I was browsing through some old posts (there are so many here; how do
you choose what to read?) and I read about hot water circulating pumps
that are supposed to get hot water to the taps quicker.
This sounds very good. In our house the HW goes from the cylinder to
the bathroom, then drops into the kitchen, where it goes into the
concrete floor and over to the sink. None of it was lagged. I have
tried to lag various parts when I have had different floorboards up
but obviously the run under the kitchen floor is inaccessible. It
takes ages to get hot water to the kitchen sink. One of these pumps
might be a good idea.
However, I am unsure how they work. Do you need to run a return pipe?
Do they constantly circulate hot water around the house? If so that
would be very impractical because surely you would need to plumb the
hot water in a ring main, rather than the traditional radial style and
have a return pipe? Also wouldn't this be uneconomical because you
would constantly be losing heat through the pipe work rather than
keeping it in a well insulated cylinder?
Or is it that the pump only comes on when a tap is open and just
increases the flow so that the hot water gets there quicker, like a
Is there a special pump for this purpose and what are they called?
Yes, typically smaller than the main feed pipe so you could run it in
8mm or 10mm copper or 10mm plastic.
Well, that's what you have to do if you want such a system. It's more
commonly used in larger, commercial or industrial premises.
Yup, but then you don't throw away heat and water running off warm water to
get it hot.
No it runs constantly (preferably on a timer so at times of low demand you
can still get got water (if it's available) but you have to run off the
Usually bronze pumps (though plastics and stainless steel might be used)
You'd lose even more heat circulating constantly-hot water through
uninsulated pipes in screed. Since you'd have to run new pipework for the
return ayway, I'd suggest scrapping the existing pipe and installing a new,
more direct run of well insulated pipework. You could use plastic for easy
A pipe stat can be fitted when the loop is up to temperature and it switches
off the pump. IF a mains pressure loop the instant hot water can be used for
kettles reducing the electricity bill, so offsetting the running cost of the
pump. If on a water meter it also reduces water waste and again cost
offset. Also instant hot water into a washing machine. Many just fill up
the machine with cold water from the dead-leg DHW draw-off pipe and then the
expensive to run electric element kicks in. And the great convenience of
having instant hot water at taps. So,they are not financial dead loss.
Well worth doing as long as the loop is very well insulated and a pipe stat
I just checked on the John Lewis web site - a random selection of four
washing machines (3 A+ and one A rating) - all cold fill only. Are any
new washing machines hot & cold fill?
They (JL) say that cold fill is better because the hot water fill would
normally be at too high a temperature so would require cooling down (for
That said, if they are available, hot and cold fill might be more
economical for those who do a large proportion of hot washes for some
Decent machines do not allow hot in on settings below 60C, so that is crap.
I know most dishwashers are cold fill only, but some will allow hot fill and
this means a hot rise too. It is more economical overall even though the
rise is hot, that heating the water with electricity all the way. It is also
quicker as the machine does not stand while the element heats the water.
In the USA most machine many w/machines have no internal heaters relying on
the water temp from the house, so it makes the product cheaper. Makes sense.
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