Blending valves for DHW

[John Rumm]

Anyone used/owned a "whole house" 22mm blending valve on the outlet of a stored water system?

Worth having?

Effects on flow rate?

Any brands to recommend / avoid?

May be ripping and replacing the current conventional cylinder with a Unistore unvented unit shortly. The current one is undersized and is hence run a little hotter to maintain adequate energy storage - but this makes the hot water rather too hot at basins etc. The new one will be larger, and given our hard water, probably run at no more than 60 degrees.

[gremlin_95]

If you're going to use Vaillant controls then it is probably worth it, the weekly legionella killing cycle causes scalding hot water, though it can be disabled. You can choose what time you want it to carry out the cycle though, I find it best when no one is going to use the hot water as its supposed to hold the tank at 70ºc for an hour.

[John Rumm]

Yes, good point. According to the specs for the 210L cylinder, it only loses heat at about 80W... at that rate it would take days to get back to 60 if you don't draw off much water!

[dennis]

Only 80W, that's more than 2kWhr a day, it needs another foot of insulation around it.

[John Rumm]

1.9 according to its spec. Should be enough to keep the airing cupboard warm, and not having the extra foot of insulation will mean there is space for clothes as well.

[Fred]

I hadn't thought of this before. Does increasing the temperature make a big difference to scale formation? I know chemical reactions are faster when it is hot, but would 10C make that much difference in this case?

[Andy Dingley]

Yes. Calcium sulphate is the problem, as this is what forms hard scale. It starts to precipitate from about 60 C and increases with temperature.