When it comes to heating a greenhouse, the planning must be done with care, but also in relation to its future use. We show how the required heat requirement can be determined as precisely as possible and which special features also play a role when heating in winter.
If you want to heat a greenhouse properly, you need to know the outside temperature
If homegrown vegetables are to be harvested all year round, warm and bright places are required for the plants, so that heating the greenhouse becomes an issue by winter at the latest. While there shouldn't be any major problems when setting up a heatable prefabricated greenhouse, the self-builders have to delve a little deeper into the matter, because the first thing to ask is which Determination of the actual heat requirement puts.
The crux of the heat requirement
In order to heat (properly) in winter, we first have to do a little digression into the math. After all, a greenhouse heater is not a bargain and therefore superficial or even incorrect planning would have fatal consequences, not only for the plants in frost. The heat requirement (in W or kW) for heating the greenhouse is calculated from the factors:
Outer surface x U-value x temperature difference
The temperature difference (in °K) is the amount resulting from the difference between the target temperature inside the greenhouse and the local minimum temperature. The latter value is specified by the German Institute for Standardization in DIN EN 12831, which includes a table with the appendix Temperature values of all German cities from 20,000 inhabitants. Here are some examples:
| location | Postcode | Climate zone according to DIN 4710 | Standard outside temperature (°C) | Annual mean outdoor temperature (°C) |
|---|---|---|---|---|
| Berlin | 10117 | 4 | - 14 | 9,5 |
| Hanover | 30159 | 3 | - 14 | 8,5 |
| Hamburg | 20144 | 3 | - 12 | 8,5 |
| Leer (East Friesland) | 26789 | 3 | - 10 | 8,5 |
| Dresden | 01067 | 4 | - 14 | 9,5 |
| Wendelstein | 06642 | 4 | - 20 | 9,5 |
| Brunswick | 38100 | 3 | - 14 | 8,5 |
| Goslar | 38640 | 3 | - 14 | 8,5 |
The outside area can be calculated using the well-known formulas if you want to heat your greenhouse in winter. You can read everything you need to know about the U-values for a wide variety of insulating materials in another article in our garden journal. If you would like to delve a little deeper into the calculation of the heat requirements of greenhouses, you will find the online portal of the Kuratorium für Technik und Bauwesen in der Landwirtschaft e. V. further information and calculation examples.
Heat greenhouse in winter, which is still important
However, the mathematically determined heat requirement can only ever be one of several facts to be taken into account and should therefore only represent a starting point. If heating the greenhouse is an issue for you, it is best to do the math the following considerations into the construction planning one:
- wind situation at the installation site;
- Construction of your greenhouse (height of the base foundation or walls in relation to the window area);
- on-site leaks, thermal bridges, etc.;
- type and location of heating in the greenhouse (in the middle or distributed along the walls; number of radiators; surface heating under the floor);
- Can the heat requirement be reduced by installing insulation (bubble wrap, energy screens, etc.)?;
tips
The use of energy-saving roof coverings can significantly reduce the amount of heat required for heating in winter. For example, covering with 3mm thick glass requires almost twice the amount of energy as building the same house with 6mm thick multiwall polycarbonate.