On Feb 20, 1:28*pm, JimK wrote:
at what point does it start to make sense to be on Economy 7 leccy?

Generally the answer is...
- Do the thermal loss calculations
- Do the capital install & depreciation cost for GCH
- Do the capital install & depreciation cost for E7

The reality is...
- You need insulation levels to current standards
- You are at home all day (work from home or retired)
- You have a flat or bungalow
- You do not have gas available
- You do not want the disruption of GCH re solid floors

The killer for electric heating is any peak-rate requirement :-)

E7-only storage heaters (Automatic):
- Insulation - CWI & Lost Insulation essential
- Size critical - otherwise cold at night
- Reliable - 25yr without maintenance
- Low Depreciation - £10/yr typically
- No Servicing - £0/yr
- Ugly - fronts should be "pressed" to look like a radiator, bring
back the old folded punched aluminium grills
- Overall - risk of too hot overnight as they "leak" 60% (3 Tog duvet)

E7+Peak storage heater (Duoheat):
- As above
- Reliable - risk of 5-10yr due to electronics & thin film front
elements
- Depreciation - risk of 3-5x higher
- No Servicing - £0/yr
- Overall - less risk of too hot overnight as they reduce E7 charge by
using more peak charge

Consider an automatic E7 heater plus separate panel heater is just the
same as a Duoheat either without the cost or potentially the same 25yr
no-failure reliability of the capillary automatic type.

E7 fan storage heater (Commercial):
- Actually the only type that really work
- Costly - £700 for 24kWhr, £950 for 40kWhr and a stupendous £1300 for
48kwhr storage
- Size - 285mm depth is really big
- Wall thermostat or programmer - turns on fan to pull heat out
- No cook overnight - you get heat when you want it

Examples are Creda TSR, Dimplex VFMi, Elnur do a cheaper one without
peak-rate boost element.
The fan outlet is at the bottom, they hold heat for 3 days, heating on
demand.
So you would say set a 15oC background temperature, then boost to
16-18-20oC by manual push-button or programmer or occupancy sensor.
Germany does a lot of fan storage heaters, lots of variations.

The problem remains even with GCH that there is no (true) radiant
source.
It is worth considering that when looking at alternatives, it's not
just the visual focal point but the radiant heating.
21oC in a room with fan heaters is pretty miserable even whilst warm,
19.5oC with a radiant heater is better (not the halogen rubbish, I
mean a proper radiant type like Tansun - not practical indoors).

The future will eventually be electric heat pumps with CO2 compressors
(twin scroll, DC invertor, continually varying output vs cycling).
They will be 9-14kW output feeding a large thermal store. Potentially
used in series to boost output temperature - existing R410A heat pumps
suffer due to low CoP at low temperature and so really need underfloor
heating re 45oC output or two heatpumps in series for conventional
undersized radiators. There will still need to be a boost on cold days
unless CO2 heatpump (they go to CoP parity only at -25oC), that could
be handled by E7 element with some peak usage.

E7 is good for hallways with leakage into bedrooms, in an otherwise
well insulated house.
E7 in a living area really needs a balance of E7 combined with peak,
Duoheat has breakdown risk & cost, conventional Automatic have ugly
aesthetics but reliability and ease of adding another heater. Size
correctly E7 NSH work ok, just not brilliantly. The only systems that
really work are the big commercial units - but their depth is an
issue. Germany "fits them in many packages" and variations re leakage
levels. A widespread E10 system would work well - that requires nukes
because the windmill crowd just can't create the kW required for an
entire country (nor could the distribution system handle it). We are
adding future cost to the grid, without considering how to pay for it.
Nukes are the only practical solution.