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The Data Center Humidity Problem
IT equipment tolerates a wide range of conditions, but not both extremes. Too much moisture risks condensation and corrosion; too little raises the risk of electrostatic discharge. Economizers and dry winter air make the low end the more common problem.
Too much moisture: condensation and corrosion
When air in a data hall reaches its dew point on a cold surface, water condenses on equipment. High humidity combined with airborne pollutants also speeds corrosion of circuit boards and connectors.
ASHRAE caps its recommended range at a 15°C (59°F) dew point and 70% RH, or 50% RH where gaseous contamination is high.
Too little moisture: ESD risk
Dry air lets static charge build up on people and equipment. When it discharges, it can disrupt or damage components, especially during hands-on work such as installs, swaps and repairs.
ASHRAE’s recommended low end is a -9°C (15.8°F) dew point. Running near the allowable minimum depends on strict ESD controls such as grounding, wrist straps and conductive flooring.
Non-Wetting Humidification for Data Centers
Smart Fog turns water into dry fog, droplets small enough to evaporate in the air before they reach racks or floors. Sensors and controllers hold your dew point or RH setpoint, and the evaporation takes heat out of the air.
The range to hold
ASHRAE’s Thermal Guidelines (5th edition, 2021) recommend server inlet air at 18 to 27°C (64.4 to 80.6°F), with moisture between a -9°C and 15°C dew point (15.8 to 59°F) and no more than 70% RH.
Many operators control to dew point rather than RH, because dew point stays the same as air warms on its way through the racks. In the UK and Europe, the same guidance applies to humidification for data centres.
No wetting, no condensation
The fog is fully absorbed into the air, so there is no water on floors, under raised floors or on equipment.
The controls hold moisture below your upper dew point limit, keeping cold surfaces clear of condensation.
Humidity that cools the hall
Steam humidifiers add heat to air you are paying to cool. Evaporating dry fog absorbs heat instead: at 25 lb of water an hour, that is roughly 26,000 BTU an hour of cooling effect.
That makes adiabatic humidification a natural partner for economizers, which bring in cold, dry outside air in winter.
Fits the way your site is built
Smart Fog systems mount on walls, hang in open halls or install in air handling units.
Optional Modbus and BACnet integration sends humidity readings and alerts to your building management system.
Why Humidity Matters in Data Centers and Server Rooms
Holding moisture inside ASHRAE’s recommended range protects hardware and keeps operations predictable:
- Lower ESD risk during maintenance and hardware changes
- Less corrosion risk from condensation and high humidity
- Stable conditions inside the recommended envelope, all year
- More hours of free cooling, with moisture restored by adiabatic humidification
Benefits of Smart Fog Humidifiers for Server Rooms
What a non-wetting system adds over conventional humidification:
- No water on floors, under raised floors or on equipment
- Humidity held within 1 to 2% of setpoint
- About 0.4 kW per unit at full output, against roughly 8 kW for electric steam
- A cooling effect instead of added heat
- No boilers, drain pans or steam lines to maintain
Data Center Humidification Solutions From Smart Fog
Systems scale by adding units, from a single server room to a full data hall.
Each unit adds up to 25 lb of water an hour. Smart Fog sizes the system to your outside air, airflow and target dew point. Options include:
- ES100 direct space humidifier: a wall-mounted humidifier for server rooms and smaller halls
- TS100 in-duct humidifier: installs in air handling units or supply ducts
- ES100M portable humidifier: on wheels, for commissioning and temporary needs
- MS100 custom grid: for large halls, up to 10,000 sq ft per system
Sizing Humidification for a Data Hall
Humidification load depends mostly on how much outside air you bring in and how dry it is. For example, 5,000 cfm of 20°F outside air needs about 120 lb of water an hour to reach 45% RH at 70°F, or five units. The humidifier sizing calculator gives a first estimate, and a Smart Fog engineer confirms the design.
Why Data Centers Choose Smart Fog
Smart Fog has specialized in non-wetting humidification for more than 40 years, and every system is made in the USA. Its dry fog technology is patented.
For data centers, that means humidity without water near equipment, without the heat of steam, and with controls that connect to your building systems.
FAQs
What humidity should a data center maintain?
ASHRAE’s Thermal Guidelines (5th edition) recommend inlet air with a dew point between -9°C and 15°C (15.8 to 59°F) and no more than 70% RH, or 50% where gaseous contamination is high, at 18 to 27°C (64.4 to 80.6°F).
Why does ASHRAE use dew point instead of RH?
RH changes as air heats and cools, so the same air reads differently in the cold aisle and the hot aisle. Dew point measures the actual moisture in the air and stays constant as it moves through the racks.
How low can data center humidity go?
ASHRAE allows down to a -12°C (10.4°F) dew point and 8% RH for class A1 to A4 equipment, but only with strict ESD controls in place. Sites with frequent hands-on work often keep a higher minimum.
Will a humidifier cause condensation on servers?
Not a Smart Fog system. Dry fog evaporates before it reaches surfaces, and the controls hold moisture below your upper dew point limit. Upkeep is mainly filter changes and periodic inspection.
Do humidifiers work with free cooling and economizers?
Yes, and adiabatic humidifiers suit them best. Economizers bring in cold, dry outside air in winter; dry fog restores the moisture and absorbs heat as it evaporates, rather than adding heat like steam. Integration with your BMS is available over Modbus or BACnet.