On Thu, 13 Oct 2005 14:03:48 GMT, "Mark Schofield"
wrote:

On a new Weil-McLain WTGO3 boiler servicing three zones (Taco zone valves),
should the single circulator be piped in the supply from the boiler to the
zones or in return from the zones to the boiler? The current boiler, which
is to be replaced, has the circulator in the return line. However, the
contractor/supplier suggests pumping away from the boiler. the reasoning for
the placement would also be appreciated.Thanks, Mark S.


Circulators for residential systems used to be mostly placed in the
return side. The reason for this was they would be pumping somewhat
cooler water which was easier on them. Modern circulators are usually
rated to handle much higher temperature water than they ever see and
can be placed on the outlet side of the boiler without shortening
their life.

From a hydraulics perspective, you want the inlet of the circulator to
be as close as possible to the connection point of the expansion tank.
This means at the outlet of the boiler. The short explanation is that
placing it there *increases* the pressure in the piping system when
the circulator is running, while placing it at the inlet of the boiler
*decreases* pressure in the piping system when it is running. Among
other things, this makes it easier to vent the system, and entrapped
air causes less trouble.

If you want the gory details, look for Siegenthaler's book: "Modern
Hydronic Heating", which you may very well find in the library.

HTH,

Paul