Electric heating

The Wiki strikes again... another one for review
This article compares the various types of electric space heating.
==All types=A few things apply to all of them.
All electric heaters are 100% efficient, none of the heat goes outdoors.
All are exempt from the annual inspections required of gas appliances in rented properties.
==Plug in heaters==These are all much more expensive to run than all other mainstream heating options, at around 3-4x the energy cost of mains gas.
Thermostatic models prevent room overheating, which wastes money & energy.
Plug-ins are best suited to just occasional use, where their high run cost and zero installation cost makes sense.
==n heater==High energy cost, usually fairly high power, fast heating, small, noisy, fire risk if covered.
===Convector==High energy cost, medium power, medium size, no noise, less fire risk if covered.
===Electric Radiator==High energy cost, lowish power, slow, large. Some only reach a moderate temperature, and are touch safe, no fire risk, and can be used to dry clothes. Some get hot enough to burn things though. Relatively good around kids and the infirm, though they're heavyish and can be knocked over. More tolerant of minor water spills than most other portable heater types. Some have a radiator temperature control, some don't.
==r fire==These radiate heat from a red hot bar. Older models tend to be dangerous, with an exposed red hot live bar, inadequate guarding, and they tend to catch fire if something falls on them. They also seem to attract naughty kids that like to experiment. New models have improved guarding, but no other benefit.
Replacement heating bars are available if one fails, but a better heater is usually preferable.
===Halogen heater==A more modern version of a bar fire, these use a red halogen lamp in place of the bare bar. The lamp is insulated rather than bare & live. The heat density isn't as high (400w per bar is typical), reducing the fire risk.
The halogen lamps last far longer than visible light lamps, but they don't last forever. Replacement infra red lamps are available.
===Tubular heater==Tubular heaters are low power (typically from 60w to 300w) and low power density heaters designed to remain safe if a coat etc falls on them. These are used where items might fall on them, for pipe freeze protection, to keep frost off greenhouses, etc. The safest of all plug- in heater types. More tolerant of minor water spills than most other portable heater types.
==Heat pump=There's only one type of electric heating that can beat 100% efficiency, and that's a heat pump. These can give equivalent to 300% efficiency by using the leccy to pump heat in from outdoors. Since all heat pumps take heat from outdoors, they must be installed one way or another.
===Air source heat pump==Air source heat pumps are the cheapest heat pump. These use a coil and fan to extract heat from the outdoor air.
The downside of air source heat pumps is that efficiency and hence energy delivery falls as outdoor temp falls. When the outdoor coil freezes, which happens somewhere in the region of 5C and below, efficiency drops much further, making them ineffective heaters at such times.
Sometimes the units are reversable, also able to operate as air conditioning in summer.
===Ground source heat pump==The downsides of ground source heat pumps are that a huge and costly layer of ground tubing needs to be laid. This takes a large area of ground.
===Geothermal source heat pump==The downside is installation cost: a bore hole must be drilled, and a long heat source tube lowered into the water in it. These use less than a square foot of land.
==Storage heaters=These heat up a pile of firebricks overnight on cheap rate electricity (using economy 7 & similar schemes). During the day the stored heat is let out by controlled flaps.
The main downside of storage heating is poor controllability, poor weather prediction, and sometimes they run out of heat before recharging time. Some newer models access weather forecasts in a bid to improve performance, how successful this is I don't know.
Storage heaters are bulky compared to radiators.
Storage heating is the second cheapest method of electric heating to run (only heat pumps cost less), and its suitable for all weathers, making it one of the most common choices. The run cost is still significantly higher than mains gas.
Note that daytime rates are often slightly higher on E7 type schemes, so the savings tend not to be quite as good as they appear.
==Under floor heating=UFH is available in piped water and electric forms. The electric version is much more expensive to run.
The main advantages of UFH are that no heating equipment is visible, and it provides a comfortable warm floor. The warmth is especially appreciated with a tiled floor, and in bathrooms.
When installed on a ground floor it requires [[insulation]] underfloor. Usually this means taking up the existing floor, but there are thin insulation boards that allow heating to be laid on top of an existing floor.
UFH can't usefully be powered by cheap rate electricity. UFH has a significant time lag, so must be timed to turn on before the heat is needed. For these reasons, electric ufh is inherently not a cheap option. Heating cable failure can occsaionally happen, and this creates additional expense if the floor is tiled or otherwise permanently finished.
Pipe based ufh driven by the central heating boiler is preferred wherever this is usable, as its much cheaper to run, and more reliable long term.
==Halogen radiant=Wall mounted halogen radiant heaters produce radiant heat plus red light. The principle is exactly the same as halogen plug-in heaters, and their shortcomings the same. They bneed to be mounted high up to reach all areas of the room, and the amount of red light given out at near eye level can cause some visual discomfort. For this reason they tend to see more use in commercial spaces.
==Obsolete=Obsolete types of electric heating are still occasionally encountered.
==iling radiant heat==Ceiling mounted radiant heaters are occasionally seen in 1960s properties. Since heat rises, these give poor performance, with rooms cold at the floor and hot near the ceiling. This increases energy use and losses.
===Bowl heater==These were popular from the 1920s to 50s, but are rarely seen today. These are economical radiant heaters for use in cold houses, as more of the radiant heat is directed to the person sitting nearby, compared to a bar fire. Usually rated at a few hundred watts, these are intended to take the chill off an otherwise unheated space.
They have all the defects of bar fires, plus instability, which increases the fire risk further. Also their age makes them generally fail to meet even basic electrical safety standards. They have little chance of passing a PAT test and should not be used.
==See Also=* [[Insulation]] * [[Heating]] * [[Special:Allpages|Wiki Contents]] * [[Special:Categories|Wiki Subject Categories]]
[[Category:Heating]] [[Category:Electrical]]
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snipped-for-privacy@care2.com wrote:

