Greenhouse Ventilation

Greenhouse Ventilation

Greenhouse Ventilation

Greenhouses without proper ventilation can quickly become inhospitable and impossible to grow crops efficiently. Most greenhouse kits being sold today are lacking sufficient ventilation necessary to produce the best crop possible.

Importance of Greenhouse Ventilation

Greenhouse ventilation plays an important role to plant health and a grower’s success. New greenhouse gardeners overlook ventilation when deciding on which greenhouse kit they should purchase. A majority of kits being sold today are under-ventilated which ultimately contributes to slow growth, poor yields, and problems with fungal pathogens. A properly ventilated greenhouse will be able to maintain the environmental conditions necessary to allow plants to maximize photosynthesis, uptake nutrients, and produce flowers.

Sunglo Greenhouse Series 10

The Basics of Greenhouse Ventilation

Greenhouses need to have the ability to breathe and exchange their inside air with fresh outside air.  This is accomplished by intaking air through vents while at the same time allowing air to escape through an exhaust vent.  When all the original air has been exchanged within a greenhouse with fresh outside air this is referred to as one air exchange.  Ideally, a greenhouse at a minimum needs to have one air exchange every minute when it is experiencing hot sunny conditions during summer.  With this rate of air exchange, you hopefully can provide the best environments for your plants by keeping temperatures down and replenishing carbon dioxide for photosynthesis.

Two types of Ventilation

There are two types of systems used to ventilate a greenhouse. The first is passive ventilation. Passively venting a greenhouse uses vents and openings in the structure. The idea here is that air will naturally enter and leave through these openings. A typical design will place vents in the peak and/or ridge of the greenhouse and as hot air rises it will escape and be replaced by fresh air.

Sunglo Greenhouse Ridge Vent

This is taking advantage of that fact cooler air sinks while hot air rises, convection. These roof and ridge vents are opened either manually or automated with wax cylinders.

To make this truly effective you need to have intake vent(s) low on the greenhouse walls with the ridge vents approximately 10 feet above. Most passive systems require wind speeds of somewhere between two and three miles per hour to provide the required ventilation.  A greenhouse design may consider the door opening or even have side walls that open as part of the ventilation system. The great thing about venting your greenhouse in this manner is the low cost and no electricity needed to power equipment. The downside is it’s not very effective as you have no control over the system and sometimes it will work and other times it won’t.

The second type is active ventilation. This ventilation uses powered mechanical devices like exhaust fans. The fans force the air exchange to happen at a predetermined temperature. Using a greenhouse exhaust fan allows the grower to have control over the greenhouse environment. These fans can be programmed with a thermostat and/or timer.

Exhaust Fan inside a Sunglo Greenhouse

Exhaust fans are typically placed slightly above the plant canopy or at mid-height in the greenhouse Again intake vents can be placed down low or at an equal height to the exhaust fan. The downside here is that it requires electricity and fans cost money.

An efficient greenhouse design will incorporate both passive and active ventilation. Having both will allow the grower the most control over the greenhouse environment meeting your plant’s needs.

Solar Powered Greenhouse Fan

I thought it worth discussing solar fans and their use in greenhouse ventilation. The solar-powered fans for greenhouse ventilation have become more available these days and are offered as part of the greenhouse kit or as an additional accessory. On its surface, these fans seem like a brilliant idea because they don’t require you to run electrical out to the greenhouse.

Solar Powered Attic Fan -Photo by Active Ventilation

I want to address a few concerns regarding their use in a greenhouse design. Most solar-powered greenhouse fans are installed on the roof and will therefore reduce the amount of light entering the greenhouse.  Another key point is these fans are not very powerful and do not produce enough airflow (CFM) to adequately vent the greenhouse. If you are considering using a solar-powered greenhouse fan for your ventilation I suggest purchasing a larger fan than what I see currently being sold with greenhouse kits. The fans will need to be quite large to be effective and unfortunately cost more than a comparable greenhouse exhaust fan.

How Much Ventilation Do I Need

Okay, my greenhouse needs to have ventilation and is recommended to have at least one air exchange every minute.  When considering purchasing a greenhouse you should calculate the total cubic feet of air volume inside your greenhouse which will help determine the ventilation required.  The manufacturer should be able to provide you with that information as well.  There are many online calculators to help you with that math as well.  You will need to know the length x width x height of your greenhouse.  Once you know your greenhouse’s total volume then that is the amount of CFM that needs to be exchanged every minute.  If the greenhouse ventilation design is completely passive it makes that challenging to determine.   I would suggest more vents and openings the better.  For the exhaust fans, you’ll want to refer to the technical specifications which will list the CFM rating.  The idea here is to install a fan with a slightly higher CFM rating than your greenhouse or install two smaller fans.  It is also important to make sure there are intake vents in the greenhouse. 

Backyard Greenhouse Kits

The truth is the majority of greenhouse kits offered on the market today are under-ventilated. Either they are relying strictly on passive venting as a strategy or simply do not have enough ventilation openings to keep the greenhouse environment from getting uncomfortable and creating difficulty for your plants. Most manufacturers don’t even put much emphasis on ventilation. As an experienced greenhouse grower, I highly suggest purchasing a greenhouse kit that includes a greenhouse exhaust fan and thermostat control that has been sized for the greenhouse you are purchasing.

Our Sunglo Greenhouses have been specifically designed for proper ventilation. We incorporate both passive and active ventilation in our greenhouse kits. A Sunglo Greenhouse comes standard with a 16” intake louvered vent, operational door vents in the peak of the greenhouse, an extra tall front door with an openable screened window, and a 16” greenhouse exhaust fan with aluminum shutters rated at 1,289 CFM with digital temperature control. Our competitors cannot match our ventilation performance. We understand these features add additional cost to our greenhouse kits but we want to provide you with the best greenhouse possible.


Take your growing to a new level with Sunglo Greenhouse.   

To speak with a Sunglo Owner who has experience growing in a Sunglo Greenhouse at  720-443-6711.

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