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ROUTINE CALIBRATION OF COMPOST THERMOMETERS MAINTAINS EQUIPMENT

ACCURACY

The purpose of windrow composting of HPAI related poultry 

carcass mortality is inactivation of avian influenza virus. Compost 

pile temperature measurements are a critical indicator of 

effectiveness of the compost process for virus inactivation. 

Temperature monitoring is performed by a compost subject 

matter expert (SME), regulatory monitoring staff, contractors, or 

farm personnel. Accurately monitoring and recording daily 

temperatures is vital to demonstrating that the composting process meets time and 

temperature requirements designated by USDA-APHIS. These time and temperature 

requirements must be met as part of the process to release quarantine on the infected 

premises.

THE THERMOMETER SHOULD BE CALIBRATED BEFORE FIRST USE AND, AT A 

MINIMUM, WEEKLY

Calibration should also be performed if any of the following occurs:

♦ It is dropped on a hard surface or subjected to severe shock 

♦ It is subjected to forces causing excessive pressure or bending of the stem 

♦ It is subjected to prolonged vibration 

♦ It is exposed to extreme temperatures outside the range of the dial 

♦ The calibration screw on the back of the dial is turned accidentally 

FY2016 HPAI Response

Calibration of Analog Thermometers

March 22, 2016

The calibration process described below is appropriate for 

most commercially available dial-type compost 

thermometers. Compost thermometers commonly in use for 

HPAI response are 36” or 48” length bimetal dial industrial 

compost thermometers (such as the 5/16” stem heavy duty, 

or 3/8” stem with 1⁄4” fast response tip super duty) 

manufactured by Reotemp Instruments. 

Common bimetal dial compost thermometers

Note: If the stem of the thermometer is bent or the dial is un-sealed 

or broken, the thermometer should be discarded and another 

procured. It is recommended that, where possible, thermometers 

be purchased with and fitted with a “probe handle” or “probe guard” 

for safer handling and protection of the stem and dial. 

Probe handle Probe guard
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MATERIALS NEEDED TO PERFORM CALIBRATION:

♦ Sturdy pail or bucket

♦ Cold water

♦ Ice (crushed or small cubed)

♦ Flathead screwdriver

♦ Compost temperature log or calibration form

♦ Pen or pencil

CALIBRATION INSTRUCTIONS:

1. Assemble a water bath of known temperature, typically an ice bath 32°F (0°C). Place 

enough ice in the bucket to have at least 6” depth, adding just enough water to fill spaces 

between the ice pieces. Let sit for one to several minutes.

2. Agitate (stir) the bath just before and occasionally during calibration.

3. Immerse thermometer tip at least 4” into bath, as the sensitive portion of the thermometer

is the last 2-3” of the stem. Be sure tip does not touch sides or bottom of bucket.

4. Leave thermometer in the bath for at least one minute. 

5. If the dial does not read 32°F, using the flathead screwdriver, turn the small (1/4”) hex 

screw head on the back of the dial case of the thermometer until the pointer is at 32°F. 

Turn the screw counter-clockwise to increase temperature or clockwise to decrease 

temperature.

6. When adjustment is complete, re-check the thermometer in ice water. Repeat adjustment if 

necessary.

7. Each time a thermometer is calibrated it is to be documented that calibration was 

completed. Information can be recorded on the compost temperature log or a separate 

calibration form. Include an equipment identifier, date, reference temperature (32°F), and 

name of the individual performing the calibration.

Probe tip Ice bath 320 F Calibration temperature

Hex screw 

adjustment

Hex screw