At point of use...

Other advantages include: the don't generally introduce extra moisture into the room.

A comparison to oil and LPG might be useful.

That does not quite read right - how about "Thermostatic models prevent room overheating, which saves energy and money"

Many fan heaters have a lower power setting - typically 800 - 1000W. This is small enough to run from a standard mechanical thermostat. This makes them (especially when wall mounted) ideal for frost protection in things like tool stores or workshops.

Do we need the "high energy cost" prefix to every paragraph? - The point has been made in the introduction.

Might be worth pointing out that these are effective at heating people rather than rooms - hence less power can be used to keep you feeling warm when in a cold environment. Handy for workshops, sheds etc.
Can also be used as patio heaters - since they will radiate heat at people and are not affected by draughts etc.

Typical application includes use in airing cupboards, and for reducing condensation and mould in problem areas.

Not sure that reads well as a section intro...
Something like:
Heat pumps transfer heat from one place to another. Typically from outside of a building to the inside. The energy they consume is also output as heat. Hence they are the most efficient electrical heaters available, since thy will actually contribute more energy to a room than they consume.
There are several types including:

"Air source heat pumps are the most common form of heat pump. They are often built into air conditioning units. By changing the direction in which they are pumping they can be used to heat in the winter and cool in the summer. "

a limitation of ->

don't really need that last bit

What about the upsides? Better ratios, can be used for cooling as well, can be used for heating thermal stores and not just air etc.

Many of the advantages of ground source, but without the need for significant areas of land to be used for piping. These use a borehole drilled into the ground - preferably into the water table.

don't need the rest

I would put these after plug ins and before heat pumps since they sit between them in running costs.

Could we reword "controlled flaps" somehow?

they also frequently don't fit typical patterns of usage - giving out lots of heat when no one is home and starting to cool just when you need them most.

One aught to include a heat bank here. This avoids the controllability and delivery time limitations of the conventional storage heater since it behaves as a wet central heating system but with the heat being stored it the store water until it is required. Also makes it easier to augment the electrical heating with other sources like solar, solid, fuel etc.

see heat bank above...

already done this one toward the top of the article...

If they are predominantly radiant, then the heat will not be rising necessarily ;-)

Not bad. The tone could do wit a little lightening in places - it tends to dwell on costs and downsides. It would be handy if it gave hard information on getting the best from electric heating (i.e. some of the less common stuff like supplementary thermostats, heat pumps, thermal stores etc) - especially when in some cases that is what a user will be stuck with.
--
Cheers,

John.

