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Cultural Healing and Life

The Indoor Garden Environment - Part 5 - Ventilation & Calculators

JJ the Gardener

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The Indoor Garden Environment

~A Cultural Healing and Life Compilation and Writing.





Ventilation is a big part of creating and managing the entire environment.  First we need to understand the needs of the plants being grown.  A wise gardener can not only create a stable grow environment but can manage with accuracy the environment in regards to temperature, humidity, CO2 and air quality.  Their are a variety of setup and options that offers a range of  capabilities depending on a gardens needs. 

  • Understanding how to use these tools is vital in creating optimized grow areas.  What ventilation tool works in one setup may not be ideal in another ventilation setup. 
    • For example, dealing with humidity is different in a tropical area compared to dry climate area. 

Often people will be told that one method may not be good when in fact that method may be most beneficial in certain situations.  This aspect negatively works against us by instilling these misunderstood views.  Creating an effect that limits the typical ill informed gardener in knowledge and capability in respect to options to utilize to manage their garden. 

  • This may in part be due to much of the communities knowledge coming from marketed directions and forums, never mind this one :33zzold:



Ventilation Types

  • Active or Passive Ventilation.
    • Active Ventilation - Using a slightly smaller inline fan to intake fresh air into your grow room.
      • This has less strain on your garden's extraction fan and is more efficient.
        • Exhaust fan typically will have a filter attached
          • This reduced effectiveness of the fan.
            • Making it sensible for a lower intake fan.
            • Using fans with control switches can give you better control.
      • I tend to recommend that if a grower can afford and if they plan to expand at a later date to over spec the requirements using a speed controller for the fan to adjust to correct CFM rate for the grow.
        • For tents
          • I do not recommend a weaker intake fan rated CFM for tent size as negative pressure is a problem on stitching.
        • I do not recommend an overly strong intake fan rated significantly higher than your CFM needs as a whole. 
          • Consider for intake fan, the next fan size or model down from your intake fan. 
            • Adjust for exhaust filter and ducting losses.
              • Intake is 8 inch fan with dimmer switch and an 8 inch exhaust fan with/without dimmer switch.
              • Intake is 6 inch fan with a 8 inch exhaust fan.
              • Intake is 4 inch fan with a 6 inch exhaust fan.
      • Negative of too much ventilation is high heat, high humidity and low levels of CO2, this will negatively affect photosynthesis.
      • Negative of too little ventilation is low humidity and stomata/transpiration issues.
        • Illustrates traits often associated with genetic aspect when in fact it is a result of a plant responding to environmental stress that the gardener may or may not appreciate.
        • Extreme situations of low humidity will put the plant in a hibernation or pause state until the environmental stress passes (humidity levels return to functional levels).
          • Dry climate areas with low humidity are higher risk.


  • Passive ventilation - I dislike this typically due to the following.
    • Basically is a low vent on one side and a high vent on the opposite side of the room or tent.
    • Works best during colder periods when the difference between inside and outside temperatures is greatest.
      • Passive ventilation used alone can’t extract humidity.



Determining Ventilation Requirements

  • Cubic Foot per Minute of ventilation requirement is needed.
    • Exchange your garden's air at least once per minute at minimum.
      • Not as important in vegetative growth when plants are small as they have less leaves.
      • "Best Practice" is to exchange once per minute.
        • Ensure fresh air intakes are managed (intake filter) for bugs and pest that could enter the garden via this pathway.
          • Intake filter will reduce approximately CFM's by 25%
          • Bends in ducting reduce CFM's drastically.
            • Ducting curved 30 degrees reduces CFMs by 15%
          • Air quality - Low humidity intake air will need less ventilation until humidity is correct as the leaves will begin lose moisture and negatively affect the stomata and the photosynthesis process.


  • To calculate initial cubic feet per minute of ventilation you need, start with calculating the size of the garden in cubic feet. You do this by multiplying the height, length, and width of the room.  



Ventilation Summary

Understanding ventilation and how to use it in various situations is a skill that few appreciate and with automation capabilities it becomes rarer still.  Often their are negative garden issues associated with to little ventilation within a multi ventilation setup and when this occurs it can lead to potential harmful situations like mold or heat aspects.  It is important to understand ventilation but one can make it as complex or as  simple as they wish.  The point is that now one can make an informed decision and have some direction on how to effectively setup for each perspective gardeners needs.




Environment the Tool and some tools

The environment is the driving factor in a garden and as such it is wise to utilize this to our advantage rather than to just build around it.  As an example, this is a common practice done by to instigating the flowering stage by adjusting the timing of the lights to further adjustments in temperature and humidity depending on how simple or as complex the design of the garden and needs of the crop are.

