"dennis@home" wrote in message
...
On 25/09/2018 19:49, 543dsa wrote:


"Chris J Dixon" wrote in message
...
Jeff Layman wrote:

Just fitted some insulation
(https://www.screwfix.com/p/hot-water-cylinder-jacket-18-x-80mm-x-1219mm/43483)
over a hot water cylinder which already had about 25mm of foam
insulation.

With existing tank insulation, can anybody do the maths to work
out how much difference the extra lagging will make?

I might well try to do the same, if there is any significant
benefit.

Not really possible to do the maths in isolation.

You'd have to actually measure how quickly it cools
with the electricity turned off, with and without the
extra insulation, to see how long it would take to
pay for itself and if it actually would.

wrong as usual

We'll see...

its quite easy to do the maths.

Not when you dont have the numbers to use.

its done the same as electrical resistance.

however its easier to use something like

www.vesma.com/tutorial/uvalue01/uvalue01.htm

Pity that that doesnt tell you the actual u value
of the original tank, or the added blanket given
the impossibility of allowing for how well it is
fitted around the pipes and thermostat etc.