The Orte Power Pellets Air Heater is a very good heating device to greenhouses. It can be put in special metal boxes outside greenhouses (so one heater can heat even 4 greenhouses through air pipes). Heating is very ecological and cheap ( up to 70% less costs comparing to oil and gas prophane).

You can steer the heater through GSM, so there’s no need to walk to the greenhouse also sensor can inform You eg: through sms or email  about changes in temperature in the greenhouse.