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We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember John Rumm

Ditto all that for IR lamps, missed out entirely.
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Thanks for the effort you (and others) put in to getting these articles together.
I feel there is some confusion in the term plug-in. I have seen quite a few built-in electric fires (fan and bar) which in every other way are equivalent to the plug-in models.
Back in the 60s we had a bar fire which had its heating wires within quartz tubes. Not, I think, covered. (Are they still available? Or is this just an historic footnote.)
--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
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I've seen what was then a quite common ceiling heat/light combo advertised quite recently, and mentioned here. Dimplex did a very common 750W wall mounted version too, which I haven't noticed recently.
They are silica glass tubes, and for the purposes of PAT testing, the silica glass is considered to be a live part (which means most of the 60's ones won't have good enough finger guards nowadays to stop you touching the tube).
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
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Andrew Gabriel wrote:

A very good idea simply because they get so hot!
Which made me think, I'd quite like electric fires to switch off entirely of the power fails. I can imagine a situation in which a fire is just left but something is put on/near/dropped onto such a fire during a failure - and forgotten/missed in the dark that often accompanies power cuts. Even just the waste of power that could occur might be a reason!
--
Rod

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You want one of these: http://www.poolewood.co.uk/acatalog/No_Volt_Release_Switches.html
And the styling is so in tune with the domestic setting!
--
Jón Fairbairn snipped-for-privacy@cl.cam.ac.uk
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2009-01-31)
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Jon Fairbairn wrote:

Would be fine in the nursery with the Duplo... :-)
(Yes - in principle, exactly right. Should be built-in. Surely it wouldn't cost 21.70 *extra* to do so?)
--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
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Yes!
I'm not sure, now I think about it. If there's a thermostat in there that simply interrupts all the current, it'll run till the room's up to temperature and then switch off permanently...

Not a bad idea. It could then be done with a work-round for the above problem.

No, but they might charge that much extra.
My pet peeve in this line is the valves in gas cookers that shut the gas off when the lid is closed -- but turn it back on without igniting it when it's opened again.
--
Jón Fairbairn snipped-for-privacy@cl.cam.ac.uk
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2009-01-31)
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Jon Fairbairn wrote:

But even if a thermostat cuts out current, it won't remove volts from the supply, will it?
--
Rod

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True. It depends precisely how those switches work; if they live up to their name, they're exactly right. I'd assumed a certain design, which is probably wrong!
Incidentally, the cheapest on that page is under £15.
I suspect the reason I got the wrong idea is that what I'm looking for myself is a slave socket arrangement like the ones on dust extractors, so that I can DIY a dust cyclone and have it turn on with the tool. I can find ones intended for PCs (daft: just get a distribution board with one big switch), but haven't found the info to show whether they're rated for the amount of current a power tool + vacuum take.
--
Jón Fairbairn snipped-for-privacy@cl.cam.ac.uk
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2009-01-31)
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HI
snipped-for-privacy@care2.com wrote:

