Quick answer: For most warehouses, hold 45–55 % RH and keep it steady. Go lower for metal parts (below about 45 %), and use sealed dry cabinets for moisture-sensitive electronics. The humidity you need is set by what you store, while the size of the dehumidifier is set mainly by how much outdoor air leaks in through doors and gaps. Seal first, then size.
Quick answer
- General goods and cardboard: 45–55 % RH.
- Metal parts: 35–45 % RH, and keep surfaces above the dew point.
- Leakage and dock doors usually add more moisture than anything stored inside.
For equipment and models, see our warehouse dehumidifiers.
Humidity targets by stored goods
| Stored goods | Main risk | Typical target | Notes |
|---|---|---|---|
| General logistics goods | Mold, odor, label and packaging damage | 45–55 % RH | Stability matters more than a very low number |
| Corrugated boxes, paper, kraft | Moisture uptake, loss of stacking strength, warping | 45–55 % RH | Board strength falls as it absorbs moisture; avoid wide daily swings |
| Metal parts, tooling, castings | Corrosion, flash rust | 35–45 % RH | The Canadian Conservation Institute gives 35–55 % RH for stable metals and advises better control above 55 % (CCI Note 9/2) |
| Electronics and assemblies | Corrosion, condensation, moisture-sensitive components | 30–50 % RH for the room; dry cabinets for sensitive components | Moisture-sensitive devices follow IPC/JEDEC J-STD-033 dry-storage rules |
| Food powders, sugar, hygroscopic materials | Caking, clumping, microbial growth | Set by the product; often below 40–50 % RH | May need desiccant drying in a sealed zone |
| Wood, furniture, paper archives | Swelling, cracking, mold | 40–55 % RH, held steady | Sudden changes cause more damage than a stable value |
Related: CCI Note 9/2.
These are starting points. Use the product owner's or packaging specification when one exists.
Why a "dry" warehouse still damages stock
Cold surfaces. A slab, an outside wall or a metal roof can be several degrees colder than the air. At those surfaces, RH is much higher than the sensor shows, and condensation forms when the surface falls below the air's dew point. This is why warehouses "sweat" in spring: warm, humid air arrives over a floor still cold from winter. See warehouse floor condensation in spring.
Swings. Packaging and wood absorb and release moisture with each change. A warehouse that swings from 40 % to 75 % RH every day can do more harm than one held at 60 %.
Where the moisture comes from
| Source | Typical size | What reduces it |
|---|---|---|
| Air leakage through walls, roof, gaps | Often the largest, all day | Sealing, closing vents, avoiding negative pressure from exhaust fans |
| Dock doors | Large when open in humid weather | Fast doors, dock seals, vestibules, air curtains, shorter open times |
| Wet goods, pallets, rain | Variable | Drying area, covered loading |
| Floor and slab | Seasonal | Vapor barrier, slab warming, dry air across the floor |
| People, forklifts, cleaning | Usually small | Battery forklifts, dry cleaning methods |
Worked example: how much water leaks in
A 20,000 m³ warehouse held at 25 °C / 50 % RH, in humid weather outside at 30 °C / 70 % RH.
- Outdoor air moisture: about 18.8 g per kg of dry air. Indoor target: about 9.9 g/kg. Difference: 8.9 g/kg.
- At 0.5 air changes per hour of leakage (10,000 m³/h ≈ 12,000 kg/h of air): 12,000 × 0.0089 ≈ 107 kg/h, about 2,600 L/day.
- At 0.2 air changes per hour after sealing: about 1,000 L/day.
Sealing the building cut the dehumidifier needed by more than half before buying anything. Leakage rates vary widely; measure or estimate them for your building and ask your supplier to show the calculation. Our sizing guide explains the method.
Refrigerant or desiccant?
| Warehouse condition | Start with |
|---|---|
| Heated or warm warehouse, above about 15 °C, target 45–60 % RH | Refrigerant dehumidifier |
| Unheated in winter, 0–15 °C | Compare both; a desiccant unit avoids coil icing |
| Cold store or anteroom, or a dew-point target | Desiccant dehumidifier |
| Sealed zone for powders or electronics at low RH | Desiccant, often with a small refrigerant pre-cooler |
Related: desiccant dehumidifier.
Getting dry air to the racks
A dehumidifier dries only the air that reaches it. In a high-bay warehouse:
- Spread several units along the building rather than one in a corner.
- Aim discharge along the aisles and toward cold walls and dock areas.
- Use ducted or ceiling units where floor space is taken by racking; see our ceiling-mounted and ducted dehumidifiers.
- Add destratification fans in tall buildings so air does not layer.
- Leave a gap between stock and outside walls so air can move behind it.
- Place sensors at product level in several zones, not only near the office.
RFQ checklist for a warehouse dehumidifier
- Building size, height, construction and insulation
- What is stored, and the target RH or dew point
- Temperature range across the year
- Number of dock doors, door type and typical open time
- Known leakage paths and exhaust fans
- Rack layout and where units can go (floor, wall, ceiling)
- Power supply and drain points
Send these to us and we will calculate the load and propose the layout and models from our warehouse dehumidifier range.
FAQ
Frequently asked questions
What is the ideal humidity for a warehouse?
45–55 % RH for most stock, held steady. Lower for metal parts; follow the product specification for sensitive goods.
What humidity damages cardboard boxes?
Board absorbs moisture and loses stacking strength as humidity rises, and repeated swings accelerate damage. Keep storage below about 60 % RH and avoid large daily swings.
At what humidity does metal rust in storage?
Corrosion risk rises with RH and sharply when water condenses on the surface. Hold below about 45 % RH for parts and tools, and keep surfaces above the dew point.
How many dehumidifiers does a warehouse need?
It depends on leakage, door openings and the target, not on floor area alone. Calculate the moisture load, then spread enough units to reach every zone.
Should I ventilate or dehumidify a warehouse?
Ventilate when outdoor air is drier than indoor air. In humid weather, ventilation brings moisture in; seal the building and dehumidify.
Sources
- Canadian Conservation Institute, CCI Note 9/2: Storage of metals.
- IPC/JEDEC J-STD-033, Handling, packing, shipping and use of moisture/reflow-sensitive surface-mount devices.
- ASHRAE Handbook—Fundamentals, Psychrometrics.
