HVAC and Cannabis

Whether you're working with an open-air system or a closed one, maintaining proper temperatures is crucial. For the most part, plants prefer a sweet spot of 75-80F when the lights are blaring, and 68-75F when they're not. If it's too hot - above 80F or so - plants are using their energy to stay cool, instead of using it to grow larger or produce flowers. At 95F, photosynthesis stops completely. If it's too cool - anywhere below 60F - the plant's metabolism slows down, as does photosynthesis. If temperatures drop to 40F, you risk tissue damage. Ideal temperatures depend on a few factors. Lights are the biggest culprit, but you should account for ballasts and fan motors as well.

Finding the right humidity for your garden is something of a balancing act: too much, you risk exposing your plants to mold and rot, you also discourage the rate of transpiration, which can stuntyour plants. But not enough and you risk drying out the foliage, which likewise discourages growth. As with temperature, the optimal relative humidity varies based on where your plants are in their grow cycle. Cannabis does best starting around 80% relative humidity, then gradually lowering it to as low as 40% when flowering. A well-engineered HVAC system must respond quickly and accurately to your desired conditions.

Along with light, plants need water and carbon dioxide to create energy. The concentration of carbon dioxide in Earth's atmosphere is currently around 400 parts per million, and is on the rise. When growing, the more carbon dioxide plants absorb, the more mass they can create. This means faster growth and more robust plants. If you're using an open-air system, the natural levels of carbon dioxide will likely suffice, assuming there is sufficient aeration. If you're using a closed-air system, you'll need to provide it.

Air must constantly be moving in a grow room to deliver needed carbon dioxide to the plants, and to remove "unwanted" oxygen and water from them. Maintaining proper airflow is also important for temperature and humidity issues, since moist, stagnant air is an invitation to mold and disease.

The quality of air filter needed does depend on where you grow. Gardens in big cities or near highways, for example, may have greater requirements. A good air filter helps capture larger particles like dust and sediment, which keeps them off the plants' leaves. An often bigger issue is the sheer potency of the smell of Cannabis plants that are well cared for. Its becoming common for grows to be fined thousands of dollars for the smell drifting into neighborhoods a good distance away. Carbon filters are especially useful when it comes to dealing with odor. Fans draw air through this filter, where molecules adhere to the activated carbon. Once out the other side, odors are virtually eliminated.