Efficient programme for water heater

Colely

Novice Member
Hi everyone,

I’ve just moved into a 1 bed flat and everything is electric - just got our first electric bill through and it was £145!! I think the culprit may be the water heater which we currently have on all night. It is a OSO Super S unvented hot water cylinder controlled by a Horstmann Elctronic 7. We are not on E7 so what is best programme to have it on? We only really need some hot water in morning and evening as both work full time.

Thank you
 

IronGiant

Moderator
Depending on what time you get up and off for work I'd do 6-9:00 in the morning and the same in the evening.
 

ufo550

Well-known Member
I would see if you could obtain an Econmy 7 tariff, to heat your hot water on the cheaper rate overnight. That’s what that programmer has been design for.

Do you have a new build property, or have you taken over occupancy from someone else? All electric properties are costly for fuel, and require very good insulation etc.

What electric heating do you have?
 

Hixs

Distinguished Member
Assuming that is for a month? because if it's 3 months, then that doesn't seem bad for an all electric gaff.

We're €125/month over winter and most appliances run off gas.
 

stiv674

Well-known Member
It would also depend on how well insulated the cylinder is, a new one will keep water hot enough all day so you'd only need it on in the morning for a couple of hours.

An older inefficient one might need an hour and half or so twice a day.
 

MrFraggle

Distinguished Member
You certainly want the water always to be warm as heating very cold water during the winter months will really cost. Your thermostat should keep it at whatever temp you have decided on and only use a but of electricity when it drops below that temp ir you use some.
 

IronGiant

Moderator
a new one will keep water hot enough all day so you'd only need it on in the morning for a couple of hours.
Not if they both have a shower before heading for work :) Unless it reheats it in those couple of hours. As Mr F says, with a modern well insulated cylinder, the electrics will only really heat it as it is used. I'd check out E7 rates as ufo suggested.
 

stiv674

Well-known Member
Not if they both have a shower before heading for work :) Unless it reheats it in those couple of hours. As Mr F says, with a modern well insulated cylinder, the electrics will only really heat it as it is used. I'd check out E7 rates as ufo suggested.
Well yeah it would depend on when most hot water is used, I shower in the evening so based it on that :)
 

ufo550

Well-known Member
Even the most modern insulated will dissipate temperature after a few hours. I know that, because my gas boiler comes in the morning to heat the water in the tank, even though its had no use overnight. :)

Another common myth having your hot water heated 24hrs a day; you should only heat it, for when you need it. You wouldn't keep your kettle boiling all day, for when you need hot water for a cuppa.
 

KyleS1

Distinguished Member
For a family of four, I run the hot water for 1 hour in the morning, 30 mins at lunch and one hour in the evening. I’ve got a crap inefficient cylinder too. That’s through gas so not sure on how long it takes with electric only.
 

IronGiant

Moderator
You wouldn't keep your kettle boiling all day, for when you need hot water for a cuppa.
My late grandma's hot water cylinder didn't have a thermostat. There was a switch in the living room and if anyone wanted a bath it was turned on until you could hear it boiling in the bathroom upstairs :eek:. Fortunately modern electric hot water cylinders do have one :)
 

DPinBucks

Distinguished Member
Even the most modern insulated will dissipate temperature after a few hours. I know that, because my gas boiler comes in the morning to heat the water in the tank, even though its had no use overnight. :)

Another common myth having your hot water heated 24hrs a day; you should only heat it, for when you need it. You wouldn't keep your kettle boiling all day, for when you need hot water for a cuppa.
Agreed.

There is no point using power to keep water warm all night when you only need it first thing.

Ideally, you should switch it ON in the morning or evening so that it is at just the right temperature at the moment you first want to use it. Similarly, switch it OFF so that it is still usable at the time you last need it.

I don't know your routine, but I would suggest say start with ON-periods of 06:30-08:30 and 16:30-21:30, and adjust as necessary with experience.

Similarly with heating, if that's also water-based and you have separate controls.
 

IronGiant

Moderator
I'd be interested to know how much you save by letting it cool a bit between the windows of planned usage over maintaining it at say 65 deg permanently. You still have to heat it back up again twice a day.
 

IronGiant

Moderator
I wouldn't and didn't... I'm just curious how much more it costs to keep it "simmering" :D at 60 over keeping it "lukewarm" at 50 (assuming it ever drops that low if you are heating it twice a day anyway).

Note: I'm only thinking of electric heating where there are no "losses" out side of the cylinder. Clearly running your gas boiler all day just to keep the hot water piping hot is extremely inefficient.
 

