A reefer is an insulated container with an integral refrigeration unit built into the front wall, used for fruit, vegetables, seafood, meat, dairy, pharmaceuticals and some chemicals. In the Stowage.id catalogue a 20-foot reefer container (22R1) offers about 28.4 m³ of internal volume and a 40-foot high cube reefer (45R1) about 67.7 m³. Size matters, but what really decides the outcome is cargo temperature at stuffing, airflow and clean paperwork.

20RF and 40RF dimensions

The insulated walls and the machinery at the front take up space, so a reefer is noticeably smaller inside than a dry box. A standard 20ft container, for comparison, is 5,898 mm long inside.

Specification (typical values) 20RF (22R1) 40RF high cube (45R1)
Inside dimensions (L × W × H) 5,444 × 2,294 × 2,276 mm 11,583 × 2,294 × 2,550 mm
Door opening (W × H) 2,290 × 2,264 mm 2,290 × 2,569 mm
Floor area 12.49 m² 26.57 m²
Internal volume 28.4 m³ 67.7 m³
Tare 3,080 kg 4,800 kg
Max gross mass 30,480 kg 34,000 kg
Max payload 27,400 kg 29,200 kg

Treat these as typical figures and always check the CSC plate and door markings of the unit you receive, because tare and payload vary by manufacturer. A 20RF takes about 9 pallets of 1200×1000 or 10 EUR pallets on the floor; a 40RF about 20 of 1200×1000 or 23 EUR pallets (theoretical single tier).

How air moves inside a reefer

The unit blows cold air in at floor level through a T-section floor (T-floor). Air travels along the channels between the floor rails, rises up through the cargo and returns to the machine through the space above the stow. Three rules follow from that:

  • Keep the T-floor working. Cover the floor evenly with pallets; large open gaps let air short-circuit back to the unit instead of passing through the cargo. Close remaining gaps.
  • Never load above the red line. The red load line on the side walls marks the maximum height. The space above is the return path for the air.
  • Frozen and chilled cargo behave differently. Frozen goods are usually block-stowed tightly because they only need to be held at temperature. Fresh produce is still respiring, so it needs ventilated packaging and a stacking pattern that leaves vertical air channels.

Set point, ventilation and humidity

The set point is the temperature requested on the booking and programmed into the unit. Modern units can typically be set around −30 °C to +30 °C, depending on the unit; some products call for specialised equipment. The right temperature is defined by the product and the buyer, not the carrier.

Fresh-air exchange is set in m³ per hour to remove gases such as ethylene and CO₂ given off by fruit and vegetables; for frozen cargo the vents are normally closed. Humidity can be controlled on units with a dehumidification function. All three values belong on the booking and the shipping instruction, because a single wrong figure can ruin the whole load.

Use the Reefer Calculator to check capacity and the basic requirements of your load before you send the booking request.

Pre-cooling, PTI and stuffing

A reefer maintains temperature; it does not pull large amounts of heat out of the cargo. Bring the goods down to carrying temperature in cold storage first. A typical sequence:

  1. Pre-cool the cargo in a refrigerated warehouse and measure the core (pulp) temperature.
  2. Accept a unit with a valid PTI. The pre-trip inspection tests the machinery, sensors and alarms. Check cleanliness, odour, drain holes and door gaskets yourself.
  3. Verify the unit settings: set point, ventilation and humidity as per booking.
  4. Stuff quickly, ideally from a refrigerated dock so the cold chain is never broken. In common practice the unit is switched off while the doors are open so it does not draw in warm, humid air; follow the carrier's instructions.
  5. Close, seal and restart. Record the container seal number, the cargo temperature at stuffing and the time the unit was restarted.

Pre-cooling an empty container without a cold dock can backfire in tropical air: condensation forms the moment the doors open. Agree with the carrier whether the unit should be pre-cooled at all.

Power, gensets and the voyage

A reefer needs power continuously. At terminals and on board it plugs into reefer sockets; on the road the trailer carries a genset (clip-on or underslung). Make sure that:

  • Time without power, for example between genset and terminal plug, is kept as short as possible.
  • The terminal has reefer slots available on the arrival date; plugs are limited in peak season.
  • Reefer monitoring and power charges at the terminal are usually billed separately; amounts vary, so check the operator's or carrier's official tariff.
  • The unit's data logger records temperatures throughout the trip; request a download if you claim.

Worked example: frozen fish in a 40RF

An Indonesian exporter ships frozen fish on 1200×1000 pallets to Japan in a 40RF:

  • 20 pallets, each carrying 1,100 kg of cartons on a 25 kg wooden pallet.
  • Cargo height 2,000 mm plus pallet 150 mm = 2,150 mm per pallet.

Step by step:

  1. Cargo weight: 20 × (1,100 + 25) = 22,500 kg, comfortably below the 29,200 kg payload.
  2. Height: 2,150 mm against an inside height of 2,550 mm leaves 400 mm. Confirm the top of the stow stays below the red line of that particular unit.
  3. Volume used: 20 × 1.2 × 1.0 × 2.15 = 51.6 m³, about 76% of 67.76 m³. In a reefer, filling less than the full cube is normal because the air needs space above the cargo.
  4. Estimated VGM: 22,500 + 4,800 kg tare = 27,300 kg (plus any dunnage), below the 34,000 kg max gross mass. Check road limits for the trailer leg in Indonesia as well.

This is a simulation. The official figure must come from weighing or an approved method for the VGM; see the VGM SOLAS guide and prepare the declaration with the VGM Form.

Documents and special requirements

Beyond the usual export set (commercial invoice, packing list, bill of lading), reefer cargo often needs:

  • A booking that states set point, ventilation and humidity unambiguously.
  • A health certificate or phytosanitary certificate from the Indonesian Quarantine Agency (Barantin) for animal, fish or plant products, as the destination requires.
  • A record of stuffing temperature and seal number to support claims and insurance.

The export and import documents guide has the full list.

Common mistakes

  • Loading cargo that is not yet cold, hoping the unit will bring it down during the voyage.
  • Stacking above the red line or blocking the T-floor with loose cartons and plastic sheets.
  • Mixing up units (°C vs °F) or losing the minus sign on the booking.
  • Vents open for frozen cargo, or closed for fruit that needs air exchange.
  • Forgetting the heavier reefer tare, which pushes VGM and road weights over the limit.
  • No power plan at the depot or terminal when the box has to wait.

Plan your reefer load

Start by checking the unit in Container Sizes, then lay out pallets and the height limit in the 3D Load Planner to see whether the stow stays below the red line. A planner layout is a simulation; it does not replace carrier instructions, official weighing or operator approval.