two central heating pumps

[Best]

Then what does metres head of a pump indicate? And why do many small system boilers come with 6 metre pumps? A 5 metre pump will not pump well on a 3 story building.

 

[doitmyself]

Then what does metres head of a pump indicate? And why do many small system boilers come with 6 metre pumps? A 5 metre pump will not pump well on a 3 story building.

Metres head is one way of measuring the pressure the pump is able to produce. It could also be measured in Bar or Kilopascals.

If you connect a U-gauge manometer to the output of a circulator this will show the pressure produced. Just like measuring the pressure of a gas supply.

The reason for installing 6m pumps in many system boilers is that modern heat-exchangers have such a high resistance that a 5m pump would have very little pressure left to circulate water through the rads.

The pipes for a 3 storey building will be longer than for a 2 storey so the pressure loss will be greater, which will require a pump with a higher head.

 

[Chuck]

Then what does metres head of a pump indicate? And why do many small system boilers come with 6 metre pumps? A 5 metre pump will not pump well on a 3 story building.

It refers to the pressure difference (6m H2O, i.e. 0.6 bar or 60kPa) between the pump inlet and outlet at which the flow-rate (e.g. in m^3/hour) has fallen to zero. You can see for yourself by looking at the 'pump-curves' published by the manufacturers. For example:

https://uk.grundfos.com/content/dam/UK/Brochure/UPS2 datasheet 1214.pdf

It's not always true that 'A 5 metre pump will not pump well on a 3 story building'. When it is true it's because the pipework / radiator / pump sizing has been got wrong.

 

[Best]

Thanks for both explanations.
I understand the 6m pumps were thought to be needed for modern heat exchangers. I also know the head of a pump can be thought of as the resistance.