Electric only flat and underfloor heating

nameloc2080

I recently moved into an electric only flat and I need some advice. I’m on economy 10. I have two meters (each with its own MPAN): one providing electricity at the day rate and a second providing off peak electricity only at set times. The only thing using the off peak supply is the electric underfloor heating which is in all rooms and hardwired to the fuse box. 

At the moment I find it can get cold in the winter when the off peak power is off and therefore no underfloor heating. The underfloor heating has no time controls and only comes on during off peak hours with manual thermostats. If I turn the heating off in a room before I go to bed by the time I get up and turn it back on I then have to wait for the next off peak time to start.  So last winter I was heating up empty rooms overnight to make sure they were warm for the next day.

I’m not sure if the electric underfloor heating is ideal on this set up as I understand that it is most efficient to maintain a temperature rather than switching on and off like this.

Between October and the end of May I used 4525 KW on the off peak supply all on underfloor heating. 

I’m looking to see what I can do to run the electric underfloor heating more efficiently. To mix things up I currently have an electric immersion heater which is on/off only and is connected to the standard supply (not the off peak). I manually switch this on normally once a day for 30 mins. I may replace this with an instand water heater as only 2 sink taps but in the meantime I'm looking at getting at least a timer.

Option 1:

Keep it as it is. The off peak supply operates all days 0000-0700, 1330-1630, 2300-2400. No on peak supply to the underfloor heating. I did ask an electrician if I could also connect the underfloor heating to use the standard always on supply when off peak finished, using some sort of controller but was told it was not possible with my hardwired fuse box setup. This would be at 14.02p per kWh (the off-peak rate).

Option 2:

I spoke to an electrician who said they could move the hardwired electric underfloor heating off the timed off peak supply to the always on supply. I would then pay the standard rate at all times. This would be at 25.76p per kWh.

Option 3:

My supplier Octopus said I could switch to economy 7 on a single smart meter, replacing the current two meters. I would lose the off peak hours I currently get in the day as economy 7 is off-peak overnight only. The daytime rate would be higher than I currently have (25.76p per kWh) as one of the benefits of my setup is that because my off peak supply is cut in on peak hours I don’t pay the higher daytime rate on that meter. The other (the always on meter) is at the standard non E7 rate. Night rate 14.02p per kWh and day rate 32.18p per kWh.

I’d appreciate any input please. Thank you.

QrizB

Your heating system is intended to be run with the underfloor heating always on, heating overnight and using the thermal mass of the floor slab as a heat store to even things out. If you're switching it off overnight you're missing out on 7/10ths of your cheap rate heating hours and it's not surprising that your flat gets cold.

Your immersion heater should also be connected to the cheap-rate supply.

Some time in the next couple of years your current meters will be replaced, almost certainly with a single smart meter. You might lose Economy 10 at that time. Do you own your flat, or rent?

Re Option 1, this is probably your best bet for now. You've got a pretty good tariff setup (because Octopus don't really support Economy 10) where you get 10 hours (not 7) at their E7 off-peak rate but your day-rate meter is on their single-rate tariff.

Option 2 will increase your heating costs since you'll be paying 25p/kWh not 14p.

Option 3 is only worth going for if you're prepared to spend £2-3k on having storage heaters installed. If you own the flat, this might be worth doing. If you rent, it's a question for your landlord.

nameloc2080

QrizB said:

Your heating system is intended to be run with the underfloor heating always on, heating overnight and using the thermal mass of the floor slab as a heat store to even things out. If you're switching it off overnight you're missing out on 7/10ths of your cheap rate heating hours and it's not surprising that your flat gets cold.

Your immersion heater should also be connected to the cheap-rate supply.

Some time in the next couple of years your current meters will be replaced, almost certainly with a single smart meter. You might lose Economy 10 at that time. Do you own your flat, or rent?

Re Option 1, this is probably your best bet for now. You've got a pretty good tariff setup (because Octopus don't really support Economy 10) where you get 10 hours (not 7) at their E7 off-peak rate but your day-rate meter is on their single-rate tariff.

Option 2 will increase your heating costs since you'll be paying 25p/kWh not 14p.

Option 3 is only worth going for if you're prepared to spend £2-3k on having storage heaters installed. If you own the flat, this might be worth doing. If you rent, it's a question for your landlord.

Thanks for your reply. I own the flat in question. I will consider storage heaters in the next few years as I guess these will be more efficient than 45 year old underfloor heating. I ran the underfloor heating overnight last winter but still found it cold sometimes outside of off peak hours. I may just use my portable oil plug in heater to top up heat as required when this happens.

