Storage heater wiring

3 Feb 2014
Reaction score
United Kingdom
I have to replace a couple of storage heaters in my house. I get a 14 hour cheap rate tariff (called Option 14, unsurprisingly), so I get 14 hours of cheap rate electricity every day :). The old heaters were designed for economy 7 (7 hours of cheap rate power daily) so they were fitted with half rated elements to work with my tariff.
I can't find any new heaters that come with these half rated elements, or any replacement elements of this type now. So my question is this: is it OK to fit standard storage heaters on my 14 hour a day tariff? I can't see why not, since the heaters are thermostatically controlled anyway so surely they would just shut off when charged fully? But I'm not an electrician and I'd prefer not to set fire to the house.
Sponsored Links
You are correct in your assumptions, the heaters are thermostatically controlled so will stop charging when they get to heat.
They will, of course, start charging again if some of the heat dissipates.
Sponsored Links
I think it means that because the OP has fourteen hours cheap rate (instead of the usual seven) they fit heaters with half the normal consumption thus not giving you twice as much cheap electricity.

They aren't silly.
They are (apparently) half rated, they look like normal elements but I remember having to take the original elements back to the supplier and they gave me the half rated ones in exchange. Never really understood why they were necessary though.
Ah, so keeping full rated elements would give the heaters twice the effective heat capacity in the right circumstances. Might be worth changing the elements then, get more charge in the heaters during the day.
If your heater can heat up in 7 hours it will use far more current then heating up in 14 hours and if the supply is designed for 14 hours using the heaters designed for 7 could overload your system. Without knowing the design we just don't know if you do or don't have enough power.

So if all heaters at 1.5kW and you have 7 then that's a 45A load on switch on, but with 3kW it's 90A load on switch on we simply don't know if you can or can't draw 90A.
I wasn't really thinking about the total load, but that's a really good point. I've done a few calculations and if I just replace the 2 heaters I'll be drawing 6.2KW in total for heating, 27A, and the main fuse is 100A so I guess that will be OK. There's not a huge amount of additional load. Changing all the other elements would add another 2.8KW, 12A, but I think I'll just leave the other heaters alone. Thanks.
It doesnt matter what size the main fuse is, it matters what size circuit breaker/fuse you have in your board and what size cables they're fed by and if they're on individual circuits or not
All the breakers are 16A, and it looks like all the wiring is 2.5mm T/E, one cable to each heater. The heaters I am replacing were drawing 1.2KW, but I'm changing them for 2 element heaters, so they will be 1.7KW each. Can't see a problem with this.
No, probably wouldn't be a problem - even from the supplier's point of view.

Storage heaters are 'normally' 3.4kW so you would still be on 'half rated'.
Last edited:
It means you don't get to use any more cheap electricity in the fourteen hours than you would in seven.
Ignoring interim losses, you can't anyway. A heater which stores XkWh will store that much whether you fill it up over 14 hours or 7.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links