Fan vs. no fan

7 years ago

Moving ahead on my greenhouse. About 12 by 9 feet and 7 1/2 high. I have the glass, double pain. Looking at ventilation options. Do I need a fan? If no fan, is there some ratio of area to vent size that will allow convection to do the job? Anybody got a gut feel of what works? What works for you, both using just convection, and also those that ended up putting in a fan? Thanks for past help, and any comments here.

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Comments (5)

kudzu9
7 years ago
Most any greenhouse can benefit from a fan. It not only helps to control temperatures, but it also contributes to stronger stems on plants, particularly seedlings. My setup is nothing more complicated than a $30 oscillating fan attached to a shelf, and plugged in to a $50 thermostatic control that I have set to kick in above 85F.
Barrie, (Central PA, zone 6a)
7 years ago
You need to have a means of releasing excess heat that builds up quickly once sun is shining brightly. I'm not sure that you need a large exhaust fan for a smaller structure and in fact if you install too large of an exhaust fan it will be repeatedly turning on and off to keep inside temperature normal when sun is bright, yet outside air is cooler.

In many high tunnels the ventilation is accomplished by rolling up the sides of a structure. Others install solar powered ridge vents or other passive controls to release the heat. Fans have some advantages but the advantage that Kudzu mentioned is better accomplished by an internal circulation fan as opposed to a wall mounted exhaust fan. I use both fan types and still roll up sides during summer months.

If you install an exhaust fan you must allow for makeup air by either physically opening an opposing door, window or have an intake louver that is open when you either manually or thermostatically run the exhaust fan.

A simple internal circulation fan is not enough unless you otherwise open the structure. If you just circulate 120*F air inside your plants will still suffer severely.
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oakhill (zone 9A, Calif.)
7 years ago
For passive greenhouse ventilation, the top vents should be at least 20% of the floor area, and the bottom side vents at 10%. For your structure, that would be 22 sq. ft top and 11 sq. ft bottom vents.
hex2006
7 years ago
You also have to take account of the height difference between the top and bottom vents and the temperature difference.
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Advance Greenhouses
5 years ago
If you are going to use the greenhouse year round and you are in even a moderate climate you will need aventilation system. For this size I would recommend a 12" exhaust fan up high in one end, a 12" motorized intake shutter down low in the opposite end. I would wire them both to a thermostat so they come on at the same time. If you are interested in ventilating your greenhouse without electricity, here is ablog post I wrote about the different options.

Fan vs. no fan

Comments (5)

kudzu9

Barrie, (Central PA, zone 6a)

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oakhill (zone 9A, Calif.)

hex2006

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