US How condensation forms on electronics
Condensation on electronics is liquid water that forms when a surface is colder than the dew point of the air around it. The dew point is the temperature at which air, cooled at constant pressure, becomes saturated and can hold no more water vapor. Any surface below it collects droplets, whether that is a cold drink can or a circuit board.
The dew point depends on how much moisture is in the air, not on the air temperature alone. Warm, humid air has a high dew point, so even a slightly cool chassis can get wet. Dry air has a low dew point, so equipment can be quite cold before anything forms. Relative humidity describes the same thing from the other side: the closer it is to 100%, the closer the air temperature is to the dew point.
On electronics, a film of water bridges conductors, lets current leak between tracks, and starts corrosion on connectors and solder joints. Over months it can grow dendrites between pins. A single event may cause no visible damage, while repeated cycles shorten the life of a board.
Where dew point condensation is most likely
Risk is highest where cold and warm air meet, or where temperature swings every day. Look for these situations when you plan an installation.
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Cold stores and the cold chain. Equipment moving between a chiller or freezer and a warm loading bay, or mounted at the doorway between them.
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Outdoor cabinets. Enclosures cool at night, then warm, humid morning air reaches surfaces that are still cold. Metal facing a clear night sky can fall below air temperature.
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Vehicles and portable kit. A tablet or computer brought in from a cold vehicle into a warm building collects water within seconds.
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Washdown and wet processes. Hot water and steam raise the dew point of the room, so any cooler surface condenses.
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Equipment that is switched off. A computer that is off overnight loses the heat that kept it above the dew point.
Dew point at a glance
The table shows typical dew points for common conditions, calculated with the standard Magnus approximation. Any surface colder than the dew point will collect water.
| Air temperature | Relative humidity | Dew point | What it means |
|---|---|---|---|
| 20 °C | 50% | Around 9 °C | An office or heated building. Only very cold equipment is at risk. |
| 20 °C | 90% | Around 18 °C | A damp plant room. A chassis just 2 °C cooler than the air gets wet. |
| 25 °C | 70% | Around 19 °C | A loading bay in summer. Equipment brought out of a 2 °C chiller condenses at once. |
| 30 °C | 90% | Around 28 °C | A tropical or washdown area. Almost any cool surface condenses. |
| 5 °C | 90% | Around 3.5 °C | An outdoor cabinet at night. Metal that radiates heat to a clear sky drops below this. |
Datasheets usually give a humidity range such as 5 to 95% RH, non-condensing. Non-condensing means the rating assumes no water forms on the equipment, so it is a limit on the installation, not a promise the hardware can cope with liquid water.
How to prevent condensation on electronics
The aim is to keep every surface above the dew point, or to keep humid air away from the electronics. Most installations use more than one of these measures.
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Keep it running. A computer that runs continuously holds its chassis a little warmer than the air. Avoid switching off overnight in cold, humid places.
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Fit an enclosure heater. A small thermostatic or hygrostatic heater keeps the inside of a cabinet a few degrees above ambient, often enough to stay above the dew point.
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Seal and vent. A sealed enclosure with a pressure-equalising breather vent lets the box breathe through a membrane that passes air and vapor but blocks liquid water.
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Control the humidity inside. Desiccant packs absorb moisture in a sealed box. They saturate over time, so they need checking or replacing.
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Acclimatise cold equipment. Leave equipment in its bag or case while it warms up, so condensation forms on the packaging, not the boards.
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Coat the boards. Conformal coating protects against moisture that does form.
Sealed or vented enclosures
A higher IP rating keeps rain and hose water out, but it does not stop condensation. Air trapped inside a sealed box still carries moisture, and when the box cools that moisture condenses on the inside walls and boards. A fully sealed box can also pump moist air in as it heats and cools, through seals that wear over time.
A good outdoor design combines a sealed enclosure, for example one of our IP66 computers, with a breather vent, a heat source and a drain point at the lowest corner. Our guide to designing outdoor computer enclosures covers venting, sun loading and cable entry in more detail. Inside a cabinet, keep cables entering from below so water cannot run along them to the connectors.
Condensation and fanless computers
Fanless computers suit humid and cold sites because they have no vents drawing outside air across the boards. Their sealed metal chassis acts as the heatsink, so it stays a few degrees warmer than the air while the system runs. Systems from our wide temperature computers range are also specified to cold-start at low temperatures, so they can be left running where a commercial PC would be switched off.
For cold-chain sites, the riskiest point is the door between the warm dock and the cold store. Our cold-chain case study shows a computer working at that interface. Our cold chain monitoring FAQ explains how temperature data is collected along the route. For sealed systems with no airflow at all, conduction cooling moves heat to a cold plate or enclosure wall.
Quick answers on condensation
Condensation on electronics: common questions
What is the dew point?
The temperature at which air becomes saturated. Cool air below it and water vapor turns to liquid. The more moisture in the air, the higher the dew point.
Does a waterproof enclosure stop condensation?
No. IP ratings test against water from outside. Moist air sealed inside can still condense when the enclosure cools, so add a breather vent, heater or desiccant.
How long should cold electronics acclimatise?
Typically a few hours. Keep the equipment sealed in its bag or case until it reaches room temperature. Larger, heavier equipment takes longer.
Does conformal coating prevent condensation?
It prevents most of the damage, not the water. Coating keeps moisture off the tracks and components, but water still forms on uncoated connectors and surfaces.
What does non-condensing humidity mean?
That no liquid water forms. A rating such as 5 to 95% RH non-condensing means the equipment is tested in humid air, but not with droplets forming on it.
We build fanless and wide temperature computers for cold, humid and outdoor sites as standard, and can specify the enclosure, heating and coating with them. Tell us the temperatures, humidity and duty cycle, and we will recommend how to keep the system above the dew point.