ACF Greenhouses Blog

Beat the Heat: The Ultimate Guide to Greenhouse Cooling Solutions

2026-06-03T10:57:00-05:00

Every greenhouse owner eventually learns a tough lesson: keeping a greenhouse cool in July is significantly harder than keeping it warm in January. Because greenhouses are literally engineered to trap solar radiation, an unmanaged structure can easily turn into an oven, hitting temperatures north of 110°F that can stall growth, cause bloom drop, or wither a crop in a matter of hours.

To protect your investment, you need a multi-layered cooling strategy. Depending on your climate, your greenhouse design, and what you’re growing, the optimal setup will usually combine passive venting, mechanical airflow, and active evaporative cooling.

Here is a breakdown of the core greenhouse cooling solutions available today and how to use them together effectively.

Automated Roof & Side Vents

Passive ventilation should always be your first line of defense. It relies on natural thermodynamics—hot air naturally rises toward the peak of the greenhouse, while cooler air is drawn in through lower side vents.

How it works: Many traditional kit greenhouses come equipped with built-in roof vents.

The Upgrade: To prevent having to manually open and close vents all day, Automatic Vent Openers are an absolute necessity. These clever devices require zero electricity; they use a specialized solar-reactive wax cylinder that expands as the greenhouse heats up, physically pushing the vent open, and contracts to close it as the temperature drops.

Best For: Spring and fall temperature management, or as a baseline system for smaller hobby greenhouses in mild climates.

Mechanical Exhaust Fan Systems

When passive vents can no longer keep up with intense summer sun, you must transition to mechanical, forced-air ventilation. The goal here is simple: physically strip the hot, stale air out of the building and replace it with fresh outdoor air.

The System Components: A complete mechanical setup requires a heavy-duty Exhaust Fan mounted high on one endwall and matching Intake Shutters mounted on the opposite endwall to create a clean cross-ventilation path.

Plug-and-Play vs. Wired: For smaller or hobby setups, Packaged Plug-In Exhaust Fan Systems eliminate the need for complex electrical wiring. They plug directly into a portable digital thermostat, turning on automatically when the greenhouse hits a target temperature. For larger, multi-fan commercial layouts, Variable-Speed Wired Fan Systems give you finer control over the volume of air moved based on the season.

Pro Tip: To protect your plants from cold air shock during transitional seasons, look for variable-speed fans or add an Automated Shutter Motor to ensure intake louvers only open when the fan is actively running.

Evaporative Cooling Systems (True Temperature Reduction)

It is a hard physical law of greenhouse ventilation: standard exhaust fans can never cool the inside of a greenhouse below the outdoor ambient temperature. If it is 95°F outside, the absolute best a perfect fan system can do is keep the inside right around 95°F to 98°F.

To actually drop the temperature below the outdoor baseline, you need Evaporative Cooling.

Evaporative Air Coolers: Often called pad or swamp coolers, these self-contained units use a pump to distribute water over cooling pads while a powerful internal blower pulls hot outdoor air through them. As the water evaporates, it absorbs thermal energy from the air, discharging air into the greenhouse that can be up to 30°F cooler than the outside temperature.

Misting & Fogging Systems: A great, cost-effective alternative or supplement. By running water through high-pressure poly or PVC misting nozzles, they inject a fine mist into the air. As the microscopic droplets evaporate before hitting the foliage, the Misting Systems pull heat out of the air, raising humidity and lowering the ambient temperature simultaneously.

Shade Cloth & Covers (Stopping Heat at the Source)

The best way to cool a greenhouse is to prevent the radiant heat from getting inside in the first place.

How it works: Knitted polyethylene or reflective Aluminet Shade Cloth is draped over the exterior of the greenhouse glazing. By blocking a specific percentage of light (typically 50% to 60% for general crops), you significantly reduce the solar heat gain inside the structure.

Aluminet vs. Black Shade: While traditional Black Shade Cloth absorbs heat and radiates some of it downward, Aluminet acts like a mirror, reflecting twisted infrared light away from the greenhouse entirely for maximum cooling efficiency.

Putting It All Together

For the ultimate summer cooling setup, these systems should work like a team. By layering your defenses, you can maintain a perfect, stress-free growing environment all year long.

Setup automated ventilation utilizing roof vents or an exhaust fan system
Block dangerous sun damage with a shade cloth
Provide constant air circulation in the greenhouse with circulation fans
Add evaporative cooling if needed to drop incoming temperatures with a misting system or evaporative cooler

Ready to equip your greenhouse? If you aren't sure which combination fits your goals, try out our online Greenhouse Exhaust Fan & Cooler CFM Calculator to get accurate equipment recommendations tailored to your exact structure size.

