Quick answer: A membrane vent (breather vent) equalises pressure between a sealed enclosure and the outside while blocking liquid water and dust. That stops temperature swings from sucking water in through seals and lets some moisture escape, so it often reduces condensation. But it is not a dehumidifier: water vapour passes both ways, and on humid days or in cold, humid climates the air inside still reaches the dew point on cold surfaces. Use membrane vents for pressure control and protection; add a cabinet heater or dehumidifier where condensation must be prevented.
Quick answer
- Vents equalise pressure and block liquid water and dust.
- They let vapour pass, so humid outside air still reaches the inside.
- For guaranteed dry conditions, combine with active moisture control.
What a membrane vent does
| Function | Effect |
|---|---|
| Pressure equalisation | Stops the enclosure "breathing" through door seals and glands as it heats and cools, which otherwise pulls in humid air and water |
| Liquid-water protection | Blocks rain and spray (rated by its IP level) |
| Dust protection | Blocks particles |
| Vapour transmission | Lets water vapour pass in both directions, so the inside can dry when outside air is drier |
Why condensation can still happen
- When outside air is humid, vapour passes in through the vent, and the inside humidity follows the outside.
- At night, cold walls inside the enclosure fall below the dew point, and water forms on them.
- Internal moisture (wet insulation, hygroscopic materials) is released inside.
- A vent's liquid-water rating says nothing about vapour blocking; it is designed to let vapour through.
Giving each method a job
| Method | Job |
|---|---|
| Membrane vent | Pressure equalisation; liquid and dust protection |
| Sealing (gaskets, glands) | Stop bulk air leaks |
| Anti-condensation heater | Keep surfaces above dew point on cold nights |
| Cabinet dehumidifier | Remove water and lower the dew point; drain it out |
| Drain vent at the lowest point | Let any liquid water out |
Compare heater and dehumidifier options in enclosure heater vs dehumidifier and see why IP-rated enclosures still condense.
Specifying a vent
- Airflow rating for the enclosure volume and expected temperature swings.
- IP rating for liquid water and dust.
- Chemical and UV resistance for the site.
- Mounting position: usually low or on the side, protected from direct spray.
- Combined with a drain at the lowest point if water can enter.
When to add a dehumidifier
- Coastal, tropical or wastewater sites with high outdoor humidity.
- Cabinets with large day–night temperature swings.
- Cabinets housing electronics sensitive to corrosion.
- Where condensation has already been seen.
See our electrical cabinet dehumidifiers.
FAQ
Frequently asked questions
Do breather vents prevent condensation?
They reduce it by stopping pressure-driven breathing, but they do not remove moisture. Humid outside air still enters as vapour.
Where should a membrane vent be installed?
Usually low or on the side of the enclosure, protected from direct spray, often paired with a drain at the lowest point.
Can I use a membrane vent and a dehumidifier together?
Yes. The vent handles pressure; the dehumidifier handles moisture.
Sources
- IEC 60529, Degrees of protection provided by enclosures (IP code).
- ASHRAE Handbook—Fundamentals, Psychrometrics.
