What is a wet wall?
Wet walls are greenhouse cooling systems made up of cooling pads housed within an aluminium frame. Water is pumped through the wall, while a fan on the opposite side pulls air across the wet pads. As the water evaporates, it cools the air before it circulates through the growing environment.
The water is collected, filtered, and recirculated, allowing the system to cool continuously. Because wet walls introduce high moisture levels, the underlying greenhouse structure must be protected from damage. Plastic sheeting is often used as a base layer to prevent moisture issues. Additional fabric layers may also be added to help support plants while retaining moisture from the wet wall system. 
6 facts about greenhouse wet walls
1. Wet walls work best in hot, dry climates
Wet walls are most effective when humidity levels are low. They’re commonly used in hot climates such as Australia and the southwestern United States, where evaporative cooling can significantly reduce greenhouse temperatures.
2. Wet walls use a honeycomb-style cooling pad
The cooling pads typically feature a honeycomb structure made from cellulose material. This design allows air to pass evenly across the wet surface while reducing degradation and minimising moss build-up.
3. Water is continuously filtered and reused
Water trickles from a gutter at the top of the wall and flows down into a collection pipe. From there, it passes through a filtration system before being recirculated. This makes wet walls an efficient and relatively water-conscious cooling method.
4. Wet walls are commonly paired with extraction fans
Wet walls are usually installed on one side of the greenhouse, with extraction fans positioned on the opposite side. The fans pull air through the wet pads, creating a cooling effect that can reduce temperatures by 10–15 degrees.
5. Wet walls can be part of a hybrid cooling system
In extremely hot conditions, growers may use wet walls during the day and switch to natural ventilation or passive airflow in the evening. This approach helps manage temperature while reducing unnecessary humidity overnight.
6. Wet walls are typically used in large commercial greenhouses
Due to the cost and complexity of installation, wet walls are most common in large commercial operations. The system requires permanent plumbing and a carefully planned setup. While the initial investment is higher, wet walls can be a highly effective long-term cooling solution.
Cooling your greenhouse
Controlling temperature and humidity is essential for maintaining healthy crops. While wet walls are a proven solution for large commercial greenhouses, they’re not the only option.
Ventilation and airflow play a critical role in removing excess heat and moisture from the growing space. The most effective cooling approach depends on several factors, including greenhouse size, regional climate, crop type, and budget. In many cases, cooling methods work best when they’re used together rather than in isolation.
Related greenhouse climate topics
Wet walls are just one way to manage greenhouse temperature and humidity. You may also find these guides useful:
In commercial greenhouses, cooling decisions work best when they’re backed by consistent data. Bluelab supports growers by helping them monitor the conditions that affect crop performance, especially when temperature and humidity shift quickly with evaporative cooling systems.
Contact Bluelab to discuss monitoring and measurement options for your grow environment.