I've been leaning to Option 1 for now because it has the lowest kWh rate for day and night. If I keep the current set up I will certainly put the immersion heater on the off peak supply.

Scot_39

Underfloor heating only works on restricted supply if it has enough thermal "mass" - i.e. stored heat capacity - to last all day between charges and can actually take that amount of charge (time window x rated power constraint).

Or in your case on E10 all morning to afternoon boost - and then all evening from that boost to 11pm charge.

Cutting it off for 7 of your 10 hours if E10 - or is it 8 of 11 given your quoted times (00:00->0700=7 +13:30-16:30=3 +23:00-24:00=1 == 11) - probably greatly reduces the amount of heat stored - so then available - hardly surprisingly limits power use / cost but also heat output leaving you cold. 

(Floor might not always charge for full 7 or 8 hrs overnight anyway based on internal or room thermostats - my NSH seldom charge anywhere near my full 10 hours off peak on E10 - my case split 3 ways - 5 overnight - 3 afternoon and 2 evening - but I run them on low input and run low room temps cf many).  

Their is also a small risk that 7 hours just wouldn't be enough on coldest days - my former next door neighbours replaced 3 old lossy NSH on E10 - with 4 HHR - so increased overall charge powers by c30% - to cope with their 21C desired temps and reduced 7 hours E7 charging)

But before going expensive

Could it be worth trying simple programmable thermostats - to automatically switch back on (or set a low base temp overnight - then increase for only the last n hours) - before the 7am GMT / 8am DST cut off - might be a simple - and not to expensive - interim solution for you to try get a better balance of charge time, cost and available heat at desired times.  Especially if at home all day.

 

However

4500 kWh just on heating though does seem a lot - especially for a 1 bed flat. And you say even if left on - your still cold in mid winter.  So do maybe worry - whether its really heating the space effectively - or dare I say it - leaking quite a bit of heat out in losses. 

Do you run quite high room temperatures ?

What sort of floor coverings are in place ?

[You could even try having a go at say the Dimplex ratings calculator - it asks some non technical questions about sizes, room and windows, external walls etc 

https://www.dimplex.co.uk/room-heating-calculator

It's very much a "near worst case winter" energy number - e.g. 21C inside / -3C outside defaults iirc for an English living room (suggests use -5C in Scotland iirc) - as its a sizing tool so heaters cope with that case - so dont worry that it means thats a normal average daily consumption estimate. 

But it might be interesting to see what it expects worst case vs your 4500 number over the n months of winter in use for - across your room / window sizes - or taking your highest winter bill / 30 or 31 etc.

Note If you select a normal panel type heater - it is simple rated power - if you select NSH - it reflects the charge stored - over by default 7 hours iirc]

Future - as your supplier - just a warning - any new meter likely to behave differently form your twin

Because I suspect your on an independent 2 meter set-up - day/night? and restricted heat only rates - your probably going to be upgraded to single meter smart pretty soon (even if its not an RTS set-up) - which will almost inevitably mean everything will go peak / off peak rate purely by time - on all circuits.

(Some suppliers used to upgrade to two independent digital to replicate - using one purely for the restricted - but dont remember ever having seen any evidence here any do that with smart meters)

Most standard smart meters cannot replicate a 2 independent meter system - but some manufacturers do make those that do - as most cannot record your 24.7 and your restricted energy use separately - only the total current - so power/energy flow to both.

So if a meter change is imminent I wouldn't necessarily spend money now getting an electrician moving say the HW to off peak consumer unit.

You might want to check for anymeter certification or install dates.

(Frankly give the emails others with legacy or even older generation multirate digital meters have had - surprised you havent been caught up in the RTS switch off mail shots)

Ectophile

I would stick with Option 1 for now.  In cold weather, turn the thermostat to a comfortable temperature, turn the heating on, then leave it alone to do its thing.

Option 2 will be frighteningly expensive.  Running your heating at 25p/unit for hours on end will cost a fortune.

4525kWh at 25p is around £1130.

Option 3 offers little advantage for you, compared with Option 1.  You will only have 7 hours of heating, and only in the middle of the night.  You will be even colder during the day.

In the longer term, modern high heat retention storage heaters can work well on E7, and you can wire the hot water into the E7 supply too.

Scot_39

Re the 10 vs 11 issue - I just read in another thread - apparently EDF did an economy 11 vairant with an 8 overnight + 3 afternoon split tariff at one time.