International shipping presents a lot of challenges, but moisture is one of the biggest obstacles in global shipping. Moisture doesn’t just affect the quality of goods, it can also lead to hundreds of thousands of dollars in damage.
Fortunately, you can prevent moisture damage by dehumidifying your shipping containers. That might sound like a lot of work, but it’s simpler than you might expect. Check out this guide to learn everything you need to know about how to dehumidify shipping containers.
Sealed shipping containers trap humid air, which results in condensation that creates an environment where mold and corrosion thrive. Detecting built-up moisture early on helps you minimize damage to the shipping container and your precious cargo.
When moisture builds up in a shipping container, it creates an environment where mold and mildew thrive. Microscopic mold spores feed on cellulose, creating a foul odor and potential health hazards. In some cases, customs may reject your shipment.
Built-up moisture also speeds up the corrosion process, causing floor supports, door hinges and corner casings to rust. This rust weakens load-bearing points and shortens the life of your shipping container.
As the cargo inside your shipping container repeatedly dries out and gets wet again, that moisture causes wooden pallets to warp and cardboard boxes to sag. In some cases, significant damage to cardboard boxes can cause the contents to spill out and contaminate other cargo.
Moisture trapped beneath tarps or between stacked items can lead to a wide range of cargo damage, including corrosion of electronics, staining of paper products and mold on textiles.
When the warm, moist air makes contact with the cold metal walls of shipping containers, droplets form on the inside surface of the container. These droplets build up and eventually fall onto the cargo below, causing significant damage.
Even a small amount of condensation can damage sensitive goods like electronics, precision instruments and pharmaceuticals.
Varying climates also have a significant impact on moisture levels inside shipping containers. In coastal or tropical climates, dew points are often above 70° F and relative humidity (RH) typically stays above 80%. In arid inland regions, RH can be as low as 20% during the day with higher nighttime RH levels creating a condensation risk.
When you’re looking at how to dehumidify shipping containers, make sure you adapt your strategy for different seasons and shipping routes.
Desiccant products are designed to remove moisture from the air through a process called adsorption. Using roughly one pound of desiccant per 150-200 cubic feet helps protect cargo from moisture damage. Desiccants should be positioned evenly on walls, corners and above cargo racks.
Desiccants have color-change indicators that let you know when it’s time to replace or regenerate the pack.
You can also use electric dehumidifiers to control moisture levels inside shipping containers. A 20-30 pint per day dehumidifier is ideal for 20-foot containers, but a 50+ pint per day dehumidifier may be necessary in tropical climates.
Integrated climate control units combine dehumidifiers, heating and air filtration for complete climate control. These climate control units are ideal for high-value or sensitive shipments, but they require 120V or 220V power.
Roof-mounted solar fans can also be used to draw air through louvered vents, maintaining consistent airflow without grid power. It’s important to calculate panel wattage and give yourself a buffer for cloudy days.
Static vents work with natural convection, while powered vents boost air exchange rates up to 300 CFM. Placing vents at the tops and bottoms of the sidewalls creates a cross flow that keeps your cargo dry.
Insulating your shipping container can also help prevent moisture damage. Spray foam has a high R-value and can be used to seal gaps, and closed-cell spray foam doubles as a vapor barrier.
There are also interior coatings and liners with built-in vapor barriers that prevent heat transfer and reduce cold spots on walls to minimize condensation.
Calculating container volume is the first step to figuring out how to dehumidify shipping containers. The formula for container volume is simple:
Once you know the volume of your shipping container in cubic feet, you can choose an appropriately sized dehumidifier based on how many pints or liters it removes each day. Make sure you factor in moisture releasing from products like wet textiles and fresh lumber.
To figure out how much it costs to run a dehumidifier, look at the power draw in watts and daily estimated kWh usage. Multiply the daily kWh usage by local electricity rates to figure out how much it costs to run your dehumidifier each day.
Once you know the daily operating cost, you can compare it to the cost of desiccants or solar fan installation.
Maintenance is key to maximizing the life of fans and dehumidifiers. Vents and fans should be cleaned monthly, filters should be checked quarterly, and desiccant indicators should be checked twice a month.
Small dehumidifiers typically last 2-5 years while solar fans last 5-10 years. Sticking to a maintenance schedule can help you extend the life of these components.
Before you install a dehumidifier in your shipping container, pressure-wash the floors and walls to remove rust, repair dents and sidewall gaps and make sure the door gasket creates a strong seal to keep unwanted humidity out.
Dehumidifiers should be mounted on raised platforms or brackets to protect against minor flooding. Vents or fans should be positioned at opposite ends of the shipping container to encourage the cross flow of air. Leave 6-12 inches around intakes and outlets to avoid blocking them.
Vents should be sized at 0.5-1% of floor area per vent bank. Intake vents should be placed in the lower part of your shipping container with exhaust vents placed higher to prevent natural convection. Protective louvres help keep out pests and rain.
Place a calibrated digital hygrometer near the center and ends of the container to identify humidity gradients. If you’re using wireless data loggers, set alert thresholds at 60-65% RH.
Once a month, you should follow a routine maintenance checklist:
Small household dehumidifiers can only remove 10-15 pints a day, so they’re not suitable for global shipping. Match the capacity of your dehumidifier to your container volume and cargo type for the best results.
Clogged or broken vents can cause moisture to be trapped inside your shipping container, negating the effects of your dehumidifier. Inspect vents regularly and check to make sure gaskets and vent screens are intact.
Grid outages or extended cloudy periods can interrupt dehumidifier and solar fan usage, causing rapid humidity spikes. Battery backups, dual dehumidifiers and crossover systems can help you quickly react in the event of an outage.
No, household dehumidifiers are only designed to remove 10-15 pints of moisture per day. For a 20-foot shipping container, you need a dehumidifier with a capacity of 20-30 pints per day.
Desiccant packs should be inspected monthly and replaced when the color-changing indicator changes colors.
A relative humidity level of 45-55% is ideal for shipping containers, but it depends on the cargo you’re shipping and the surrounding climate.
Electric and solar units are more effective because they force more airflow, but passive vents are an excellent way to reduce moisture without power.
There’s no single solution to protecting shipping containers from moisture. Combining ventilation, insulation, dehumidifiers and desiccants is the most effective way to protect your cargo.
Constant monitoring, routine maintenance and periodic inspections can help you make sure your cargo is safe no matter the destination.
Sandra Malouf is the President of Eurolog Packing Group and has spent her career focused on Industrial Packaging. With a proven track record of helping businesses avoid supply chain disruptions, Sandra’s visionary leadership elevates the industry. She’s committed to developing sustainable practices and continues to shape the future of industrial packaging by listening to the customer and offering unique solutions applicable to various industries across the world. The company’s main focus is temperature stabilization and moisture damage prevention in exports affected by extreme variations in global temperatures.
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