Boiler size

Brad White_185

I always find it helpful to double-check things but let's assume that your EDR take-off is correct.

Find a boiler that has that EDR rating, often listed as an I=B=R rating in square feet. That boiler, specific to I=B=R, includes 33 percent (1.33 multiplier) on top of your net radiation EDR number. This is to account for piping and pick-up losses.

I would not size a boiler for more than that number, at least not by much. Pick the boiler that meets or just exceeds the connected EDR and let the boiler take care of the piping and pick-up losses.

It goes without saying (and not that this will stop me), that proper near-boiler piping, venting, low pressure -under a pound should do it- and pipe insulation go a really long way to getting you good, dry, fast steam heat.

SpeyFitter

Boiler size

We’re replacing a very old boiler for a 2-pipe steam system in a 20-unit, 5 floor apartment building. The old boiler has a nameplate I-B-R rating of 5300 sq. ft. steam. Suspecting that the old boiler is oversized, we did a survey of all the radiators and convectors and come up with 3250 sq. ft. EDR. Should we go close to the EDR number for the new boiler, or might we run into problems with the amount of time it takes to get steam to the end of the mains and a heating imbalance between units that are close to the boiler and those at the end of the lines?