When is it cheaper/ best to heat a hot water tank?

LangleyAgent

 Have a gas boiler that gives heating and hot water. 

Was wondering if anyone knows if it is cheaper / more efficient to run it for hot water over night, when have a cheaper tariff or when the heating is on, as the boiler is already working?  Or does it not make any difference whatsoever?

born_again

What sort of boiler?

Ectophile

There will be a little electricity used to power the boiler and pump.  So that would be cheaper at night.  The gas costs the same any time of day.

Scot_39

What tariff do you have that gives you a discounted night rate on gas ?

The cost of running the pump on the indirect coil circulation is probably trivial compared to the kWh needed to heat a tank (small 100l maybe 7 kWh from cold - a large 240-300 - pro rata upto maybe 20kWh - how many would empty to that extent ?)

And most people with gas wouldn't use conventional time of use - are you an Octopus agile (electric only) user ?

Tanks themselves can be lossy - even the best modern 1-2kWh over 24 hrs - so probably best to heat before main demand - when you need the water hottest - my losses are probably half my daily demand for HW.

Never really read anything here on gas hw / vs hw/rads in parallel efficeincy - lets see what those in the know say.

Supect the relative efficiency of heating hw or hw and rads in winter - might pale by comparison to tank and pipework losses - but it's an interesting question.

LangleyAgent

It's a Worcester Greenstar 30CDi classic system

LangleyAgent

Octopus overnight cheap tariff, only for Elec, as someone said, Gas same price whenever. 

Just wondered if there was any difference to save costs or make efficient use of heating the water for the tank when the rads are on. 

Scot_39

If your on a conventional E7 type deal at Octopus - and have gas ch and hot water - you might be throwing money away.

Many only looked at their old E7 style peak / off-peak balance when prices went up in last 2 years - some were using as little as 10-15% off peak - and so paying 3-4p per kWh on average more than could be - adding upto £100 per annum to bills at duel fuel cap TDCV (2700 kWh pa) use

You don't seem to recongised the Octopus Agile tariff name - are you on an EV special instead ?

If not using an EV and EV tariff - we need to see if tariff type style beats single rate - and the peak and off peak register usage - prefereably annual - to advise.

akh43

LangleyAgent said:

It's a Worcester Greenstar 30CDi classic system

Is this not a combi boiler with no tank to store the hot water? Ie it heats the water as it comes through through the taps?  I am sure this is the boiler I have and that's how mine works.

FreeBear

akh43 said:

LangleyAgent said:

It's a Worcester Greenstar 30CDi classic system

Is this not a combi boiler with no tank to store the hot water? Ie it heats the water as it comes through through the taps?  I am sure this is the boiler I have and that's how mine works.

The Greenstar 30CDi was available in two flavours. A combi, and a system boiler. Looking at the specs on the 30CDi, maximum electrical consumption is quoted as ~150W, so pretty low. Even on a ToU tariff such as Octopus Agile, there is going to be negligible savings running the boiler at night instead of morning or early afternoon.

Just set the DHW timer to fire the boiler up ~30 minutes before you need it in the morning, and make sure the immersion heater is switched off at all times.

matelodave

The best time to heat your tank is just before you need to use it and then just heat as much as your require. The electricity consumption of a gas boiler is negligible compared with the amount of gas or leccy that other stuff consumes

We find that an hour or so before we get up gives us more than enough for our morning ablutions and sufficient hot water for the rest of the day until it reheats the next morning (we do have a 200l tank which can last us two days so a smaller one might not be sufficient) We've also found that heating the tank just once uses a lot less energy that doing it several times a day or leaving the hot water on as it avoids the heating unit cycling

If you need a bit more hot water for an evening bath or shower, then put it on for half an hour before, dont heat up the whole tank just to let it cool down overnight.

There's no advantage it keeping a hot tank hot all day or all night as a hot tank loses more heat the hotter you keep it.

Adjust your temp down to around 50 degrees (we get away with 45 degrees) and don't run off short lots of hot water  by rinsing stuff (including your hands) under the hot tap.

The amount of cold water you run off is equalled by the same amount of hot water sitting in the pipework to get cold until the next time and if you've got a combi then it goes flat out every time you turn on the hot tap.

Likewise minimise your use of hot water by having shorter showers rather than long baths and fit a low flow shower head. You can probably save nearly a tankful of hot water a day with a bit of thought on how you use (or waste) it.

born_again

akh43 said:

LangleyAgent said:

It's a Worcester Greenstar 30CDi classic system

Is this not a combi boiler with no tank to store the hot water? Ie it heats the water as it comes through through the taps?  I am sure this is the boiler I have and that's how mine works.

It would appear not.

But perhaps Op could confirm if they have a hot water tank.👍

https://www.wolseley.co.uk/wcsstore/ExtendedSitesCatalogAssetStore/images/products/AssetPush/DTP_AssetPushHighRes/std.lang.all/ti/on/Worcester_100947_Installation.pdf?srsltid=AfmBOorLC0E3W_kokiEjE0cICjuHhNr-YhR0CyIGn9Fft1MWRJ0YxDQI