Buying a Heat Treatment Kiln: ISPM 15 Guide for UK and US

A heat treatment kiln is an insulated chamber with heaters, fans and core-temperature probes that heats wood packaging until the core of the thickest piece reaches at least 56 °C for 30 continuous minutes, the ISPM 15 heat treatment (HT) schedule. Pallet and crate makers, sawmills and recyclers need one if they want to treat wood themselves and apply the ISPM 15 mark under an authorised national programme, rather than buying pre-treated timber.

What a heat treatment kiln is and how it works

ISPM 15, the international standard for wood packaging material, sets the result and leaves the equipment open: wood must reach a minimum of 56 °C for at least 30 continuous minutes throughout its entire profile, including the core. Dielectric heating (DH) is a separate method requiring 60 °C for one continuous minute through the whole profile, including the surface; see dielectric heating.

A conventional HT kiln combines five elements:

• Chamber. An insulated room or container with tight doors and seals, loaded by forklift.
• Heat source. A burner, boiler (hot water, steam or thermal oil), electric heater banks or waste heat, delivering heat through exchangers or coils.
• Fans and air guidance. Circulation fans and baffles move hot air through the stack; reversible fans even out cold spots.
• Humidity control. Wet and dry bulb sensors and vents or steam spray. Moist air transfers heat better and limits checking; very dry air with wet wood slows core heating.
• Probes, controller and data logger. Thermocouples drilled into the core of the thickest pieces feed a controller that starts the 30-minute count only when every probe is at 56 °C, and a logger that stores the cycle record for audits.

Heat treatment is not the same as kiln drying: a heat-treated pallet can still be wet. See kiln dried vs heat treated and heat treatment of wood packaging.

PHOTO 1Open heat treatment kiln chamber with stacked pallets, circulation fans and core probe cables visibleassets/img/rehber/buying-a-heat-treatment-kiln-1.jpg

Kiln types

More detail on designs is in heat treatment kilns: types and sizing.

How to size a kiln

Kiln capacity is quoted in standard pallet equivalents per charge or in cubic metres of stacked wood. The useful figure is daily throughput:

Daily throughput = pallets per charge × charges per day

Cycle time depends on:

1. Thickness of the largest component. Blocks and stringers set the pace; thick cants need many hours.
2. Moisture content and species. Green and dense wood heats more slowly.
3. Starting temperature. Frozen or cold wood in winter adds heating time.
4. Stacking and airflow. Gaps between stacks and correct orientation shorten cycles.
5. Heater power and humidity control. Under-powered heaters stretch the warm-up phase.
6. Loading, unloading and cooling. Handling time between charges can approach the heating time.

Example (illustrative only): a plant ships 1,500 pallets a day in peak season. A kiln holding 400 pallets with a total turnaround of 4 hours (about 2.5 hours heating, 30 minutes hold, 1 hour unloading and reloading) completes 4 charges in a 16-hour, two-shift day: 400 × 4 = 1,600 pallets. That leaves only about 7 % margin; a buyer would test winter cycle times or consider a larger chamber or a second kiln. Plan loading lanes and buffer storage with pallet factory layout in mind.

Buying checklist

1. Capacity. Size for peak demand plus margin, using cycle times measured on your own pallet types, not catalogue figures.
2. Insulation and doors. Ask for wall and roof panel specifications, seal design and how heat loss is guaranteed.
3. Airflow. Fan count, air velocity, reversibility and baffles; ask for a temperature uniformity test.
4. Probe count and type. Enough thermocouple channels for the number your programme or agency sets at qualification, plus spares.
5. Controller and logger acceptance. Confirm with your UK assessment agency or US inspection agency that the software, printouts and data files are acceptable before ordering.
6. Tamper-resistant records. Data that cannot be edited, time-stamped cycle reports, backups and export to PDF or CSV.
7. Calibration. How probes and loggers are calibrated, by whom, at what cost, and whether a calibration certificate is supplied at commissioning.
8. Energy source and consumption. Fuel use per charge under stated wood moisture, and heat recovery options.
9. Electrical and safety conformity. UK buyers should ask for UKCA or CE conformity documents; boilers and steam systems fall under pressure equipment rules. US buyers should check local electrical and fire codes. Confirm specifics with a local engineer.
10. Installation and foundation. Who supplies the slab, fuel connection, flue, power and permits.
11. Commissioning and training. Test charges with your auditor present, operator training on probe placement and records.
12. After-sales service. Response times, remote diagnostics, local technicians.
13. Spare parts. Availability of probes, fans, burner parts and controller boards.
14. References and warranty. Visit operating customers in the same country and compare warranty terms for chamber, heater and controls.

Requirements in the United Kingdom

Authority and legal basis

In the United Kingdom, the Forestry Commission is the plant health authority for wood and wood packaging, working within the Defra plant health system. In Great Britain the legal basis is the assimilated version of Regulation (EU) 2016/2031: Article 96 states that the ISPM 15 mark may only be applied by a registered operator authorised under Article 98. The earlier Plant Health (Wood Packaging Material Marking) (Forestry) Order 2006 (SI 2006/2695), which gave the marking programme statutory status, is now listed as revoked. Northern Ireland follows separate arrangements; producers there should consult DAERA.

The programme in practice is the UK Wood Packaging Material Marking Programme (UKWPMMP), administered by the Timber Packaging and Pallet Confederation (TIMCON) and set up by the Forestry Commission and the Northern Ireland Forest Service together with the trade.

Who needs authorisation

Any company that manufactures, repairs or remanufactures ISPM 15 wood packaging, or marks packaging built from pre-treated timber, must be a UKWPMMP member and, according to GOV.UK guidance, register with the Forestry Commission as a professional operator to apply ISPM 15 marking.