Understanding how to use the tools such as ventilation and the different setups that enable various capabilities that may offer solutions to gardeners with certain situations and/or needs.  Further still this knowledge gives you the capability to adjust to environmental conditions experienced out of normal weather patterns. 

  • The key is to appreciate that assisting a plant through a stressful period of time be it normal growth period development and/or environmental based stress that addressing the plant at all levels from environmental aspects to nutritional aspects as to ensure the overall health of the plants is strong. 
  • A gardener must not depend on the strength of any one aspect to cover for not being competent in other areas of plant care such as heat control but not humidity and also take into consideration nutritional and plant physiology aspects for before during and after the stress event.


Some environmental control aspects.

  • Hot and Cold areas
    • Sealed Room Consideration (higher electrical cost but is easier to control grow environment)
      • Air conditioning aspects
        • Air conditioning
        • Air cooled reflector hoods
          • Insulated ducting
      • Carbon dioxide
        • Burner.
        • Bottled.
        • Bucket/Bag grow shop kits
        • Wine/Ethanol making.
      • Air Filters
        • Pest control
        • Air quality and smell controls.
      • When seasonal outdoor temperatures are not good.
        • Air intake from inside the building offers stable temperatures and humidity levels.
          • Use an Lung room or tent to temper and treat air before going into garden area.
            • Hot areas
              • Outside air intake into an active cooling lung room.
                • Balance for proper humidity level and temperature.
            • Cold areas intake into an lung room.
              • Outside air intake into lung room.
              • Grow room exhaust into lung room
                • lower temperature and exhaust or intake into grow room as best for your setup.
                  • If exhaust to outside this helps remove aspects of ice build up.
                  • If exhaust to grow room ensure proper temperature and humidity levels for current growth cycle.
          • Lung room option 2
            • Intake air from inside building to lung room (stabilized but not ideal)
            • Cool or heat lung room and obtain proper humidity level
            • Exhaust lung room into grow area.
            • Exhaust grow area outside (filtered most often)
              • Exhaust grow area inside of building (Use the heat) or
              • Exhaust grow area to a lung room for temper for outside temperatures.

The biggest thing is to make informed and calculated decisions when working an issue.  Their is no need to panic and rush into a decision that make things worse.  Gain control of the situation and sit back and look at it through eyes as if you was going to give advice to another.  Try to see the garden as if for the first time and go over your grow history and analyze.  The answer or the answers are their.

When you can during stressful climate times and periods, go for nature walks and see what plants are doing well and see if get any ideas! 


Video on Heat in the grow room


Video on cold in the grow room


Fan controller video


AC video


Air Cooled Hoods & Ducting Video


Filter size video


Additonal tools


  • Click Hortilux logo for Watts/lights to BTU calculator
  • A BTU, also known as a British Thermal Unit, is a measurement of the energy needed to cool a substance. Grow lamps generate a lot of heat. By converting your wattage into BTU per hour, you’ll have the information you need to keep your plants cooled so that they don’t burn up from the heat of the grow lamps.
  • A BTU is also the equivalent of 252 heat calories, not to be confused with the kilo-calories of food, and of approximately a third of a watt of electrical power. When speaking of cooling power, the BTU also works in reverse.
  • The air-cooling power of an air conditioning system refers to the amount of thermal energy removed from an area. Hence a 65,000 BTU heater and a 65,000 BTU air conditioner are of roughly the same capacity and size. The higher the BTU output, the more powerful the heating or cooling system.
  • The thermal energy needed to raise water one degree Fahrenheit can depend on the original temperature and the method used for heating. Therefore, it is possible to get several different definitions of a BTU from different sources. This rarely has a palpable effect on consumer product information, however.


Click for Phresh CFM, Cubic Feet per Minute Calculator


Click for Phresh CFM Calculator



Indoor Garden Environment Summary

Ok, by controlling the environment we can affect plant physiology and development stages but as we know their is no simple "one size fits all" formula for managing the indoor garden. 

By understanding to appreciation the aspects discussed in this writing you have created a base of knowledge that will allow to address virtually all the varied aspects of the environment and how to control them to serve the plants and you very well.  By making a true home for our plants, they will truly it make it that and live their life healthy and fit.

  • Always understand via competent analysis of established to new technology that can affect indoor environments.
  • Continue to learn on plant physiology.  Always be the student.
  • Continue to learn on plant and environment interactions and aspects.  Always be the student.

It is not so important that any specific method be strictly followed as that you have a true understanding of all things affected and then from that knowledge you apply effective methods to obtain the conditions you want. 



For You





When environmental and plant physiology wisdom is effectively gained it can become the advantage that can equal or best the long established or it can just be what makes a garden happy and productive. 

~JJ The Gardener


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