Installing a programmer/timer for an unvented hot water cylinder with dual immersion heaters

[dg85]

I wasn't sure if this should go in this forum or in the electrical forum but hoping this is the right place.

I've got an OSO Direct 20 RD unvented water heater (210 ltrs nominal storage at 2 bars).
This is in a 2 bed flat, electricity only.

From reading around and looking at the manual I understand it has 2 immersion heaters. Both of which are wired to two physical switches on the adjacent wall.

I know nothing about these things so forgive any stupid questions, but my understanding/assumptions are that the heaters are permanently receiving power and supplying current to the elements when the internal thermostats drops beneath the temperature set by the adjustment screw (60°C for both).

This will obviously cost a lot of money, especially in today's energy climate. So i'm looking to reduce my outgoings by installing a programmer/timer (or two, one for each immersion heater?).

I believe the intent behind the two heater design is that the lower is fed with economy 7 electricity at night. I'm not on an economy 7 plan although we do have a smart meter which is compatible. I'd have to switch plans to take advantage of this though and that would involve exit fees and no doubt a higher tariff overall (currently fixed at 18.35p per kWh until Sept '22).

Questions:

1. Am I incorrect in my assumptions?
2. Would a timer help reduce costs?
3. What is the difference between a timer and a programmer? Which would be suitable?
4. Would I require a separate timer to ensure the lower heater turned on at night and the upper in the morning (assuming some future move to an E7 plan)?
5. Are timers simply wired in-line i.e. would I have to cut the cable and wire the timer up in the middle?)
6. Can anyone recommend a timer/programmer?
7. I understand some timers have a boost function, our shower is non-electric so i'm assuming we'd want this available on whichever timer (assuming two separate units) to the lower immersion heater. Is that correct?

Many thanks. As mentioned, this is far outside my comfort zone but seeking to learn more so any advice is greatly appreciated.

 

[BlueLoo]

Some thoughts:

My understanding is that the top heater is for sink only loading and the bottom for bath loads (hence you have immersion switches with on/off/sink/bath).

Because you don't have indirect (boiler) heating, i might suggest you just leave the top heater on for normal daily use and only use the bottom one when having a bath.

That being the case. You can get timer immersion boost switches which boost for 15,30, 60,120 mins etc
I have one of these on my HW tank because i only use the immersion as a boost heater for baths and I'm forever forgetting to turn it off.

But. If you want to have a timer approach to the sink only heater (or both) they are cheap and easy to fit.

I wouldn't bother for the reason of lack of indirect heating but ymmv obv.

Wouldn't bother with a night time tarrif unless you do a gross usage calc and see if any savings you make on night time usage justify the more expensive service charge.

 

[lloyda]

I believe the intent behind the two heater design is that the lower is fed with economy 7 electricity at night.

Spot on. Heat the entire tank on economy 7, and only top up on day rate if you need to.

If you are not on E7, and you don't have gas, how are you heating the flat?

 

[Madrab]

Am I incorrect in my assumptions?

Nope, that's how it would usually work

Would a timer help reduce costs?

Yes, as it would only heat when you require it but it wouldn't be as much as you think as the water would be colder and require more energy to heat up properly each time

What is the difference between a timer and a programmer? Which would be suitable?

A timer is a manual device that needs you to switch it on for it's set time periods, a programmer allows you to set times and will work autonomously once set

Would I require a separate timer to ensure the lower heater turned on at night and the upper in the morning (assuming some future move to an E7 plan)?

E7 meters have dual readings and usually switch over automatically at certain times of the day to low cost energy. So whatever leccy is used at off peak would be at the lower rate

Are timers simply wired in-line i.e. would I have to cut the cable and wire the timer up in the middle?

Timers can usually just replace the current switches and use the same cabling and back box

Can anyone recommend a timer/programmer?

Horstmann are usually pretty good for both

I understand some timers have a boost function, our shower is non-electric so i'm assuming we'd want this available on whichever timer (assuming two separate units) to the lower immersion heater. Is that correct?

The boost functions are usually used for the top immersion element to allow a quick heat up for the top 1/3rd of the cylinder, for say basin washing, dishes etc. If you want enough water to supply a good shower then boosting the bottom element may help and no reason you couldn't have one but ideally the bottom element would be timed to heat overnight and heat up the whole cylinder.

 

[Harry Bloomfield]

Spot on. Heat the entire tank on economy 7, and only top up on day rate if you need to.

If you are not on E7, and you don't have gas, how are you heating the flat?

It's not as simple as just getting E7 set up, it needs to be worth your while to have E7 - you need to be able to make enough of your consumption during those 7 hours, to off set the cost. E7 rate is much cheaper, but the normal day rate consumption cost becomes higher.

 

[lloyda]

Hence my question about how the flat was heated. It would not be the first time that storage heaters were in use but not on E7.

 

[Harry Bloomfield]

Hence my question about how the flat was heated. It would not be the first time that storage heaters were in use but not on E7.

I fully agree, I was just pointing out that the E7 needed to be economically worthwhile.

 

[oldbutnotdead]

Is this, by any chance, a rented flat? (Electric only heating is a favourite for landlords-low install and maintenance costs, high operating costs). If it is rented you shouldn't be doing anything that requires a screwdriver- fixed installation is landlords responsibility.
With a modern cylinder and no split tarriff, your savings by installing timers will be fairly small. Experiment for you- leave both heaters on for long enough to heat the entire cylinder to setpoint Read your electricity meter, leave both heaters switched on for a week, read meter at the end of the week then the next week switch both heaters off, only switch them on when you plan to use hot water. Read meter at the end of the week, compare numbers.
This assumes other electrical use is consistent from week to week and may not give useful data if your space heating is electric as well...

 

[JohnD]

This will obviously cost a lot of money, especially in today's energy climate.

This may perhaps betray an incorrect assumption.

A modern unvented cylinder is insulated to a very high standard

The elements will not be running continually unless you leave a hot tap running 24 hours a day. Once the cylinder is hot, very little heat escapes through the insulation.

If you run a 90 litre bath, an element will run for about an hour and a half to replenish the hot water you have used, and will then turn off.

Some people think it only takes 20 or 30 minutes, but this is incorrect, unless the cylinder is already partially hot.

Some people think an element uses power all the time it is switched on, and this is also incorrect.

If you never have hot baths, and do not have E7, you may have no benefit from the lower element.

And if you do not have E7, the cost of a timer may be money down the drain.

 

[Harry Bloomfield]

The elements will not be running continually unless you leave a hot tap running 24 hours a day. Once the cylinder is hot, very little heat escapes through the insulation.

If you run a 90 litre bath, an element will run for about an hour and a half to replenish the hot water you have used, and will then turn off.

Some people think it only takes 20 or 30 minutes, but this is incorrect, unless the cylinder is already partially hot.

Some people think an element uses power all the time it is switched on, and this is also incorrect.

A reasonable compromise might be to leave the upper element on all of the time, which would ensure there is a near constant supply for getting washed and washing up, but only have the lower element turned on manually when a bath is intended. If E7 is available, then it is worth ensuring the lower element is on a timer and set to always come on during E7 times each night.