Electric heaters can heat space in two main ways: by convection and radiation.

• Convection heaters use the principle that hot air rises. It expands and becomes less dense and so is pushed upwards by the colder, heavier air, which flows in to take its place. The source of heat must then be at the bottom. Electric heaters often use a combination of convection and radiation to provide efficient, economical heating.

• Radiation duplicates the way in which the earth is warmed by the sun. The radiant heat given off by the appliance travels straight ahead, without heating the air through which it passes. Radiators can be of two types:

  o The fire bar type - has a coil of 4 or 5mm diameter, which is wound in grooves in a slab of fire clay. The wire becomes hot, heating the clay so the whole front of the fire radiates heat.

  o The reflector type - has a rod-shaped element fixed in front of a polished reflector. The stream of radiant heat is directed according to the shape of the reflector, usually bowl or trough shaped.

If a radiator incorporates a fan, this speeds up the warming effect. Such heaters should not be operated without the fan going as the fan also helps dissipate heat from the unit as well as around the room. Without the fan, the unit may overheat unless it incorporates a safety cut-out to prevent this happening.

A radiant heater is only as effective as its reflector. A dull reflector tends to absorb the heat rather than reflect it. Make a habit of cleaning the reflector, at least seasonally. Generally, a good metal polish will do the job but avoid using abrasive products, which may damage the surface. Since there are dozens of different elements for different heaters, if you need to replace an element, make sure the new one is the identical length and rating to the old element. New wire spirals can be fitted to a fire bar element as long as the fire clay is intact, but rod elements usually have to be replaced as a whole.

When replacing the element, make sure the unit is completely unplugged. When fitting a new rod element to the fixed contacts, ensure the screw or the element do not touch the end of the reflector or the guard. Regularly check that the nuts on the screwed contacts are tight as they can cause sparking or a blown fuse if they are allowed to work loose.

Permanent heaters these are designed to be built-in and direct wired. They are usually fan driven and are particularly useful where there are children or elderly people as they are generally safe to touch. Other optional features include thermo­stats, which cut the heater's output back to a pre-set minimum level and turn it up again automatically when the temperature fails.

Solar Heating.
Solar air conditioning systems use solar radiation as the primary energy source to heat or cool buildings. Usually solar collectors and ancillary equipment are used, but some heating and cooling needs can be met using suitable building designs. There are two approaches to solar heating and cooling.

Passive system uses careful building design to control indoor temperatures but no special collecting equipment to capture solar energy. Features of such a low energy building design are concrete slab construction, brick walls, double-glazing, east-west long axis and windows on the north face designed with sunlight control by eaves and windows. The building also has water sprays to evaporatively cool the air and a rock pile to store energy for heating and cooling.

Active system.
Conventional solar collectors supply heated water or air to a building for space heating; to operate a cooling system; or to heat an energy store when surplus energy is available.