Automatic Ventilation for High Tunnel Greenhouses

2020-03-17T10:55:00-05:00

First let's explain the differences in the various types of growing structures including: high tunnel, cold frame, and greenhouse.

Cold frames are the smallest and simplest structures for protecting plants. They are generally low to the ground and don't use any equipment other than having vents or a roll-up cover that can be operated manually. These structures are used for frost protection of plants, extending the growing season a few weeks, and/or assisting in hardening off crops.

A growing structure that integrates heating and cooling systems and can be used to grow plants throughout the year is known as a greenhouse or hothouse. The design and construction of these is more substantial because of permanent electrical, plumbing, heating, and cooling equipment that is needed for their use.

High tunnels fall into the middle. They are taller and larger than cold frames like greenhouses are, but they are designed for season extending like cold frames and generally do not have automated heating and cooling equipment. Most high tunnels come with manual roll-up sides for ventilation. This type of natural ventilation does a very good job of keeping greenhouse temperatures in check as well when outside temperatures are warm and the sides can just be left down most of the day. It is not ideal as the sole means of ventilation though. As many growers have found out, the main issue is that it is difficult to regulate temperature with this system in colder weather and staged automation can be quite expensive. This is where supplemental ventilation comes in. By adding a small exhaust fan system to the high tunnel, you can have automated ventilation and cooling in colder weather where rolling the sides down will bring the temperature down too quickly and assist with ventilation when opening the side vents is needed. The fan system can also help lower the humidity level in the high tunnel to eliminate condensation. Since the roll-up sides will handle majority of the ventilation needs as outside temperatures increase, the fan will only need to provide a fraction (Usually around 1/3 to 1/5) of the CFM air flow required if it were the only means of ventilation. A 24" or smaller exhaust fan will be ideal for most high tunnels. Add an intake shutter for the other end and a thermostat, and you have a completely automated system. We offer several fan system options with the most popular being our Basic Plug-in Exhaust Fan System which does not require wiring. We also offer premium plug-in and wired exhaust fan systems as well.

Adding Automatic Vent Openers to your Greenhouse

2020-03-02T15:31:00-06:00

Most backyard hobby greenhouse kits come with built in roof vents for ventilation / cooling of the greenhouse. These work pretty well for most areas if sized properly by the manufacturer. Roof vent windows allow hot air inside the greenhouse to escape out while cooler fresh air from outside the greenhouse flows in to replace it. These greenhouses typically only come with manual openers for the vents, but they are easy to upgrade with automatic vent openers. These openers are cheap to add and simple to install in most instances. Automating your greenhouse kit's cooling system is one of the most recommended upgrades and adding automatic vent openers is cheap, and they are simple to install in most instances as well. ACF Greenhouses offers several different automatic vent openers.

Watch a Video of an Automatic Vent Opener in Action

How does an Automatic Greenhouse Vent Opener Work?
These are often referred to as solar power vent openers because they do require any electricity to work. Instead a force called hydraulic pressure creates the opening and closing of the openers. A strong metal tube contains a mineral wax which expands with heat. This pushes the piston inside it outwards which opens the auto vent. As the temperature drops, the wax shrinks and a strong spring closes the vent and resets the piston. Most automatic openers have adjustable opening and closing temperature ranges which allows you to fine tune them to your greenhouse kit.

How do I Know Which Vent Opener to get for my Greenhouse Kit?
Some automatic openers work better than others for different applications. For instance, Univent openers have unique a quick disconnect feature which makes them ideal for cold frames and most any vent that you want to be able to quickly open and/or close the vent manually without having to remove the opener. If you live in a really windy area or want to automate a vertical hinged vent (also referred to as a side or end wall vent), Bayliss triple spring openers are recommended because of their superior wind resistance and closing strength. Lastly, there is the Gigavent for large heavy vent windows. They can lift up to 65 lbs. and have a unique built-in damper to keep an extreme wind gust from blowing an attached vent window open.

How do I Know I am Getting a Quality Automatic Vent Opener?
Hydraulic automatic vent openers were invented in Europe, home to the two most respected manufacturers in the world, Bayliss Autovents & J. Orbesen Teknik ApS. They are both well known for producing the best quality vent openers which are made to last, which is why ACF Greenhouses only offers their products. We have tested many copies from China and other regions which look very similar, but the quality is just not the same. They typically are made with thinner and cheaper materials and the power cylinders tend to fail in the first few months of operation instead of lasting for several years like their European counterparts.