When you start to grow your own weed, one of the first things you learn is the importance of the environment inside your greenhouse.
In order to grow a quality crop, you should have control over temperature and humidity levels that your plant is exposed throughout its life cycle. There are websites such as http://www.climatecontrol.com/blog/automation-indoor-grow-cannabis-facilities/ that provide all the necessary information about the temperature control system.
Temperature is very important to plant marijuana because it sets the stage for rapid growth when you need it, and proper development of buds. Marijuana plants take the same temperature as individuals, so if you feel comfortable in your grow room, they might too.
If your grow room is too cold, your plants naturally will not grow to their full potential. If frozen, they can be damaged or even die. If your grow room is too hot, your plants may be very dense, or they can grow long and thin as they try to dissipate heat.
During the flowering stage, the temperature is too high and can cause terpenes to evaporate. Terpenes are what give a different strain their familiar scents and tastes, so you'll want to keep them as much as possible.
To cool your grow room, switch to LED lights or improve the ventilation of the room. To make it warmer, you can use a heating pad, extra lights, or switch to the automation system.