<<big snip>>

IT's not so much the tube that's costly - but burying it in the ground... - especially if you already have a nicely-landscaped garden!
Over here (South-West Ireland), lots of new-build houses require significant amounts of earth to be moved around at the initial stages to create a level plot - and if the collector tubes can be installed while the other ground works are being carried out then it's only an extra day's 'digger time'.
You can also collect heat from a decent-sized pool or river - in which case the installation costs are minimal...
Adrian
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Ok, version 2 for your perusal...
This article compares the various types of electric space heating.
==Radiation vs convection=First its helpful to explain something. Heat is given off in 2 possible ways, radiation and convection. * Radiation in this context has nothing to do with nuclear radiation, it simply means that the heat travels in a straight line through air, just like light. * Convection is the upward movement of heated air. Hence its not unusual to see convection heaters having a chimney shape to maximise air movement. * Heat is also conducted, but this is a minor effect with space heating.
Red hot heating elements primarily radiate heat, dark less hot elements primarily convect. all radiant heaters produce a substantial amount of convected heat as well. Halogen heaters produce the highest percentage of radiated heat.
Radiated (or radiant) heat turns to heat when it hits a solid object. This effect can warm humans in a cold environment with less heating of the space, and this effect is used to advantage in industrial situations to save heating power. However working in a cold room near a red hot element gives uneven & inconsistent heating, and the result is far from as comfortable as proper space heating.
=All typesA few things apply to all of them. * All electric heaters are 100% efficient, none of the heat goes outdoors. ** although electricity generation at the power plant is inefficient * All are exempt from the annual inspections required of gas appliances in rented properties. * Electric heating doesn't introduce any moisture into the house, as some types of fuel heating do.
==Plug in heaters==These are all much more expensive to run than all other mainstream heating options, at around 3-4x the energy cost of mains gas.
Thermostatic models prevent room overheating, which often happens with non-thermostatic models. Thus they cost less to run.
Plug-ins are best suited to just occasional use, where their high run cost and zero installation cost makes sense.
==n heater==Usually fairly high power, fast heating, small, noisy, fire risk if covered.
===Convector==Medium power, medium size, no noise, less fire risk if covered.
===Electric Radiator==Lowish power, slow, large. Some only reach a moderate temperature, and are touch safe, no fire risk, and can be used to dry clothes. Some get hot enough to burn things though. Relatively good around kids and the infirm, though they're heavyish and can be knocked over. More tolerant of minor water spills than most other portable heater types. Some have a radiator temperature control, some don't.
==r fire==These radiate heat from a red hot bar. Older models tend to be dangerous, with an exposed red hot live bar, inadequate guarding, and they tend to catch fire if something falls on them. They also seem to attract naughty kids that like to experiment. New models have improved guarding, but no other benefit.
Replacement heating bars are available if one fails, but a better heater is usually preferable.
===Halogen heater==A more modern version of a bar fire, these use a red halogen lamp in place of the bare bar. The lamp is insulated rather than bare & live. The heat density isn't as high (400w per bar is typical), reducing the fire risk.
The halogen lamps last far longer than visible light lamps, but they don't last forever. Replacement infra red lamps are available.
===Tubular heater==Tubular heaters are low power (typically 60w to 300w) and low power density heaters designed to remain safe if a coat etc falls on them. The safest of all plug-in heater types. More tolerant of minor water spills than most other portable heater types.
These are used * where items might fall on them, eg coats * for pipe freeze protection, * to keep frost off greenhouses * in airing cupboards * to dry a small area with a damp or mould problem * etc
===Fire==Plug-in or fitted fires with wooden surrounds usually use bar elements to provide heat, and thus behave like bar fires.
These often use a red lightbulb to light fake coals. The heat from the bulb causes a slight convection current, which turns a lightweight slotwheel above the bulb. Fitting a lower power lamp often stops the slotwheel rotation.
==Heat pump=There's only one type of electric heating that can improve on 100% efficiency, and that's a heat pump. These use the pwoer to pump heat from one place to another, and the power they use turns to heat too. When set up to pump heat from outdoors to inside, they can pump 3x as much heat into a room as the power they use.
Since these take heat from outdoors, they must be installed.
===Air source heat pump==Air source heat pumps are the cheapest and most common type of heat pump. These use a coil and fan to extract heat from the outdoor air.
A significant limitation of air source heat pumps is that efficiency and hence energy delivery falls as outdoor temperature falls. When the outdoor coil ices up, which happens somewhere in the region of 5C and below, efficiency drops much further, making them ineffective heaters at such times.
Sometimes the units are reversable, able to operate as air conditioning in summer or as heaters in winter.
===Ground source heat pump==The downsides of ground source heat pumps are that a huge and costly layer of ground tubing needs to be laid. This takes a large area of ground.
These don't ice up like air source pumps, so continue to work all through winter. Since underground temp is higher than outdoor air temp at these times, they also work more efficiently.
These have also been used to heat thermal stores, though their efficiency in this mode is less.
===Geothermal source heat pump==These have the same advantages as ground source heat pumps, but don't need the land. A bore hole is drilled to below the water table, and a long heat source tube lowered into the water in it. These use less than a square foot of land.
