondering how much "wiggle room" is needed for calcs that are off a bit.  I'm close to the upper limit of the IN4 but  well below the IN5.  Just want to make sure I order the boiler that best fits my heating load. 

Nice webpage on massive venting, by the way!  I just ordered up some Gorton #1's to do my mains.

The Steam Whisperer (Formerly Boilerpro)

The smaller boiler should be just fine...

you have a load of 255 EDR and the boiler can handle 271.  If they are lightweight copper/aluminum convectors, the pick up load is very light, so the 1.33 muliplier is probably very conservative, giving you even more extra capacity.

Steve Nichols

Thanks!

Heating Help forum to the rescue again. 

Yes, they are the lightweight style, so I sized it right (yay).

Thanks Everyone for the much valued input.



Steve