Eep - shower pump, what size pipe?

Hello All
Just learned the connector sizes for shower pumps are 15mm (screwfix don't print 'em, only by searching for spec sheets I found out BEFORE I ordered the pipe).
I was going to do the run from the HW and CW tanks in 22mm before and after the pump to the shower - but if the pump is only 15mm, is it worth it? Am I better advised to run the whole run (some 10M) in the smaller size?
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Simon Avery, Dartmoor, UK
uk.d-i-y FAQ: http://www.diyfaq.org.uk /
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Don't think of the resistance in the pipework as being as bad as the weakest link. Every bit of 15mm pipework adds resistance. Every bit of 22mm pipework adds a lot less. You will get much less resistance piping in 22mm overall with such a length even with the 15mm pump.
However, it may be worth calculating the significance of the likely pressure drop/flow rate, as there are some advantages piping in 15mm. In particular, you lose less heated water every time you turn off the tap and you get hot water to the tap quicker.
If it was me, I'd probably use 22mm for a bath (or multiple outlets), but 15mm for a simple shower/basin, as the flow rate is much lower for a shower and probably can cope with the restriction when pumped.
Christian.
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