Steve S wrote:
Now that my heating controller is nearly done I've been using it to collect
data. Some of it is quite surprising, at least to me.

We have a ~25 year old 120L HW cylinder with foam insulation. Over a period
of 6 hours with no heat input (and just a couple of handwashes) the
temperature dropped from 61.5 C to 56.5 C. Measurements have a resolution of
0.1C. According to my calculations that represents a loss of ~2.5
megajoules, which over 6 hours is an average of ~115W.

I daresay modern cylinders could do a lot better than this, but somehow I
was expecting the losses to be higher.

Steve S
--

That fits well with my observation that I can heat our DHW all summer
and barely be able to measure the oil used (hand washing, washing
machine and dishwasher). Come autumn and the start of the CH season we
use about 1cm a day.
It really makes me wonder how these solar systems which basically just
do DHW can ever be justified.