Heat Treatment (HT) for Wood Pallets: ISPM 15 Guide

Heat treatment (HT) heats pallet wood to a 56C core for at least 30 minutes, killing pests chemical-free and meeting ISPM 15 for exports to 100+ countries.

Reviewed and updated by ICD - Week 43/2026

Heat treatment (HT) is the ISPM 15 method of treating wooden pallets with heat: the whole wood cross-section, including the core, must reach at least 56 °C and hold it continuously for at least 30 minutes in a heat chamber or kiln, after which the pallet is stamped with the IPPC mark carrying the code HT. The method uses no chemicals, but it only kills pests at the time of treatment and gives no protection against re-infestation.

56 °C

Minimum temperature at the coldest point of the wood, including the core

30 continuous minutes

If the temperature drops midway, the batch must be run again or extended

Code HT

Treatment code on the IPPC mark; microwave or radio-wave treatment uses code DH

In international trade, pallets and wooden crates are the familiar route by which weevils, longhorn beetles and nematodes travel from one country to another. Heat treatment is the most widely used way to block that route without leaving chemical residue. This article explains what HT is, the mandatory parameters, how a treatment batch runs, who may apply the mark in Vietnam and the misunderstandings that come up when buying HT pallets.

Diagram of the IPPC mark on a heat-treated pallet: VN is the country code, xxx is the treatment facility code (an illustrative placeholder), HT is the method code.

What Is Heat Treatment (HT)?

Heat treatment is the process of heating wood to a temperature and for a time sufficient to kill insects, eggs, larvae and nematodes living in the wood grain, without chemicals. Under the ISPM 15 standard (International Standard for Phytosanitary Measures No. 15), the wood must reach a minimum of 56 °C (about 132.8 °F) continuously for at least 30 minutes across the whole cross-section, including the core. The 56 °C for 30 minutes mark is not a rough estimate: according to the review of wood heat treatment published by the IPPC, it was chosen from studies in the early 1990s on pine wood nematodes and then accepted as the common standard for both insects and nematodes in wood.

In Vietnam the term “hun trung nhiet” (literally “heat fumigation”) is common, whereas in the English text of ISPM 15 the word fumigation is reserved for treatment by gas such as methyl bromide; treatment by heat is called heat treatment. When preparing documents with overseas partners, use the correct term heat treatment to avoid confusion. After a successful treatment the pallet is stamped with the IPPC mark with code HT to show compliance with ISPM 15, helping the importing country prevent alien species.

Which Heating Technologies Count as Heat Treatment?

Under Annex 1 of ISPM 15, the heat source matters less than the result: steam chambers, kilns, pressure impregnation with heating and dielectric heating are all accepted if they reach the right temperature and time. The difference lies in the treatment code on the mark and where the temperature must be measured.

Technology	Code on the mark	Mandatory parameters	Temperature measurement point
Conventional steam heat chamber or kiln	HT	At least 56 °C for 30 continuous minutes across the whole wood cross-section	Wood core, at the coldest position in the batch
Kiln drying (KD)	HT	Counts as HT only when it is shown to reach 56 °C for 30 minutes at the core	Wood core, or per a schedule that has been tested
Pressure impregnation with heating	HT	The heating part must reach 56 °C for 30 minutes	Wood core
Dielectric heating (microwave, radio waves)	DH	At least 60 °C for 1 continuous minute across the whole cross-section, including the surface	Usually the wood surface, the coolest place

In other words, a workshop with a kiln is not necessarily qualified to apply the HT mark. Drying to lower moisture usually runs to a moisture schedule, without a record showing that the wood core held 56 °C for a full 30 continuous minutes; without that record the pallet is only a dried pallet, not a quarantine-treated pallet.

Sawn timber stacked in bundles with spacers under cover at a timber yard — Sawn timber stacked in bundles with spacers for ventilation: drying or air-seasoning lowers moisture, but only counts as heat treatment when there is a record of the core reaching 56 °C for 30 minutes.

Why Is Heat Treatment (HT) Important?

HT matters because it is one of the two most common ways for wooden pallets to meet ISPM 15 and clear customs, and the only one of the two that leaves no chemical residue on the wood. Untreated wood can shelter harmful insects and micro-organisms. When they cross borders with cargo, they can become alien species causing damage to the forests, agriculture and forestry of the importing country. Heat treatment at the right parameters kills these organisms at the time of treatment.

Close-up of rotten wood grain with many bore holes — Wood damaged by boring organisms: bore holes and rotten grain show that the wood once sheltered insects and borers.

