Undecided ... electric only

coffeehound

macman said:

Have you looked at switching to a competitive E7 tariff and ditching the E10? Are those extra 3 hours really crucial?

E10-spec’d NSHs could be a problem

Energy28 said:
He suggested 180 or 210 litres. Do you think that these sound about a good size?

If in doubt, go larger. Gerry1’s estimate suggests 4 minute showers for four. Perhaps 250 litre would provide nearer 10 minute showers giving more leeway.  New unvented cylinders lose very little heat so it will not cost more to run a larger tank

Energy28

Gerry1 said:

Back of envelope calculation: 12 litres/minute shower, assume 60% hot water because it'll need to be mixed with cold to avoid scalding, so 7.2 litres/minute of hot water.  For four people, that allows showers of four minutes each, but that's with no allowance for washing up and hand washing.

Sounds like you need a bigger hot tank.  Make sure the floor can withstand the load !

Thanks Gerry

If I get an unvented direct hot water cylinder what size would be worth considering ... 180ltrs?

Energy28

coffeehound said:

macman said:

Have you looked at switching to a competitive E7 tariff and ditching the E10? Are those extra 3 hours really crucial?

E10-spec’d NSHs could be a problem

Energy28 said:
He suggested 180 or 210 litres. Do you think that these sound about a good size?

If in doubt, go larger. Gerry1’s estimate suggests 4 minute showers for four. Perhaps 250 litre would provide nearer 10 minute showers giving more leeway.  New unvented cylinders lose very little heat so it will not cost more to run a larger tank

Thank you.

Feel like this is a good option. Very grateful for your help.

Reed_Richards

See here https://www.hotwater.org.uk/sizing-a-hot-water-cylinder/ , particularly the last paragraph.  You'll want to do all the heating at night using cheaper electricity, I presume.  If so, the cylinder needs to be a bit larger than it would be for a gas boiler where there is no penalty in topping-up the heat during the day.

Gerry1

coffeehound said:

If in doubt, go larger. Gerry1’s estimate suggests 4 minute showers for four. Perhaps 250 litre would provide nearer 10 minute showers giving more leeway.  New unvented cylinders lose very little heat so it will not cost more to run a larger tank

Yes. it's better to go for a larger size if you're not sure.  If it turns out you were over-cautious, the extra cost will be relatively small and soon forgotten, whereas it'll be an ongoing source of irritation if the water often goes cold and it would be much more expensive to correct later.  Having a greater hot water capacity may also prove useful if you have friends or relatives to stay.

Another consideration is that a greater hot water capacity will be more suitable if you decide to switch to E7.  E10 tariffs may well be phased out or made unaffordable, so E7 may be the way to go, especially as it's available from far more suppliers.  At least with E10 you'll have hot water again in the afternoon if you run out but that won't be the case with E7.

When there's a cold snap next winter, try running the NSHs for just seven hours by switching off the three hour boost each afternoon.  That will give you a good idea of whether a stright switch to E7 would be realistic.  If not, you could consider replacing a existing NSH with a modern high heat retention one (or adding an extra NSH) so that you can always get the required storage in only seven hours.  It's best not to assume that E10 will continue to be available at affordable rates, so plan everything with that in mind.

Energy28

Thank you everyone for all your help and advice.

So very grateful!

coffeehound

Gerry1 said:

Yes. it's better to go for a larger size if you're not sure.  If it turns out you were over-cautious, the extra cost will be relatively small and soon forgotten, whereas it'll be an ongoing source of irritation if the water often goes cold and it would be much more expensive to correct later.  Having a greater hot water capacity may also prove useful if you have friends or relatives to stay.

Another consideration is that a greater hot water capacity will be more suitable if you decide to switch to E7.  E10 tariffs may well be phased out or made unaffordable, so E7 may be the way to go, especially as it's available from far more suppliers.  At least with E10 you'll have hot water again in the afternoon if you run out but that won't be the case with E7.

Another advantage of a generously-sized DHW cylinder is that it could allow the thermostat to be run at a lower temperature.  Although the current recommendation from most sources is to set it to 60 ℃, I suspect that might get reduced to 55 º in the future.  It's interesting that in the USA, the recommended minimum figure is 120 ºF which is only 48.9 ℃.  Some manufacturers here already supply immersion heaters with the T-stat set to 55 º.