Step-by-step procedure

1. Download the application pack from UKWPMMP and return the signed Application for Registration with the fee to TIMCON.
2. Nominate a "designated person" with technical knowledge of production, treatment and marking.
3. Choose an approved assessment agency and book the first assessment; the producer (FC) number is issued at this stage.
4. Pass the assessment, which covers wood sources, stock reconciliation, treatment method and capacity, segregation of treated and untreated wood, and the designated person's knowledge of ISPM 15, debarking and pest signs.
5. Receive the certificate, issued by the Forestry Commission via TIMCON and valid for six months.
6. Renew no earlier than one month before expiry, with reassessment.

The application pack quotes registration and renewal administration fees, while assessment fees are negotiated with the agency; check current amounts with TIMCON.

Kiln and record requirements

The Forestry Commission's published heat treatment standard (Plant Health Service Information Note, revised June 2003) set out the following for kiln approval:

• an initial test charge with an absolute minimum of 13 probes, spread through the stack including corners and centre, inserted into the wood core away from nails;
• one probe per run for continuous monitoring once approved, kept in the same validated positions;
• data recorded at least every 30 minutes until the slowest-heating wood has held 56 °C at the core for 30 minutes;
• UKAS-certified data logging equipment, with probes and loggers calibrated every 12 months by a UKAS-accredited body and certificates kept for assessors;
• a wet bulb depression not exceeding 5 °C; dehumidification kilns running at 45–55 °C were considered unlikely to qualify.

The note dates from before the 2009 revision of ISPM 15, so buyers should confirm the current probe, calibration and record retention rules with their assessment agency before specifying a kiln.

The mark and registration number

The UK mark carries the IPPC symbol, the country code GB, a hyphen and the producer code starting with FC (for example GB-FC0001; leading zeros are optional), with the treatment code HT below it or separated by a hyphen. The mark may be rectangular or square. See the ISPM 15 mark.

Inspections and sanctions

Members are reassessed every six months. Forestry Commission plant health inspectors audit the assessment agencies and may enter premises, examine equipment and records, take samples and remove unauthorised marks; marking equipment may be seized and certificates withdrawn for non-compliance.

Requirements in the United States

Authority, legal basis and who needs approval

In the United States, USDA APHIS is the NPPO. Under memorandums of understanding with APHIS, the American Lumber Standard Committee (ALSC) Board of Review runs the Wood Packaging Material programme and accredits independent inspection agencies; ALSC reports 15 accredited agencies serving about 5,300 facilities. Producers enrol with one agency. They either build packaging from ALSC-accredited HT lumber or heat treat finished packaging to 56 °C core for 30 minutes.

Procedure

1. Select an ALSC-accredited agency and sign a service agreement.
2. Set up record keeping and in-facility quality control procedures approved by the agency.
3. Have the agency verify chamber temperature devices and, where required, run a verification study.
4. Start marking only after qualification; inspections follow at least 12 times a year at roughly monthly intervals.

Kiln and record requirements

The ALSC Enforcement Regulations (7 November 2025) require an appropriate number of thermocouples located to measure the temperature actually achieved, annual calibration of monitoring and recording equipment for each chamber, recalibration or replacement when variance exceeds ±5 °F (±2.8 °C), and requalification after major equipment changes. Facilities may monitor by wet and dry bulb, dry bulb only with adjusted times, or direct core probes sealed with non-conductive material. Verification studies are required for dry-heat schedules below 160 °F (71 °C) and wet-bulb schedules below 140 °F (60 °C). Agencies keep inspection records for at least two years. Operation details: operating a heat treatment kiln.

Mark and sanctions

The mark contains the IPPC symbol, US with the producer number, the facility name or number, HT (plus KD if applicable) and the agency's logo or name, applied on at least two opposite sides; tags are not allowed. Agencies may warn, suspend or withdraw a facility; after a suspension or withdrawal, no other agency may serve it for 180 days.

Other countries

Canada runs ISPM 15 certification through the Canadian Food Inspection Agency (CFIA), including the Canadian Heat Treated Wood Products Certification Program. Australia operates the Australian Wood Packaging Certification Scheme (AWPCS), owned by the Department of Agriculture, Fisheries and Forestry. Check each scheme's kiln rules directly.

PHOTO 2Inspector reviewing a kiln data logger printout next to a heat treatment chamberassets/img/rehber/buying-a-heat-treatment-kiln-2.jpg

Costs and running expenses

No official price list exists for kilns, and quotes vary widely. The main capital drivers are chamber size, construction (panel, brick or container), heat source and boiler, controller and logging software, and site works such as foundations, flues and power upgrades. Running costs come from fuel or electricity per charge (rising sharply with wet or frozen wood), fan power, probe replacement, annual calibration, programme and assessment fees, operator time for records, and maintenance of burners and fans. Biomass systems trade higher capital cost for low fuel cost where residues are available; electric and gas units are cheaper to install but more exposed to energy prices.

FAQ

Sources

1. Wood packaging material for import and export — UK Government / Forestry Commission
2. Regulation (EU) 2016/2031, Article 96 (as applies in GB) — legislation.gov.uk
3. UKWPMMP application pack — UK Wood Packaging Material Marking Programme / TIMCON
4. UK heat treatment standards (Plant Health Service Information Note, 2003) — Forestry Commission via IPPC
5. UK implementation of ISPM 15 — IPPC
6. Wood Packing Treatment Programs — USDA APHIS
7. Wood Packaging Material Program — American Lumber Standard Committee
8. WPM Enforcement Regulations (7 November 2025) — American Lumber Standard Committee
9. ISPM 15: Regulation of wood packaging material in international trade — IPPC / FAO