IronGiant

Moderator
Doing that 24/7 would use more energy that at set times.
Of course, that's not an issue. Just how much more is what I'm wondering.

I've seen anecdotal evidence that keeping your gas boiler on 24/7 in the summer costs 25% more than using it on a timer. I suspect with an electric element the % difference will be lower, but,of course, the difference in cost per kWh may be more relevant than any efficiency differences.

Edit: Regardless, I recommended a time schedule in post #2 because it will clearly save them some money. I just don't want them to think their water heating bill will reduce by 75% by only having the water on 6/24.
 
Last edited:

DPinBucks

Distinguished Member
Of course, that's not an issue. Just how much more is what I'm wondering.

I've seen anecdotal evidence that keeping your gas boiler on 24/7 in the summer costs 25% more than using it on a timer. I suspect with an electric element the % difference will be lower, but,of course, the difference in cost per kWh may be more relevant than any efficiency differences.

Edit: Regardless, I recommended a time schedule in post #2 because it will clearly save them some money. I just don't want them to think their water heating bill will reduce by 75% by only having the water on 6/24.
OK, you asked for it, but we'll have to delve into basic thermodynamics to set the scene, and even then there are too many variables to calculate properly.

A tank of hot water will lose heat at a rate determined by its insulation properties and the difference between the water temperature and the outside air. So it will cool from 60 to 59deg slightly faster than from 59 to 58. When it reaches the air temperature, it will stop cooling at all.

So, in reverse, to heat it back from 59deg to 60 will use more power (ie take longer) than from 58 to 59, because it's losing heat faster. The difference is tiny, but it's there. The effect is that it takes a little bit more power to maintain the water at 60deg than to let it cool to 50 then heat it back to 60. In a well-insulated tank, it might take a few hours to cool to 50, but only a few minutes to heat it back to 60. Compare that with maintaining it a 60 throughout. Without knowing all the relevant factors, especially the efficiency of the insulation, the thermal mass of the towels in the airing cupboard and whether you open the door to take the vacuum cleaner out, we can't estimate how much would be saved, but even though it's small, it's not zero.

The more the water cools overnight, the greater the savings. If it actually gets to near the air temperature, so that it stops cooling significantly, then the savings can be much larger. Suppose it stays cool like that for two hours. Then it's not losing any more heat, but if you'd kept it hot you'd have wasted two hours'-worth of heating power.

As you point out, gas and electrical power are different. With electrical heating - no power wastage and instant on/off - it's always better to switch it off overnight, using experience to judge the timing. Any saving, no matter how small, must be worth having.

With gas, it depends on the efficiency of the insulation. With the 60->50deg scenario, it might be worth leaving it on, though I wouldn't personally. If it cools more than that, it should be switched off overnight. You should always switch off space heating overnight.

Hope this is what you wanted.
 
Last edited:

IronGiant

Moderator
No, I'm very disappointed, you completely left out the thermal mass of the towels in the airing cupboard and whether you open the door to take the vacuum cleaner out. :laugh:

Seriously though, nice summary :) :thumbsup:.
 
Last edited:

DPinBucks

Distinguished Member
No, I'm very disappointed, you completely left out the thermal mass of the towels in the airing cupboard and whether you open the door to take the vacuum cleaner out. :laugh:

Seriously though, nice summary :) :thumbsup:.
Thanks. I've edited the original in the light of your comments. :D
 

IronGiant

Moderator
Brilliant, good work... :laugh:

Edit: somewhat off topic but my new condensing combi boiler has a keep warm feature for the hot water. It can keep the hot water heater matrix warm for faster hot water. It has 3 settings: On, Off and Eco. Eco "learns your usage" and only keeps it warm at times that you generally use hot water. As you can figure out, the real Eco setting is "Off". :laugh:
 
Last edited:

The latest video from AVForums

The Best Movies and TV Shows Coming to Netflix in November 2020: Tom's Thumbs.

Latest News

Tom's Thumbs: What is coming to Netflix in November 2020
  • By AVForums
  • Published
Melco anniversary edition N10 library announced
  • By Andy Bassett
  • Published
What's new on Disney+ UK for November 2020
  • By Andy Bassett
  • Published
Denon, Marantz and Yamaha AV receivers hit by HDMI 2.1 bug
  • By Andy Bassett
  • Published
McIntosh launches MX100 AV processor and MI347 power amp
  • By Andy Bassett
  • Published
Top Bottom