I've been told I need a 25/6 rated circulating pump for the central heating. What doe these numbers mean exactly. I want to know because I discovered my existing pump is rated for a 6m head.

1 Answer 1


It has been a few years since I looked at specs on one but the two numbers are identified as Q/H or (m3/h by m). (m = meters)
To my understanding Q is volume of flow in m³/h (25), so how many cubic meters of liquid can flow in a hour period.
With H is delivery head in m (height) which is the height you can pump a liquid to straight up.
These are the basic description for standard values. In an exact case to determine what values are needed in a specific application would be based on all the variables such as pipe sizes in the entire system, desired pressures, suction tank/source levels and more.

  • thanks - have you any idea why so many are sold as 25/6 but there seems to be no other ratings ( that I can see visible in the ads). Commented Oct 20, 2016 at 20:43
  • I would only render a guess that common applications for most part are standardized or have regulation limits. On a quick look I see a few variations. Commented Oct 20, 2016 at 22:06

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