Most efficient way of heating water

misterjingles

In light of the current energy price hikes , I'd just like to verify that I'm getting the best out of my gas units.

We keep our hot water on "constant" via our controller unit. i.e it doesn't click on & off twice a day in winter like our heating circuit.

We do this because I'm sure I was once told that it cost more to let the tank cool down & re heat rather than keep it up to temperature all the time.

Any heating gurus out there care to confirm this - or is it an urban myth ??

space_rider

In view of the increases I am trying to reduce what I use. I live in a 2 and a half year old semi with a condensing boiler. Before BG put their prices up my hot water was on twice a day for an hour each time. Water was always hot and never ran cold. Yesterday I switched it to just once a day and its been hot enough for 4 showers, which is fed from the gas heated hot water, I have washed up though I do have a dishwasher and when I checked half hour or so I had used 1 unit instead of 2 and the water is still hot enough for another shower. My thermostat is set to 60. I don`t have a long shower as I have a hot water but can`t say how long my teenage daughters stand under it for!

Cardew

misterjingles wrote: »

We do this because I'm sure I was once told that it cost more to let the tank cool down & re heat rather than keep it up to temperature all the time.

Any heating gurus out there care to confirm this - or is it an urban myth ??

This comes up time and time again and is, as you speculate, an urban myth.

To illustrate, the best analogy would be to consider your kettle. Would you keep that boiling all day(leaving aside the water evaporation)? It is exactly the same principle.

That said, a well lagged water tank loses surprising little heat - the equiv of 2 to 3 kWh every 24 hours.

There is also some heat loss from the pipes from boiler to tank.

Even if you had your water on timed, there would normally be some hot water left in the tank so you would still get a little heat loss.

Bear in mind also that heat 'lost' from the tank, still warms the house; so for the majority of the year it is just another form of heating; which is why most tanks are in an airing cupboard.

Although timed heating is clearly cheaper than leaving it on 24/7, the actual extra cost for the latter is not as high as some people believe.

misterjingles

Cardew wrote: »

This comes up time and time again and is, as you speculate, an urban myth.

To illustrate, the best analogy would be to consider your kettle. Would you keep that boiling all day(leaving aside the water evaporation)? It is exactly the same principle.

That said, a well lagged water tank loses surprising little heat - the equiv of 2 to 3 kWh every 24 hours.

There is also some heat loss from the pipes from boiler to tank.

Even if you had your water on timed, there would normally be some hot water left in the tank so you would still get a little heat loss.

Bear in mind also that heat 'lost' from the tank, still warms the house; so for the majority of the year it is just another form of heating; which is why most tanks are in an airing cupboard.

Although timed heating is clearly cheaper than leaving it on 24/7, the actual extra cost for the latter is not as high as some people believe.

Thanks for the advice ... Typically( in winter) we would have our heating set to click on twice during any 24 hr period. This would be say 6.30 am to 8.30 am in the morning - to warm the place up prior to breakfast, and 4.30 till 11pm . If the Hot water timings followed suit, do you anticipate that we could cover hot water demand during the day for say , washing up & cleaning purposes..( we wouldn't be running any hot baths ) & would we save anything substantial.

Cardew

Heating the HW for 2 hours in the morning would mean that you have a full tank of water - in fact the boiler would not be heating for anything like that period.

In theory the most economical way would be to have the heater on and off for a period BEFORE you start using it for washing in the morning.

The only way is to experiment with timings and your pattern of use.

As for savings? Depends how you define substantial; probably a lot less than most people envisage.

De1b0y

Hi.
I am new to this forum.
I have E7 electricity. My current practice is to leave E7 heating water all night (large tall tank with two elements) and boost with Gas indirect heating of the tank water early evening (this is on a timer).
I could quite easily heat the water overnight using Gas instead of E7. What is the current thought on this?
Also, as we have both E7 and Gas options our home heating system has evolved in a rather odd way. Semi-detached property with Gas central heating downstairs and E7 night storage heating upstairs for background heating. How 'bad' are storage heaters; should I consider removing them and extending my central heating?
Many thanks
De1b0y

Cardew

De1b0y wrote: »

Hi.
I am new to this forum.
I have E7 electricity. My current practice is to leave E7 heating water all night (large tall tank with two elements) and boost with Gas indirect heating of the tank water early evening (this is on a timer).
I could quite easily heat the water overnight using Gas instead of E7. What is the current thought on this?
Also, as we have both E7 and Gas options our home heating system has evolved in a rather odd way. Semi-detached property with Gas central heating downstairs and E7 night storage heating upstairs for background heating. How 'bad' are storage heaters; should I consider removing them and extending my central heating?
Many thanks
De1b0y

The efficiency of your gas boiler determines if gas is cheaper than E7 to heat your water.

Gas boiler efficiency can be anything between 50% for a really old boiler(few are that bad) to 90%+ for modern condensing boilers

If you pay, say, 3p/kWh for your gas and your boiler is, say, 75% efficient then you will effectively be paying 4p/kWh - which you can compare with the cost of E7.

However you do realise that on an E7 tariff you pay quite a bit extra for your other 17 hours electricity??? - compared to a 'normal' tariff.

You should consider extending your gas CH to upstairs, but there are a number of factors that will affect your decision. Not least what will be the future trend on gas v electricity prices.

tomstickland

misterjingles wrote: »

We do this because I'm sure I was once told that it cost more to let the tank cool down & re heat rather than keep it up to temperature all the time.

That's an urban myth.
There is heat flow from tank whenever it is hotter than the surrounding air/building structure. The higher the temperature difference then the higher the rate of loss. If you keep your tank at temperature at all times then there will be more heat passed to the surrounds compared with allowing it cool when not in use.

As Cardew says, there's 3-4 units of loss per day from a well insulated storage tank. I actually verified this by comparing daily usage of electricity from before and after a period where I decommissioned my hot water system.

In my case it's cheaper to heat overnight on E7 and use the hotwater the next day. Only just cheaper though.