==Storage heaters=These heat up a pile of firebricks overnight on cheap rate electricity (using economy 7 & similar schemes). During the day the stored heat is let out by movable flaps.
The main downside of storage heating is poor controllability, poor weather prediction, and sometimes they run out of heat before recharging time. Some newer models access weather forecasts in a bid to improve performance, how successful this is I don't know.
Storage heaters are bulky compared to radiators.
Storage heating is the second cheapest method of electric heating to run (only heat pumps cost less), and its suitable for all weathers, making it one of the most common choices. The run cost is still significantly higher than mains gas.
Note that daytime rates are often slightly higher on E7 type schemes, so the savings tend not to be quite as good as they appear.
Some of the oldest storage heaters had inadequate controls. if you have these in your house, you may find they warm the house during the day when you're at work, and the heat runs out in the evening when its wanted.
==Heat bank=An electrically powered heat bank can be used to run wall mounted radiators. Installation cost is higher than wall mounted heaters, but other heat sources such as solar or solid fuel can be added to the heatbank.
The heatbank stores heat, though the heat capacity is limited. This method is suitable for insulated flats with low heating needs. The ability to run on economy7 dramatically reduces bills compared to non- storage types. The storage effect also enables the peak heat output of the radiators to be much higher than wall mounted electric heaters of the same power as the tank heating element, thus these systems give faster house warm up. The central heating radiators are much less intrusive than electric storage heaters.
==Under floor heating=UFH is available in piped water and electric forms. The electric version is much more expensive to run.
The main advantages of UFH are that no heating equipment is visible, and it provides a comfortable warm floor. The warmth is especially appreciated with a tiled floor, and in bathrooms.
When installed on a ground floor it requires [[insulation]] underfloor. Usually this means taking up the existing floor, but there are thin insulation boards that allow heating to be laid on top of an existing floor.
UFH can't usefully be powered by cheap rate electricity. UFH has a significant time lag, so must be timed to turn on before the heat is needed. For these reasons, electric ufh is inherently not a cheap option. Heating cable failure can occsaionally happen, and this creates additional expense if the floor is tiled or otherwise permanently finished.
Pipe based ufh driven by the central heating boiler is preferred wherever this is usable, as its much cheaper to run, and more reliable long term.
==Halogen radiant=Wall mounted halogen radiant heaters produce radiant heat plus red light. The principle is exactly the same as halogen plug-in heaters, and their shortcomings the same. They bneed to be mounted high up to reach all areas of the room, and the amount of red light given out at near eye level can cause some visual discomfort. For this reason they tend to see more use in commercial spaces.
==Glass element=These are the predecessor of halogen heaters, and they operate very similarly. They use a glass-like quartz tube a few feet long with a heating wire spiral inside it. These are sometimes seen in bathrooms installed in the 60s or 70s.
Compared to halogen heaters they're longer, produce a little lower percentage of radiant heat, and take 10-20 seconds to warm up. They're typically 250w - 1kW.
==Obsolete types=Obsolete types of electric heating are still occasionally encountered.
==iling radiant heat==Ceiling mounted radiant heaters are occasionally seen in 1960s properties. Since heat rises, these give poor performance, with rooms cold at the floor and hot near the ceiling. This increases energy use and losses.
===Bowl heater==These were popular from the 1920s to 50s, but are rarely seen today. These are economical radiant heaters for use in cold houses, as more of the radiant heat is directed to the person sitting nearby, compared to a bar fire. Usually rated at a few hundred watts, these are intended to take the chill off an otherwise unheated space.
They have all the defects of bar fires, plus instability, which increases the fire risk further. Also their age makes them generally fail to meet even basic electrical safety standards. They have little chance of passing a PAT test and should not be used.
==rbon lightbulb==Carbon filament lamps were once used as frost protection heaters in unheated bathrooms & toilets. A 200w carbon filament lamp provides about as much light as a 40w bulb, though with an orangey colour. The advantage is that no electrical wiring or socket is needed, the bulb is simply put in the bulbholoder and left switched on.
=Other Applications==Frost protection=It requires much less energy to use a heating tape applied to frost- vulerable pipes rather than heat the whole room. Nevertheless space heating is sometimes used for frost protection.
Some heaters have thermostats that go low enough to provide freeze protection. 5C is the usual setting, and allows a margin for temperature variation through the room.
Many heaters are under 1kW, or can be switched to this low a power setting. These can be run directly from a bimetal thermostat. Fan heaters have the advantage that they can be mounted above head height, blowing downwards.
==Patio heating=Patio heaters can extend the outdoor season to some extent. However they're power hungry and much of the heat simply blows away. Opinions on the wisdom of patio heating remain mixed.
Heating people outdoors requires radiant heat. Convected heat simply blows away. Most of the radiant heat misses its target. To maximise efficiency the heater should be as close to the people being heated as is safe.
The most efficient radiators are halogen heaters. Bar fires also radiate, but the percentage of heat radiated is less, and the percentage drops significantly in wind.
=See Also* [[Insulation]] * [[Heating]] * [[Special:Allpages|Wiki Contents]] * [[Special:Categories|Wiki Subject Categories]]
[[Category:Heating]] [[Category:Electrical]]
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We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember snipped-for-privacy@care2.com saying something like:

I recall them, yes. Fitted in many bathrooms years ago.
The IR lamp I referred to was this type... http://www.uklightbulbs.co.uk/cgi-bin/site-editor.pl/8/-ecommerce?action=item ;item=INF3;eid09856 Often used by livestock breeders to warm puppies, etc, but is really very useful for spot heating of pensioners at very little cost.
A handy heatproof holder can be found here... http://www.ukdogruns.co.uk/infra-red-heat-lamps.php
The IR lamps can be found much cheaper from farmers' supply stores and electrical wholesalers.
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Bar fires with wooden surrounds provide a comfortable but expensive form of heating for a lounge. In traditional older style homes this type of appliance was often situated in the fireplace replacing a coal fire. It continued to provide both the focal point of the room and a source of radiant heating somewhat similar to the coal fire, warming the legs and feet of those sitting around it, but without the work and smoke.
The fires were fitted with two independant bars. In normal moderate conditions one bar (1.5 Kw) was usually adequate, but in cold conditions it was better to use a separate additional convector heater than put on both bars as 3 Kw would be too fierce to sit near. The bar fires might have been better fitted with one 1.5 Kw and one 750 W element rather than two elements of the same rating.
Bar fires with wooden surrounds have live bars and exposed live bar supporting bracketry.

The red light adds a warm ambience to the room and would normally be put on even if the heating elements were not required. Reducing the number of bulbs to one (colourless) of lower rating was generally more agreeable and economical.

UFH seems to encourage the appearance of significant quantities of fluff and dust on the floor.
Roger R
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On Wed, 04 Feb 2009 19:56:44 -0800, meow2222 wrote:

