DIYbanter - View Single Post - What are currently your best saving tips ?

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On Sat, 15 May 2010 13:58:53 -0700, "Bob F" wrote:

Tim Watts wrote:
On 15/05/10 19:34, zzzzzzzzzz wrote:

So you waste the water in the pipes either way. If you're washing
by hand (with hot water) you're wasting all the hot water needed to
get the tap up to temperature, plus the water needed to do the
dishes. Seems like an even stronger argument for a hot-water plumed
dishwasher.

No, because 10m of 15mm dia pipe contains 1.7 l of water. A typical
model 60cm wide Miele dishawasher takes in 13l of water over several
fills over 1-1.5 hours.

If it takes 4 fills (I haven't counted) that's about 3l of water per
fill so half of that is cold either way and the central heating has to
heat that half just to waste it cooling in the pipe and the machine
has to heat the other half from cold effectively. So it's hardly worth
bothering with.

Things may be worse with a combi boiler that actually has to fire up
to produce hot water from cold mains - there's now pipework wastage
and cold coming from the boiler while it gets the heat exchanger
warmed up.

If the pipes are insulated, they don't lose that much in one run. Heating water
with gas here cost about half what letting the dishwasher heat it electrically
costs.

Few pipes are insulated, and even fewer in walls. All pipes, no matter how
much insulation, will lose the heat in the entire run each cycle.