E7 Storage Heaters & E7 Water Heating - General Information Overload

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Night Storage Radiators

Comprise of a combination of both a storage component and a direct acting component, with the storage heating forming the base load and direct acting heating forming the 'boost' requirement. As a general rule all rooms must be well insulated for night store systems to work reasonably well. In 2012 building regulations terms homes must be built to very high standards of insulation in order to satisfy a storage heater system with radiant panels built in and which are controlled as a single unit, providing both off-peak and on-peak heating, controlled as a single unit designed to use at least 80% of the heating energy at the off-peak rate and no more then 20% at the on-peak rate, many uber homes are designed so that storage based systems provide between 80 and 100% of the room heating requirements for any given season. Most of the UK domestic property has insulation values considerably lower that new builds, so that design % is never achieved in older homes.

For the majority here without the 2012 insulating standards its quite a different calculation, for example old buildings were designed to leak, indeed both coal fires and coal range ovens would kill the occupants if the house was anything like airtight, the best you would hope for would be that the fire would go out before all the oxygen was burned off and the occupants died. Fast forward to now and the cellars have been filled in the 'coal hole' has long disappeared, gas lamps and coal fired systems are but a memory but the legacy of those years is that many people with chimneys also have storage heating systems when in fact they should never have been installed. A chimney with an effective restrictor where no outside air vents into the room would lose 1kWh per 24 hours of heat, however a chimney without an effective restrictor where outside air does vent into the room would lose 8kWh per 24 hours of heat. A typical system comprises storage heaters in the living room, hall, kitchen and would be unnesessary in the bedroom. The living room should supply 95% of the seasons requirement, the hall hall provides any heat required there, plus a general background level of heating in the upstairs [warm air drift] rooms.

Bedrooms are occupied primarily at night, so direct acting heating is generally much more appropriate, here 95% of the heating should be 'on peak' rates. I often 'bleat' about combination storage heaters which incorporate a direct acting convector heater for the living room so, if panel heaters are used as the supplementary heat source, a saving can be made on wall space. A further alternative, particularly if the dwelling is unoccupied during the day, is a fan storage heater. Storage fan heaters lose approximately 50% of their heat through their casing and the remaining 50% is available on demand through the use of the fan, which can be timed, or switched, to suit the householders requirement. Usually heaters would be positioned at the point of greatest heat loss [like an air curtain in a shop], generally under the windows. However in today's well insulated dwellings it is far less critical, heaters can be placed away from windows and the inconvenience of restrictions caused by curtaining, they are then best sited on an internal wall where the wall itself [breeze block & plasterboard] will become a heat retaining structure

Night-Time Water Heating

Not all electricity suppliers offer tariff's that suit the delivery of cheap[er] off peak electricity during the night, those that do, all offer an E7 tariff but only a few offer an E10 tariff. The difference between E7 and E10 is simply that E7 gives a total of 7 straight hours overnight only. E10 gives two lots variable, sometimes 5 during the night and 5 during the day, others 7 during the night & 3 during the day. E10 is the more expensive luxury end of E7 as it offers a top up of both your heaters and you water during the day-time. A water cylinder should always have two factory fitted heating elements, one at the top and the other at the bottom of the cylinder. Each individual heating element must be separately thermostatically controlled, the spec on the lower element must be capable of heating at least 85% of the cylinder contents and the upper heating element has to be capable of heating at least 60 litres of water. The lower element is connected to the off-peak electricity supply and the upper element to the on-peak for boost operation.

Each immersion heater has its own thermostat. The top heater is used for a boost if the off-peak night-time heated water has been used up, this top element is generally set at 60ºC, whilst the lower heater, used for heating the whole cylinder at the off-peak rate, is set at 65ºC. The lower heater thermostat is set at the higher temperature, firstly to obtain the maximum storage, without risking dangerously high temperatures; and secondly, to allow for the very small drop in temperature of the water during the day, due to standing heat loss and the introduction of cold water to replace the hot water that has been used. If hot water is supplied using an off-peak tariff its usual to install a minimum of a 210-litre cylinder, this minimises the amount of on-peak use.

Bits 'n pieces - Heating : Very cold days - on very cold days a higher proportion of direct acting heating will be needed to maintain comfort temperatures / Chimneys - storage heating should not be used in a house with chimneys unless an effective restrictor fitted / Storage Core - Material: High density bonded magnetite bricks / Heating Element - Type: Incoloy sheathed in units of 850W / Thermal Insulation Front and Rear Panels – microporous silica / Top and Ends – resin free mineral wool / Base – calcium silicate slab

Bits 'n pieces - General : Energy cannot be created or destroyed, but can only change from one form to another / On peak rates daytime higher cost - Off peak rates nighttime cheap cost / Boost would be a 13a convector / panel / 2 bar electric fire etc / Base - would be 20a E7 or E10 night price storage / SAP - Government's Standard Assessment Procedure / Cable should be 1.0m, 4 core cable (live, neutral, earth, pilot) supplied fitted to each heater / E10 is used as a generic term to describe Restricted Hour Tariff [RHT] Meters

Bits 'n pieces - Water : Immersion [Boost] Heater - I have never used one in 35 or more years of E7 / Water should never be heated to less than 55°C as this could cause legionnaires disease / A BS Kitemarked insulating jacket, 75mm or 3 inches thick, costing £15 will save you around £40 a year, an E7 cylinder should have 60mm of sprayon insulation / Domestic heating immersion elements are typically rated at 3kW, although lower ratings are available / Scale builds more quickly at temperatures in excess of 60ºC and thermostat settings should not generally exceed 65ºC / The top element is a manual 60 minute boost, that automatically switches off / The bottom element is automatically controlled by your electricity supplier see #32 / Smaller dwellings, eg low occupancy, or sheltered accommodation, often have cylinders smaller than 210 litres / An E7 cylinder will have 60mm of insulation, double the value of a non-E7 cylinder

Bits 'n pieces - Wiring & Circuits

Generally a maximum of 100 amps is supplied to domestic property and comes into your home from the suppliers meter to your fusebox. At this point everything from the suppliers meter [tails] is the householders responsibility. The fuse box is a kind of distribution centre that splits the separate circuits such as cooker / night store / lighting and what we call power points or 13a sockets. Modern dwellings have a fuse box called a consumer unit, with one main isolating switch controlling the whole house supply, older homes have a number of separate fuse boxes controlling the supply to individual circuits, each often has an individual separate isolating switch. Where a circuit supplies a single major appliance such as night store heaters and water heaters [or cooker] the cable runs directly to it from the consumer unit fuse or MCB, via a control unit or a fused spur connection. Here I'm only concerned with night store heating and night store water supply. Your water heater controller looks something like this .. or .. this Both the water heating & night store heaters are switched on by a radio signal out of your control and run on their own exclusive 20a radial or ring circuit. If anything ever goes wrong with these circuits you really need an electrician to help you, its not something the unwary should ever attempt.

NOTE01 : Efficiency a widely misunderstood term in electric heating. Electric energy is converted to heat with 100% efficiency at the point of use, therefore any electric heater is 100% efficient .. .. If you pay for 1kWh of electricity .. .. then 1kW of heat will be transferred into the room .. .. for one hour.

NOTE02 : Heat load calculator here 'R value - walls floors etc calculator here 'U factor - windows calculator here

NOTE03 : People often ask what is the % of use split between night & day, confusing answers are given between between 15 + 50%, here's a page that lists all suppliers recommended split figures. Importantly Focus research shows that 38% of E7 customers don't even have storage heaters and/or don't regularly use appliances at off peak times.

NOTE04 : Lots of people ask what is inside, see here for different types.