very general but.......

Jim_64

in primary/secondary piping with a modcon; if the original, non-modcon piping had three zones of, 1-1/4", 2", and 3/4", should the stock returns/supplies of 1-1/4" be increased to 2" or more of main?

Mark Eatherton

Size it to the load...

Not the pipe size.

If it was a gravity h.w. heating system, it had big pipes to reduce pressure drop on flow. The actual connected load, based on a 20 degree delta T is what the piping needs to be sized for. And the load, in a hot water heating system, does not necessairly mean the EDR of the connected radiation, because energy conservation efforts may have been instituted.

As a basic rule of thumb, Dan instructs that on a gravity conversion system, that the pipe size, divided by two, then one pipe size lower is adequate at the near boiler piping.

So, IF your 2" main WAS gravity and is being converted to a force system, 2" divided by 2 = 1", and the next pipe size down is 3/4", hence the near boiler piping serving the 2" pipe would be 3/4".

If in fact the pipe does need to be 2", then yes, your header should start out 2", then taper down to the minimum size.

ME

Jim_64

thanks mark

due to the age of the building, it had to have been a coal fired gravity system, with a 2" blk pipe main, and then converted to oil and pumps. and here's where it gets
'peculiar'; a weil mod was installed and the original pumps were used, where the current 'main loop' is 1-1/4cu and the zones are Teed off to the original 2" blk, a 1-1/4" cu, and a 3/4" cu. of which, all the zones are standard, finned baseboard or free-standing convectors. and if this helps; picture a weil ultra with the standard 12" suppy/return separation, Teed main of 1-1/4cu, and off of the 1-1/4" suppy/return main, the 2, 1-1/4, and 3/4 zones are Teed from, respectively with their individual pumps