Maintaining a constant temperature in your greenhouse/growroom is not as easy as you may think. Even in the British climate you may have to consider a means of cooling as well as heating it.
Active cooling is usually dealt with by drawing cooler air in with a fan, exhausting the hotter air to the outside.
Passive cooling may involve opening the top vents manually or with temperature controlled opening devices.
Here we discuss heating and temperature control - which methods should you choose?
You can heat using electrical devices, paraffin-based heaters or gas-based heaters, the choice depends on two things:
1. do you have or can you provide a local electricity supply?
2. what accuracy of temperature control do you want?
Paraffin heaters generally have no means of maintaining a constant temperature, they are either on or off. Yes you can adjust the heat output but you'd have do this every time the good old British weather affects the temperature in your greenhouse; adjusting for daytime and again for night time. They do smell a bit too.
Gas heaters are often more sophisticated. They come with a built-in thermostat which regulates the flow of gas and thus the heat output, controlling the greenhouse temperature to within 3 degrees of your setting. Often quite bulky due to the gas bottle being stored internally they take up a fair amount of space but if you have no electricity supply available they're a better bet than the paraffin type.
Electric heaters tend to come in three forms: there's the tube type, usually fixed to a wall or the floor near the base of the greenhouse, the fan heater type which can be placed anywhere its trailing cord will allow and finally the heat-mat or heat-tape types which are used for very localised heating under seed trays. All are available with thermostatic temperature control, just like the heating in your house. This method of heating offers the widest choice of products and with the exception of the fan heater is fully waterproof so you don't have to worry about watering near them. Again, if you choose a model with a built-in thermostat it will control the greenhouse temperature to within 3 degrees of your setting.
Accurate temperature control will only be achieved if you install methods for cooling and heating. Even then the thermostats which are integral to the heater, or indeed the independent mechanical ones both measure locally; you can't put the thermostat where your most sensitive planting is. For electric heaters this can be remedied using an separate thermostat with a trailing sensor cable; you can place this anywhere in the greenhouse and the thermostat will switch your heater on and off as necessary.
More choices now, there are two types of trailing sensor thermostat!!
Capillary types rely on the pressure of air contained within a thin tube to vary according to temperature; they control to within 3 degrees of the setting on the dial. This means that if it switches off your heater at 20C the temperature will fall to 17C before the heater switches back on again.
Electronic types use a sensor at the end of a trailing cable which relays the temperature back to the switch box. These vary from make to make but the best ones switch on just 1C below the switch off point. This differential is called 'hysteresis'.
Both types are available with waterproof switch boxes.
So in summary, you should consider methods for heating and cooling. For heating, if you have no power source nearby we'd recommend a gas heater. If you have power then use a waterproof electric heater with a separate thermostat. Finally, if you want minimal temperature fluctuation choose an electronic thermostat.
We make no apologies now for introducing you to our electronic thermostat the PD-012, you'll find details on our Products page. They are available from 1st September every year via eBay.
Active cooling is usually dealt with by drawing cooler air in with a fan, exhausting the hotter air to the outside.
Passive cooling may involve opening the top vents manually or with temperature controlled opening devices.
Here we discuss heating and temperature control - which methods should you choose?
You can heat using electrical devices, paraffin-based heaters or gas-based heaters, the choice depends on two things:
1. do you have or can you provide a local electricity supply?
2. what accuracy of temperature control do you want?
Paraffin heaters generally have no means of maintaining a constant temperature, they are either on or off. Yes you can adjust the heat output but you'd have do this every time the good old British weather affects the temperature in your greenhouse; adjusting for daytime and again for night time. They do smell a bit too.
Gas heaters are often more sophisticated. They come with a built-in thermostat which regulates the flow of gas and thus the heat output, controlling the greenhouse temperature to within 3 degrees of your setting. Often quite bulky due to the gas bottle being stored internally they take up a fair amount of space but if you have no electricity supply available they're a better bet than the paraffin type.
Electric heaters tend to come in three forms: there's the tube type, usually fixed to a wall or the floor near the base of the greenhouse, the fan heater type which can be placed anywhere its trailing cord will allow and finally the heat-mat or heat-tape types which are used for very localised heating under seed trays. All are available with thermostatic temperature control, just like the heating in your house. This method of heating offers the widest choice of products and with the exception of the fan heater is fully waterproof so you don't have to worry about watering near them. Again, if you choose a model with a built-in thermostat it will control the greenhouse temperature to within 3 degrees of your setting.
Accurate temperature control will only be achieved if you install methods for cooling and heating. Even then the thermostats which are integral to the heater, or indeed the independent mechanical ones both measure locally; you can't put the thermostat where your most sensitive planting is. For electric heaters this can be remedied using an separate thermostat with a trailing sensor cable; you can place this anywhere in the greenhouse and the thermostat will switch your heater on and off as necessary.
More choices now, there are two types of trailing sensor thermostat!!
Capillary types rely on the pressure of air contained within a thin tube to vary according to temperature; they control to within 3 degrees of the setting on the dial. This means that if it switches off your heater at 20C the temperature will fall to 17C before the heater switches back on again.
Electronic types use a sensor at the end of a trailing cable which relays the temperature back to the switch box. These vary from make to make but the best ones switch on just 1C below the switch off point. This differential is called 'hysteresis'.
Both types are available with waterproof switch boxes.
So in summary, you should consider methods for heating and cooling. For heating, if you have no power source nearby we'd recommend a gas heater. If you have power then use a waterproof electric heater with a separate thermostat. Finally, if you want minimal temperature fluctuation choose an electronic thermostat.
We make no apologies now for introducing you to our electronic thermostat the PD-012, you'll find details on our Products page. They are available from 1st September every year via eBay.