Boiler Primary Pipe Size

Earthfire

what does the BOILER MANUFACTURER specify ???? That should be your minimum Not what the supply house has on the shelf.

Keith B Carpenter

Boiler Primary Pipe Size

I am estimating a boiler replacement w/ a new hot water boiler w/ a net output of 360,000 BTUH's. What is the proper Pipe size when the Boiler Manufacturer wants 2 1/2" minimum pipe, the pipe size recommened according to several charts by B&G and others should be 2" but the properly sized Circulator comes w/ 1 1/2" flanges? The boiler primary loop is very short giving us a low head / high volume Circulator.

JIM F.

pipe size

a 2" header will handle 450mbh with a 20 t.d the gpm should be 45
a 2 1/2" header will do 750 mbh @ 75 gpm with 20* t.d.

Terry

pipe size

I'd probably use a 2" Line size and not worry about reducing to 1-1/2" @ pump flanges.

DanHolohan

There's really no reason

to base primary loop pipe (or pump) size on a 20-degree temperature drop. A 40-degree drop is more like it.

Based on the writings of the late, great Gil Carlson, I did my best to make a case for this in "Primary/Secondary Pumping Made Easy!" No sense in leaving money on the job, especially when you don't get any advantage.

Earthfire

primary piping

With todays smaller mass water boilers(heaters)wouldn't it be more beneficial to size the (primary) near boiler piping loop and bypass to manufacturer specs? based on the need for minimum flow volumn thru the heat exchanger?or wouldn't down sizing the pipe as in this particular question from 2 1/2in. to 2 or 1 1/2in. creat a flow /turbulence situation in the boiler at the inlet and outlet??? An possible example of that would be Glenn S's comment about piping location in a thread a couple of days ago??? all secondary piping would then of course be sized to the load served by the particular loop.

DanHolohan

I'll check to the manufacturer, of course,

particularly with the copper-tube folks, but I can't think of a reason why, if a boiler can take a return temperature of 140 degrees, that a primary/secondary system can't be made better by working with at least a 40-degree temperature drop across the primary. It reduces the size of the pipe and the primary circulator, and this begins to make a real difference when that primary stretches beyond the boiler room.