Do you get baseboard heaters in the UK? I don't remember ever seeing them, but I'd be surpised if they're not available. As implied, they're only about 6" tall and placed around the perimeter of the room at floor level, and use a heating element covered in lots of aluminium fins (covered in a metal casing with vents at the top).
We've got quite a lot at our place here, running from cheap-rate electric (which works out at about 3p/KWh - propane in comparison is about double that for the same heat output)
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Some points to add...
E7 storage heaters. E7 storage heater generally suffer low retention, that is up to 60% of heat is convected out overnight with a mere 40% of heat retained to maintain temperature through the subsequent evening before the next charge period. The wrong solution is to oversize the heater in order to retain sufficient heat by evening - it will, but you will barbecue from about 4am onwards as the heater top damper opens full bore. Equally wrong is undersizing - they will be cold & useless, relying excessively on peak-rate electricity to compensate.
Conventional E7 storage heaters are of little use a) if you are out working during the day (ie, not a pensioner) as their heat diminishes by the time you return or b) poorly insulated.
E7 storage heating is about getting as much insulation as possible before hand: 200mm+ of loft insulation, cavity wall insulation (CWI) and all glazing/door sales in good working order. Check even if you have CWI whether any walls are solid, often bathroom or corner room walls are, anything over a porch or entry, or even all the upstairs in older houses. Double glazing is obviously good, but the payback period is so long (up to 164 years) it can be better to tackle other alternatives first. Double glazing saves 50% of the heatloss through your windows, not 50% of your overall heatloss if you do not already have loft & CWI insulation.
An improvement to conventional E7 storage heater is to use E10, an afternoon-boost tariff. This typically gives 3 charge periods bringing the heater & house back up to temperature. Unfortunately a special tariff can hold you hostage to an insufficient number of suppliers to achieve price competition - either now or in the future. This is particularly the case with non-storage electric heating where claims are often entirely dependent on such tariffs.
Improved E7 storage heaters, such as Dimplex Duoheat & Creda Eco, use a peak-rate boost element. These work on the basis that the heater core even when appearing cool still has the ability to heat air some way above ambient, so requires only a small supplemental element (eg, 0.29-0.39kW) to boost the heater casing temperature to a meaningful delta above ambient. Whilst they work if 1) insulation is satisfactory 2) they are sized adequately. Undersizing in output or number will result in excessive use of peak rate electricity, their maximum output is 2.55kW rather than 3.3kW of conventional units often necessitating 2 units which greatly increases cost (2x 380 vs 1x 420). Additionally they add complexity which could impact on reliability - unknown 10yr+ availability of PCB electronics & thin-film elements compared to conventional storage heater which is simply a box of "resistor elements + bricks + capillary electromechanical thermostat" for 25yr+ life. It is said that conventional storage heaters do not fail, they are buried with the previous occupiers.
E7 storage heaters of the slimline variety can also be had with a fan, which seems of dubious use since the design is a high convective type so the fan will merely extract more heat from the core faster. The fan is best used with peak-rate element to avoid heat stratification that otherwise can occur.
A significant improvement to conventional E7 storage heaters is to use commercial units. Commercial E7 storage heaters have vastly higher retention rates, 40% of heat some 17hrs after E7 has finished, which allows them to be sized to avoid the overnight roasting & cold subsequent evening. This is achieved by increased use of silica block & no top venting core damper opening part way through the charge period. Instead a fan extracts heat as required on-demand via a case mounted or wall mounted thermostat dial. Whilst this partly solves the problem of "house roasted by convection oven" it comes at a stiff penalty in terms of size (typically 285mm deep) and price (typically 800-1400 a unit). So just 2 heaters cost the same as a high-end combi installed.
In summary E7 storage heating can work, but it relies on careful sizing & substantial levels of insulation. Even then the commercial solutions are not particularly good, just better than bad. The fan is a failure point,
Electric wet / hydrionic heating. This may be the migration step someday if UK gets sufficient nukes, but probably not as currently envisaged. Any electric wet heating must 1) use an afternoon-boost tariff like E10 or b) very large thermal store heated up on E7. Unfortunately many systems (particularly in flats) are not on the right tariff (or not programmed to match the tariff) and do not have an adequately sized thermal store which is "charged" during off-peak pricing. The effect is massive bills and they can even be unresponsive if wet radiators are high water content (fast warmup). To heat a typical semi on an E7 thermal store would be quite a challenge, I suspect 3-4x 250L tanks with 4" of rockwool insulation. E7 is about 5p/unit & peakrate 12p/unit as of 2008, with gas around 3.85p/unit plus adjustment for efficiency ((65)-82-91%) plus adjustment for annual servicing plus adjustment for depreciation (ie, a new boiler fitted is 3500 every 10yrs, more often if a bargain basement combi is used in the south with basic aluminium heat exchanger rather than stainless steel).
A more likely migration step is a heating system utilising heat pump technology - air/ground to water.
Air to air heat pumps. Units from Fujitsu in particular can achieve >2.5 CoP down to -10oC, a temperature that is rarely seen in the UK and very unlikely during the day. Typically a bad January period is -1oC during the day, -5oC overnight. That 2.5 CoP translates into 2.5kW out for 1.0kW in - that 1kW even at peak rate is thus reduced below even gas prices. The counter is a heatpump may have a life of 3yrs (DIY install, poor seals) to 10yrs so either factor in an annual maintenance or depreciation for capital replacement. Lifetime cost directly drives up the real kW cost.
The key barrier to air sourced heat pumps is often noise - whether planning permission is required is unclear in many situations, boundaries can be very close and noise pollution is severely frowned upon. Outdoor units can range from 46-58dB(A) which is quite a substantial figure - not on a par with a Dyson, but not silent either.
Supplementary heating is therefore potentially required at periods below -10oC. However Canada to Sweden routinely adopts heatpump technology in temperatures below that of the UK successfully, the problem is not the real-world CoP with modern invertor units but the noise w.r.t. neighbours who may complain.
Ground to air heat pumps. Ground to air heat pumps have two benefits over those sourcing from the air a) the ground at <1.5m is around 9oC all year round b) there is no noisy fan stuck on your outside wall. CoP can be somewhat better, >2.8-3.2 however the problem is the nature of the ground - extracting "heat" from the ground requires its replacement. Ideally the ground should be a wet clay rather than a dry chalky area to ensure CoP remains high rather than deteriorates. Unsurprisingly the best CoP comes from clay hillside locations or those with access to a nearby spring.
Air/Ground to Water heat pumps. These seem attractive by virtue of their ability to replace existing gas boilers. Unfortunately the water output temperature is restricted - a very high temperature results in very low CoP, a very low temperature results in a very high CoP. Radiators require oversizing (doubling ideally) and DHW requires a boost element (E7 would be ideal). In essence they are best served feeding a wet thermal store, permitting a smaller thermal store to be adopting than would ever be possible with a purely E7 resistance heating solution. A heat store does also permit the winter day/night variations in CoP to be evened out - when CoP is worst overnight it is offset by E7 electricity being considerably cheaper.
Key to Air/Ground to Water heat pumps is to really use underfloor heating (UFH), which can directly use very low water temperatures (35-40oC) so permitting the heat pump to operate with extremely high CoP (5 or greater).
Long term heat pump adoption is likely to increase, but if CO2 systems become available (CoP 5 at <0oC) then the adoption rate globally would increase significantly. Issues then become generation capacity and distribution, areas where the UK electrical system may reflect the planning of its transport system.
With most heating systems it is NOT the cost per unit, it is the lifetime cost in terms of maintenance & eventual capital replacement through depreciation. The latter can add 35-50% of the effective price per unit for gas (although realise not all heating systems are equal in terms of achieved comfort, GCH sets the bar very high to beat).
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Jules wrote:

