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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 types=
A 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.


===Fan 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.

===Bar 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.

===Ceiling 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.

===Carbon 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]]