Some hobby greenhouses, depending on location and desired use, will be OK with no additional equipment besides the structure itself. Many however, will need at least some additional equipment to help manage the internal environment and make it desirable to growing plants (or relaxing people). The most common addition to a backyard greenhouse will be a heater. We've already covered sizing a heater, and the most common heater for a small to medium sized hobby greenhouse is just a simple electric heater.

The next most important system in a greenhouse is ventilation and cooling. Proper ventilation is important because it helps cool your greenhouse by allowing fresh air in to replace hot, stagnant air. This can be accomplished passively (naturally) in most of our small hobby greenhouses since typically they are already equipped with either roof or sidewall vents. This, in addition to opening the door, may be enough for proper ventilation.

Slightly larger houses may need to step up to a fan and shutter system. The fan(s) and shutter(s) are sized to exhaust the volume of air in the building within a minute, a measurement commonly called CFM (cubic feet per minute). One drawback to both of these systems is that the internal temperature of the building can only match the external temperature.

If you would like to actually lower the temperature in your greenhouse below the external temperature, you will need to step up to some form of evaporative cooling. Typically, this is a solution only necessary in larger hobby greenhouses. Additionally, you can increase the efficiency of any cooling solution with a shade cloth, which helps lower temperatures by blocking a certain percentage of light from entering the building.

Posted below are several illustrations designed to help illustrate how each of these methods works.

NO COOLING
1.With an outside temperature 95°F the inside temperature of greenhouse can exceed 140 °F.

2. Plants will die within a short period of time.

NATURAL VENTILATION
1. Roof vent opens to allow hot air to escape to outside.

2. Door or other opening must be left open to provide for incoming air from outside to replace exhausted air.

3. On hot summer days temperatures can rise 20 to 30 degrees above outside temperature.

4. Recommended for mild climate areas only.

FAN & SHUTTER COOLING
1. Outdoor air is introduced through motorized inlet shutters.

2. Hot air is exhausted by exhaust fans.

3. Temperature inside house can be maintained within 10 degrees of outdoor temperature with properly designed system.

4. Fans and shutters are controlled by thermostat.

  FAN & SHUTTER COOLING WITH SHADE CLOTH
1. Outdoor air is introduced through motorized inlet shutters.

2. Hot air is exhausted by exhaust fans.

3. Shade cloth is placed over exterior of greenhouse or suspended from wires placed on inside.

4. Temperature inside house can be maintained within 3 to 4 degrees of outdoor temperature with properly designed system.

5. Fans and shutters are controlled by thermostat.

EVAPORATIVE COOLING (POSITIVE PRESSURE)
1. Intake air is cooled by Evaporative Cooler, usually located outside, and discharged into greenhouse. Hobby greenhouses of up to 600 sq. ft. can be cooled with a portable evaporative cooler that sits inside the greenhouse.

2. Hot air is exhausted through outlet shutters that operate automatically on pressure differential. Portable coolers do not require these shutters.

3. Temperature inside house can be as much as 10 to 15 degrees cooler than outdoor temperature with properly designed system.

4. Evaporative Cooler is controlled by thermostat.

5. System efficiency can be increased with the use of shade system. The fans will not have to work as hard to maintain the desired temperature.

  EVAPORATIVE COOLING (FAN AND PAD)
1. Outdoor air is drawn through pad cooling system located on one end wall of the greenhouse. This cool air enters into the greenhouse.

2. Hot air is exhausted by fans mounted on the opposite end wall of the greenhouse.

3. Temperature inside house can be as much as 10 to 15 degrees cooler than outdoor temperature with properly designed system.

4. Fan & Pad System is controlled by thermostat.

5. System efficiency can be increased with the use of shade system. The fans will not have to work as hard to maintain the desired temperature.