On 25/09/2018 19:38, Chris J Dixon wrote:
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?

Depends how much you have already but as a rough rule of thumb if you
doubled the thickness using the same material then the rate of heat loss
through it would he halved. However, conduction along pipes in and out
of the hot zone make it somewhat less effective than that.

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

£30 spent on better insulation round the hot water tank pays for itself
with the fuel savings in the first year. It also means that your hot
water stays warmer for longer when the heating isn't on.

--
Regards,
Martin Brown