Container glossary
What is the load line in a reefer container?
The load line is the red line marked near the top of the inside walls of a refrigerated container, showing the maximum height to which cargo may be stacked. The space above it has to stay open, because that is where air travels back to the cooling unit.
Reefer volume below the load line
| Container | Internal L × W × H | Volume |
|---|---|---|
| 20 ft reefer | 5.44 × 2.29 × 2.28 m | 28.3 m³ |
| 40 ft high cube reefer | 11.58 × 2.29 × 2.55 m | 67.3 m³ |
Data: Hapag-Lloyd Container Specifications · Maersk Container Specifications
The air path the red line protects
A reefer cools from the floor up. The machine at the front end blows cold air into the T-shaped floor gratings, the air runs the length of the box under the cargo, rises through and around it, and returns along the ceiling to the machine, where it is measured and cooled again. The load line marks the bottom of that return channel.
Stack above the line and the return path narrows or closes. Air then takes the shortest way back, the far end of the box is no longer swept, and the machine regulates on air that does not tell it the temperature of the cargo. This is also why the usable space of a reefer is less than its internal dimensions suggest — the table above gives the volume for each size, and the reefer container page the rest of the specification.
Finding the line and loading under it
The line is painted or taped on the side walls inside, a short way below the ceiling. It typically leaves about 2.2 m of usable height in a 20 ft reefer and about 2.5 m in a 40 ft high cube reefer. Measure your tallest pallet against that, wrapping and top boards included, before the truck arrives and not at the dock.
Staying under the line is half of the rule. Cover the floor as evenly as you can, so that air is forced up through the cargo instead of escaping through a bare patch; keep the floor channels clear; and leave a little space at the door end. How many pallets each reefer takes is in the table in pallets in a 40 ft container.
One carton too high
The usual mistake is a top layer that crosses the line by a few centimetres — an extra tier of cartons added to use the space. Nothing looks wrong when the doors close. During the voyage the cargo at the top and at the far end warms, and the damage is found at destination as soft fruit or partly thawed product in exactly those positions. A temperature claim follows, and one of the first things a surveyor photographs is the stow against the red line.
A related error is expecting the machine to make up for it. A reefer holds a temperature; it is not built to pull warm cargo down, and it cannot cool what its air does not reach. Cargo goes in already at carriage temperature, and under the line.
Frequently asked questions
How high can you load a reefer container?
Up to the red load line and no higher — typically about 2.2 m (7′3″) in a 20 ft reefer and about 2.5 m (8′2″) in a 40 ft high cube reefer. The exact height is marked inside the unit you are given.
Why is there a red line inside a reefer?
The red line shows the maximum cargo height, so that the gap above it stays open for air returning to the cooling unit. Cargo stacked over it blocks the circulation and lets part of the load warm up.
Is a reefer load line the same as a ship’s load line?
No, they only share a name. A ship’s load line, the Plimsoll mark, is painted on the hull and limits how deep the vessel may sit in the water; the reefer load line is inside a container and limits how high cargo may be stacked.