One of the main tasks in your hobby greenhouse will be controlling the environment in the greenhouse, keeping the heat and the cold at bay for a great growing condition. I have spent many hours wondering how the ventilation in my greenhouse works, there is such a breeze on some days and others it is just plain hot and humid feeling outside but using my fans and the vents in the greenhouse in combination with a shade cloth I have been able to keep my greenhouse thriving even in the summer months.
You also need to be aware of high temperatures even in the winter months. It is important when you first start using your greenhouse that you watch the sun and the heat in the greenhouse over the first few months until you know how to regulate the temperature best. If you are using a heater with out a thermostat, and the sun has been shining all day, it can easily reach ninety degrees or higher inside the greenhouse when it is only ten degrees outside! When it has been sun shining all day and you are running a heater in the greenhouse, the heat will accumulated inside and your plants could suffer. In the summer, when the heat and the sun is high, you need to keep your vents open for most of the day. In the early spring and in the later summer you will need to close the vents on the greenhouse because the night air might be a little too cold and the plants could get frosted putting you back at square one for the growing season.
During the summer, your vents and doors that are open should be about twenty to twenty five percent of your floor area, which will ensure that breezes will be swept in to the greenhouse area. Roof vents allow for heat to escape from the greenhouse, and sidewall and door vents allow air to flow into the greenhouse to push out the heated air. If you are not able to be in the greenhouse there are many automated and timer controls that will open the vents at certain times or at certain temperatures, which will ease your mind when you know it is going to be a hot day.