Tim Watts wrote
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.
They dont necessarily heat all those fills tho.
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
Its rather more than half because some heat
is lost from the second half heating the pipe.
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.
And has to heat even the hottest water even more too.
So it's hardly worth bothering with.
Particularly when you consider the baking on effect below.
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.
There is a stonger argument for a washing machine having a hot fill as they use around 55 litres of water for a wash
But most clothes washing works fine in cold water. Dishwashing doesnt.
- but that's something to do with (supposedly) the modern detergents preferring to work from cold with a gentle warm
up in the machine.
Its not actually the detergent. Starting with cold
water avoids baking the food onto the plates.