A heat-treated pallet can still be re-infested

In a 2021 reply to businesses, the Ministry of Agriculture and Rural Development (now the Ministry of Agriculture and Environment) stated that heat treatment at 56 °C for 30 minutes only kills insects at the time of treatment and has no protective effect against re-infestation. The time before insects reappear depends on storage conditions, weather, wood species and insect species. So store treated pallets in a separate, covered area away from untreated wood and put them into use soon.

Compliance with the International Standard ISPM 15

ISPM 15 is a mandatory requirement for wood packaging material in the countries that apply the standard. Wood packaging with no mark, or found to hold live organisms, can cause a shipment to be held, the packaging to be re-treated or destroyed, leading to storage costs, late delivery and damage to reputation with customers. Section 4.6 of ISPM 15 lists the measures an importing country may apply in this case:

Hold the shipment at the border while the case is handled.
Separate the non-compliant wood packaging or re-treat it on the spot.
Dispose of the wood packaging safely, or return the shipment.

Container yard and gantry cranes at an export port — Wood packaging is checked for the ISPM 15 mark at the border of the importing country; a missing mark, or live organisms found, can mean the shipment is held.

No Hazardous Chemicals

Compared with methyl bromide fumigation (MB), heat treatment uses no toxic gas, so it needs no airing time after treatment and leaves no residue on the wood. HT is also more flexible on bark and size: ISPM 15 allows debarking before or after heat treatment, whereas for MB it must be done before; MB may not be used on wood whose smallest cross-section dimension is over 20 cm, while HT has no such limit. These points make HT fit the trend of reducing chemical use and ever tighter environmental rules.

How Does the Heat Treatment (HT) Process Work?

An HT batch has five steps: inspection, loading the chamber, heating and holding, cooling, and marking; of these, holding the wood core at 56 °C for a full 30 continuous minutes is the decisive step.

Diagram of the wood core temperature curve in an HT batch. The 30-minute clock only starts when the coldest point of the batch reaches 56°C.

Preparation and inspection: reject badly damaged pallets and check for remaining bark on the wood.
Loading the chamber: pallets are stacked with spacers, leaving gaps so hot air circulates evenly around and through the stack of wood.
Heating and holding: sensors are inserted into the core of a board at the coldest point, and the 30-minute clock only starts when this point reaches 56 °C.
Cooling and inspection: take the pallets out, check that the wood is not cracked or warped and check the batch’s temperature record.
Marking: a pallet that passes is stamped with the IPPC mark carrying the country code, treatment facility code and code HT.

What Conditions Must the Heat Treatment Chamber Meet?

ISPM 15 does not prescribe a specific chamber design but sets requirements for the national plant protection organization to approve a treatment provider; the common aim is to measure at the place where the wood heats slowest and keep the evidence. The treatment chamber must be sealed and well insulated, floor included, with circulation fans strong enough that hot air passes evenly around and through the stack; where needed, extra spacers and baffles are used so hot air flows between the layers of pallets.

Temperature measurement is specified in the most detail of all: the treatment provider must identify the coldest point of each batch and place the sensors there. Sensors and data loggers are calibrated according to the manufacturer’s instructions, at a frequency set by the regulator. Three requirements on how sensors are inserted:

At least 2 sensors

Insert to the centre of a board, at least 30 cm from the end of the board; for pallet blocks, insert into the largest block.

Seal the drill hole

So the sensor measures the wood temperature and does not wrongly read the air temperature in the kiln.

Avoid metal

Do not place sensors near nails or metal parts, because metal conducts heat faster than wood.

If the temperature drops midway, the batch must be run again or extended, with more heat if needed, until a full 30 continuous minutes at 56 °C is reached. The temperature record of each batch and the calibration records are kept for inspection. Besides inserting sensors into the wood, the treatment provider may use a treatment schedule based on kiln air temperature, but that schedule must be built from trial batches with core temperature measured at several positions, taking into account wood species, thickness, moisture and air speed, and must be approved by the regulator.

Who May Apply Heat Treatment and the HT Mark in Vietnam?

Only organisations holding a Practising Certificate for treating objects subject to plant quarantine may heat treat wooden pallets. According to a reply from the Department of Crop Production and Plant Protection (Ministry of Agriculture and Environment) on 17 April 2026, based on the 2013 Law on Plant Protection and Quarantine, this is a conditional business line; the conditions for the certificate follow Decree 66/2016/ND-CP, amended by Decree 33/2026/ND-CP dated 21 January 2026, and the procedure follows Decision 278/QD-BNNMT dated 23 January 2026.

Tall stacks of wooden and plastic pallets in a warehouse — Pallets after treatment should be stored in a covered area, separate from untreated wood, to reduce the risk of re-infestation.