Yup, two types crop up from time to time. Skirting radiators, which are long pipes with fins like you describe - normally encased in a cover with vents that looks similar to a skirting board but a bit thicker. They often run from the centrl heating though rather than electric.
Also plinth heaters - often used in kitchens under the kitchen units. These are also heated via the wet central heating system, but usually have a fan assistance to speed convection.

What times of the day can you get cheap rate?
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Cheers,

John.

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On Thu, 05 Feb 2009 16:31:33 +0000, John Rumm wrote:

It's rather random - we're running on a load-control program here, so the heaters shut down at peak times (with the propane furnace then taking over) and in return get the cheaper rate. I think they reckon on about 2/3 of the time on, 1/3 off. Looking at the logs, the heaters ran yesterday from 1am to 6am, then again from 8am right through to 7am this morning - it's now 11am and they're still off.
Talking to an engineer the other day, the off-peak meter just slaves off the main one, and they send a 220Hz signal down the line to tickle the load control system into doing its stuff (small controller and a big box 'o relays in the basement - we've got the water heater and clothes dryer on a separate circuit to the heaters)
I'm not sure if such a setup exists in the UK - I've only ever known Economy 7 systems there, which seem to have more predictable cheap-rate periods and don't outright switch stuff off at peak times! (but I'm not sure their rate was quite as good - been a while, though)
It all works reasonably well, except that our propane furnace (and associated forced-air ductwork) isn't the best, so it doesn't heat the house nearly as well as the electric heaters can. I think we'll throw a wood-burning furnace in this year too though, and that'll really sort things out.
(plenty of space for a GSHP here too, but that doesn't seem to have quite entered the DIY arena yet, and I have issues with paying someone else a fortune to come and dig up my back garden when I could do that bit myself :-)
cheers
Jules
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Jules wrote:

Ah, yup that makes cheap rate heating far more useful.

I think most are still the same - cheap rate at fixed times overnight. There may be some tariffs that also give an hour or so of "boost" time during the day - but not enough to make non storage cheap rate heating worthwhile (unless you like it hot at night!)
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