One of the biggest questions our clients face in the design and construction of a cultivation facility concerns the HVAC system and which type of system choices will provide the most efficiency, potential for scaling the operation up and be the best financial option to meet the facility’s needs now and later. This is an especially important consideration in Michigan, where we have the joy of four true weather seasons every year, but also the challenges of maintaining as close to a homeostatic environment as possible to ensure that the agriculture being produced is consistent, manageable and does not yield unwanted results as the end of the maturation cycle in all seasons.

Five primary considerations to gauge when engaged in pre-planning phases of the facility are paramount to how much return on investment you can expect to derive from a harvest. These include temperature, humidity, pests, CO2 levels and airflow.

Temperature is an obvious component.

To have consistent product, you have to maintain consistent temperatures inside your cultivation facility. This cannot be overstated, given the extreme temperatures present here in Michigan throughout the year. Whichever HVAC system is purchased for your grow, your paramount concern should be the system’s ability to maintain temperature levels for the different stages of growing, despite what havoc Mother Nature might be delivering outside the facility. Keeping temperature within certain acceptable ranges, or bands, ensures a consistent product. The reason HVAC systems are key to keeping temperature controlled is obvious, but what may not be obvious is which of the systems you are considering will be able to deliver the tight temperature controls you desire in a closed, sealed environment as to not allow outside variables to encroach upon the indoor grow environment.


A key metric to analyze when determining appropriate temperature is the type of lighting system your facility intends to use.

Lighting is, generally, the most energy-consuming component to any indoor cultivation facility. The type of lighting system to use becomes a critical choice for flowering and plant growth. Once the agriculture is flowering, the plant is sending an open invite to molds, fungus and mildew, all of which must be prevented with appropriate controls. As a result, the lights need to be at intense levels during this stage so as to control humidity levels that do not open the doors for the three uglies mentioned above to infect, overtake and kill your turn cycle. The other three large energy consumers in an indoor grow facility are cooling, dehumidification and your ventilation system. All told, these four considerations can easily equate to up to fifty percent of your total overall energy consumption. There are ways to chip away at this percentage, but nothing can alleviate the large portion of costs these four categories deduct from your bottom-line costs to run your facility.


Humidity control is crucial.

No surprise here, as we discussed above with mold, fungus and mildew. What is a surprise is how humid it will be during certain times of the year in Michigan. Be sure and check out the weather data for the location where your grow facility is going to be located. Inside the facility, humidity is arguable the most crucial consideration. If your facility is too humid, this is an open invitation for fungus, diseases and potentially total failure in a growth cycle. On the other hand, if your grow environment is too dry and arid, your plants may endure being too dry and worse heat stressed. When evaluating HVAC systems in relation to humidity levels, you must consider temperature and humidity as one package. Why so, you may ask? In allowing higher room temperatures and weighing humidity levels, your grow room can have higher humidity due to the increased temperature. The higher temperature and humidity standards you have, the less capacity you need from your HVAC system upfront. Conversely, the lower the temperature is and the lower the humidity in your facility, the more advanced your choice of dehumidification system needs to be to maintain chilling under the dew point of the room. This leads to lower costs up front in your initial investment for an HVAC system, which includes both cooling capacity and dehumidification. Weighing these considerations allows you to set up lower front costs for both the system you choose and your utility bills.

When evaluating dehumidification options, always opt for the most efficient option energy wise. Why do we give this advice to clients? This offers huge reductions in energy bills. A ten percent cost reduction based on the most energy-efficient system that your operation can afford and easily yield a savings of over ten percent. One of the most common types of dehumidification systems widely used are refrigerant based. Airconditioning systems and chilled-water systems also serve as dehumidifiers. Chilled water systems are a component we ask our clients to give strong consideration to, as these allow even more energy savings to your bottom line than the standard or split air conditioning units available in the marketplace. The beautiful feature of using a chilled water system is the facility operator’s ability to reduce the speed of the fan and lower the water temperature to obtain higher levels of heat removal. Basically, a chilled water system allows more control over the levels of humidity in the grow while lights are on without having to use any additional equipment, such as a separate dehumidifier.


Let’s talk about the three uglies, also known as pests: namely, mold, fungus and mildew.

Operationally speaking, you always want to consider ways to annihilate creating habitats where mold and pests can hide. We advise clients to keep duct work out of the actual grow space, as ducts are wonderfully dark, wet places for enemies to hide. Eliminating duct work from the actual grow room is not a viable option, but you can place air-handling equipment in the room to circumvent infestations.


The next consideration to consider in planning, designing and operating a cultivation facility is your CO2 levels.

How can this level be optimized, while keeping energy costs under control? Multiple air handlers is the short answer. Again, your facility plan may only include a plan for one enormous air handler that transports all the HVAC produced air into one grow room through the duct work. Ask yourself this: What happens if that one and only air handler fails? Chances are, this failure will cause your operation to lose that entire room’s crop. When a facility has multiple air handlers, if one fails, all is not lost as there are backups still working and the air handlers that are operational can carry the crop through to its harvest. At harvest, you can have the failed air handler fixed or replaced depending on the cause of the failure.

Hunter Green encourages cultivation facilities to weigh the benefits of a split ductless A/C, heat pump unit. Why? Because, this type of system allows for separate and energy efficient dehumidification in your grow rooms. There is a general belief in the industry that utilizing multiple-split units leads to more energy efficiency and less costly options for small grows, as opposed to rooftop systems. Hunter Green defines smaller grows as being under 10,000 square feet. As rooftop systems are often used, you may be asking yourself why? The simple answer is ratings regarding the efficiency of the units being used. A SEER rating gauges energy efficiency. The basement rating of 13 is the minimum standard for air conditioning units. Most of today’s units available in the marketplace range from 13-21. There are systems available in the range of 14 to 25 and higher SEER. The higher the SEER number assigned to an air conditioning unit, the higher energy efficiency the system will yield. The average rooftop HVAC system has a SEER rating of 14 to 15, whereas there are split ductless heat air conditioning units available that carry SEER ratings of 25. This differential can really cut into your bottom line. Of course, you will also need to weight the size of your cultivation facility and whether chilled water system or hot gas heating systems or the split ductless air conditioning and heating pump systems will match your needs, as the split systems mandate a facility manager who is well-versed in operating and maintaining these in tandem with separate dehumidification units. The larger your grow, the more you will want to direct your attention to rooftop models. If you employee a rooftop unit, consider having additional dehumidifier units installed in the flower rooms so that cooling and dehumidification efforts are less costly.

Speaking of hot gas forced air systems, keep in mind that this type of unit requires an extra condenser coil to reheat when needed. Practically speaking, this type of setup adds an additional layer in the form of a condensing coil to work in tandem with the reheat coil. However, these additional layers also allow for you to push heat out of the grow and outside when cooling is required inside (i.e. when the lights are on). On the other end of spectrum, when you do not need the lights on, you have the ability to utilize the other condenser coil for reheat when your grow room has less cooling needs. Everything is a balance.

Always consider what your cultivation facility really needs, not what you really want. As I always remind my children, there are two classes of people: the providers and the consumers. As parents, we serve as providers to the consumers; our children. Often times when you evaluate what you need versus what you would like, you will reach the conclusion that what you really want will cost you far more than what you really need to maintain consistent, manageable and fruitful results. The HVAC system you choose can make or break your indoor cultivation facility, so choose carefully and only after you  and your team conduct extensive research. One last thought: go into the design and selection process with the vision of what you ultimately want to accomplish when you scale your operations up.

Useful resources: To calculate dew point, use an online calculator.