The application goes to the Department of Crop Production and Plant Protection (in person, online or by post); within 10 working days from when the application is found valid, the Department inspects the practising conditions on site and decides whether to issue the certificate. For a company buying pallets, a quick check is to ask the supplier for the treatment provider, that provider’s practising certificate that is still valid, and the temperature record of the corresponding batch. Wooden pallets from ICD Vietnam for export cargo are treated and marked with the IPPC stamp under ISPM 15 through a treatment provider holding a practising certificate.

Benefits of Heat Treated (HT) Wooden Pallets

The biggest benefit of HT pallets is that they can go to markets applying ISPM 15 without carrying chemical residue. Using heat-treated wooden pallets brings a few practical benefits:

Safe for goods and workers because no hazardous chemicals are used.
Convenient for export, because the HT mark is accepted by the countries applying ISPM 15 and is less likely to be questioned by partners.
Environmentally friendly, with no emission of ozone-depleting substances such as methyl bromide.

On the Effect of Lowering Moisture

The HT parameters only specify temperature and time, not moisture after treatment. A 30-minute batch at 56 °C does dry the wood a little but does not replace the drying step, so heat treatment should not be seen as a way of increasing pallet hardness or lifespan. If goods are moisture sensitive, such as food, pharmaceuticals and electronics, agree the pallet moisture separately when ordering and check it with a wood moisture meter on receipt.

HT pallets are not the answer to every problem either. If pallets are kept outdoors for a long time, mixed with untreated wood or reused through many cycles, the risk of re-infestation remains. For repaired or rebuilt pallets, the replacement wood must be treated under ISPM 15, and re-marking follows the separate rules for repaired and remanufactured pallets in section 4.3 of the standard.

Conclusion

An HT pallet is compliant when the wood core holds 56 °C for a full 30 continuous minutes, is treated by a provider with a practising certificate and carries an IPPC mark with code HT; after treatment it must be stored in isolation to avoid re-infestation.

Enough heat

Wood core at 56 °C or above for 30 continuous minutes, with a record.

Right provider

Holds a practising certificate for treating quarantine objects.

Right mark

Clear IPPC mark with country code, facility code and code HT.

With our experience supplying pallets for export cargo, we always advise customers to use properly heat-treated pallets, state the destination market when ordering and keep the treatment documents together with the shipment file, so that every shipment passes the border smoothly.

Frequently Asked Questions

What is heat treatment (HT)?

It is a chemical-free wood treatment process that heats the wood to a core temperature of at least 56 °C continuously for at least 30 minutes to kill insects and pests, under ISPM 15. A pallet that passes is stamped with the IPPC mark with code HT.

Which standard does heat treatment follow?

The international standard ISPM 15 of the International Plant Protection Convention (IPPC) on wood packaging material in international trade. In Vietnam the treatment provider must hold a Practising Certificate for treating objects subject to plant quarantine.

Does heat treatment make pallets more durable?

Not significantly. The HT parameters only specify temperature and time; the wood dries a little but this does not replace the drying step. Pallet durability depends mainly on wood species, board thickness and structure.

Tall stacks of wooden pallets outdoors on grass beside a warehouse — Pallets left outdoors on grass next to the yard for a long time create favourable conditions for insects to return, even if the pallets have been heat treated.

Can heat-treated pallets get weevils or termites again?

They can. Heat treatment only kills insects at the time of treatment and does not protect against re-infestation. Pallets mixed with untreated wood, left outdoors or stored for a long time can be re-infested, so store them in isolation, under cover, and use them soon.

Can a pallet that is only kiln dried be stamped HT?

Only if it can be shown that the wood core reached at least 56 °C continuously for 30 minutes, with a temperature record, and it was done by a provider holding a practising certificate. Drying to lower moisture without this record may not carry the HT mark.

Must the wood be debarked before or after heat treatment?

ISPM 15 allows debarking before or after heat treatment, as long as the finished pallet meets the bark remnant tolerance: bark pieces narrower than 3 cm, or wider than 3 cm but with an area under 50 cm² each. For methyl bromide, debarking before treatment is mandatory.

How do HT and DH differ?

HT is conventional heat treatment in a steam chamber or kiln, with the wood core reaching 56 °C for 30 minutes. DH is dielectric heating by microwave or radio waves, with the whole wood cross-section including the surface reaching 60 °C for 1 minute. The two methods use different codes on the IPPC mark.

Contact ICD Vietnam

If you need wooden pallets for export cargo, heat treated and marked with the IPPC stamp under ISPM 15: ICD Vietnam has a manufacturing workshop, a Hanoi warehouse and a southern workshop, and quotes by size, load rating and quantity (price: contact for a quote).

North: 0983 797 186 / 090 345 9186.
South: 098 6784 186; southern workshop: 551/212 Le Van Khuong Street, Tan Thoi Hiep Ward, District 12.
Email: sales@icdvietnam.com.vn.