Greenhouse
basics
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'Natural heating'
Rays from the sun
penetrate glazing and are trapped, as heat, within the building. This is the
'greenhouse effect' working for you, and since the warmth comes free of charge,
it makes sense to catch and hold as much as possible.
A well placed greenhouse, in an
open, sunny spot will attract more solar heat than a building in semi
shade.
Remove summer shading and ensure
that all glass is spotlessly clean. This will maximise solar
radiation.
Permanent or temporary
double-glazing can save up to 50% on winter fuel bills, but remember to arrange
it so that vents can be opened when necessary. Movable thermal blanket
materials are also available and are very efficient - used at night in winter
they will hugely reduce the rate at which heat is lost.
Additional heat
If you
plan to raise plants during winter, you will need additional heat. For the
lowest cost, all that is necessary is to keep the greenhouse frost free - a
safe minimum of, say 2 degrees C - but if you raise minimum temperatures to
between 7 and 9 degrees C, you will be able to grow a much wider range of
plants. This increases heating costs, so you will have to weigh fuel economy
against plant choice.
A maximum - minimum thermometer is essential for setting up your
heating for optimum energy use. Each morning, check the night time minimum in
the greenhouse, and adjust the heating until the desired level is
reached.
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• The simplest and
cheapest heaters burn paraffin. Those with a blue flame and circular wick are
the most efficient, emitting more heat and fewer unpleasant odours than those
with a luminous flame, but their fuel consumption is
higher.
• Bottled gas heaters, which come with a built-in
thermostat and pilot light, are more efficient, since they light up only when
needed. Gas and paraffin heaters produce carbon dioxide when they burn, which
is excellent for plants. However, they also produce water vapour, which
increases the need for ventilation.
• Electricity is the most
convenient form of heating, provided you have a power supply. Heating pipes,
with a separate thermostat, is one option, or you can use a fan heater, either
with a built in or a separate thermostat.
• A low cost alternative
is to use electric soil warming cables. These are laid beneath the greenhouse
soil, preferably in a bed of coarse grit, and act on the same principle as an
electric blanket, keeping roots warm but using minimal energy.
A low cost alternative is to
use electric soil warming cables. These are laid beneath the greenhouse soil,
preferably in a bed of coarse grit, and act on the same principle as an
electric blanket, keeping roots warm but using minimal energy.
Thermostats need careful placing out of direct sunlight but as
close to the plants as possible. Fan heaters, too, should be positioned where
their warm air currents achieve maximum distribution around the greenhouse
without blowing directly onto the plants.
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