Effects of Temperature and Humidity- Why do we need to monitor?

with 15 Comments
Temperature and Humidity displayed in Fluke 971
Temperature and Humidity displayed in Fluke 971

Temperature and humidity are the most monitored environmental factors based on the facilities I have visited. You can see it almost everywhere.

Have you ever experienced being exposed to a high temperature and humidity environment? I believe all have experienced it, but not just aware of the effects of temperature and humidity in our daily activities or some of our activities.

In this post, I will present the following:
1. Importance of monitoring these environmental conditions, specifically temperature and humidity in a calibration laboratory.

2. The negative effects of having it very high or very low as applicable to some processes or activities.

3. The related clause and requirements as per ISO 17025:2017

4. The requirements to observe when choosing a monitoring instrument for temperature and humidity.

I will also introduce the instruments used to measure both temperature and humidity in a calibration process.

In our Daily Activities……..

Have you ever experience

During summer when temperature and humidity are high, have you ever experienced in your skin that when you perspire, it stays longer making you uncomfortable? And during winter when the air is very dry it makes our skin and throat also dry.

These feelings (discomfort and irritation) we encounter are the effects of temperature and humidity in our bodies. In our home, wooden types of furniture that get very dry tend to crack or expand. Because of this, we should be familiar with the importance of temperature and humidity monitoring to prevent and control these things that happen in our daily processes.

Ideally, Relative Humidity (RH) should be within the range of 30% to 50% and the temperature is within 20 to 25 deg Celsius. Above this will cause fungus or molds to grow, and below this will cause dryness and discomfort.

Some common examples of why we need to monitor and control temperature and humidity  are:

  1. fruits-and-vegetables
    Fruits and Vegetables in a temperature-controlled room

    To prevent the formation of molds and fungus that can cause diseases,

  2. Maintaining a certain product fresh in a storage room where fruits and vegetables are stored, 
  3. To monitor the environment for fermentation like in beer or winemaking or for incubation of eggs, 
  4. To ensure the maintenance of good quality in some special personal collections like  paintings, guitars or clothing,
  5. To give a healthy environment, for example, maintaining good air quality to avoid dryness on skin and eyes that causes discomfort and breathing-related illnesses like asthma.


Temperature and Humidity in Calibration Laboratory

As required in ISO 17025:2017, the requirements under clause 6.3, the laboratory environmental conditions should be monitored and controlled. Two of these environmental conditions are the temperature and humidity.

The monitoring of environmental conditions is a requirement under ISO 17025:2017. Below are the clauses:

  1. Clause 6.3 Facilities and environmental conditions, with sub-clauses:
    • 6.3.1 The facilities and environmental conditions shall be suitable for the laboratory activities and shall not adversely affect the validity of results.
    • 6.3.2 The requirements for facilities and environmental conditions necessary for the performance of the laboratory activities shall be documented.
    • 6.3.3 The laboratory shall monitor, control and record environmental conditions in accordance with relevant specifications, methods or procedures or where they influence the validity of the results.

Suitability of environmental conditions inside the laboratory especially temperature and humidity should be determined first and strictly implemented before performing the calibration or other laboratory activities. This will ensure that any errors encountered are not caused by the changes in temperature and humidity or environmental conditions and will not contribute an error to the calibration or test performed.

The requirements for temperature and humidity that are suited for the proper performance of equipment and for the achievement of correct calibration results should be documented. Every parameter has its own temperature and humidity requirements that we need to document and follow.

These requirements can be seen or based from:

  1. Manufacturer’s manual
  2. Standard guides and manuals like ASTM or NIST publications
  3. Regulatory requirements – from one of the assigned government agencies of a country
  4. Accreditation bodies’ requirements or policies

The requirements of environmental conditions, like temperature and humidity, that are controlled means that there is a specified range or conditions of acceptability that we need to maintain.

It should be monitored, which means that there is a specified interval for checking if it is meeting the acceptable range/conditions or not, and it should be recorded for the purpose of reviewing the results and as evidence of monitoring and documentation.

We are monitoring and controlling the temperature and humidity to eliminate or reduce its efffect on the validity of the measurement results generated from calibration or testing activity conducted.

Furthermore, monitoring and control are not just during the calibration process but also during the storage and handling of equipment which also includes the calibration status of measuring instruments (example, the thermo-hygrometer).

This is how important it is to consider these two parameters because failing to follow and consider them can cause a lot of problems where discontinue of calibration work is imposed if this requirement of humidity and temperature is not met.

And technically speaking, this is not just applicable to instruments in a laboratory but also in equipment or machines used in manufacturing that is why it is also controlled inside the facilities of every manufacturing company.

Temperature And Humidity in Calibration Reports

Moreover, temperature and humidity are not only recorded in a monitoring sheet, but it is also required to be recorded in the calibration or test report during the actual execution of the laboratory activity like during calibration. Below is the related clause where it is required to be recorded on the calibration report.

  1. Clause 7.8.4 Specific requirements for calibration certificates
    • The calibration certificate shall include b) the conditions (e.g. environmental) under which the calibrations were made that have an influence on the measurement results;

Calibration certificates, test reports, or simply measurement reports should reflect the environmental conditions at the time of performing the measurement.

This is to ensure that we perform the calibration on acceptable environmental conditions where it has no effect on the validity of the results and enables us to repeat the process when necessary which is a part of maintaining traceability of measurement results.


What are the Effects of Temperature and Humidity in our Instruments and Calibration Process

A Sensitive Dial Gauge
Effects of temperature in dimensional calibration can be experienced by a sensitive instrument – like a high-resolution Dial Gauge

There are guides and recommended practices for the use of temperature and humidity in a laboratory. You may find it through the NIST handbook, ISO guides, or NCSL on their websites. 

Requirements for a dimensional lab for temperature and relative humidity (RH) is 20 +/-1 with an RH of 30% to 40% 

Electrical or electronics is within 23 +/-3 Deg C  temperature and a humidity of 35% to 55%.

Please take note that the provided requirements is not fixated on every lab, it is still based on the equipment specifications so the best thing to do is to check first all instrument specs before performing the calibration.

It is a best practice to record all the necessary environmental requirements specifically temperature and humidity of a specific instrument for calibration for easy reference.

Does Temperature Affect Humidity?

Temperature can affect the humidity, they are inversely proportional, meaning, as temperature increases, humidity decreases, and vise versa.  So in order to control humidity, we need also to control the temperature.

Reasons Why we Monitor and Control Temperature and Humidity Inside a Calibration Laboratory

While monitoring temperature and humidity is a requirement of the Standards, below are some reasons:

  1. In pressure calibration, density changes with temperature.
  2. Dimensional calibration where the use of gauge blocks and other dimensional instruments are affected by thermal change usually a temperature higher than 20 Deg C. If you are calibrating or measuring highly accurate instruments, this will be a problem.
  3. With a humidity >60%, metals like gauge blocks will rust quickly.
  4. In an electrical area, when metal rust or corrosion occurs, this will create a leakage path for voltage and current which causes a malfunction or inaccurate reading.
  5. In a load cell, a change in ambient temperature will cause a change in sensitivity.
  6. If below 20%, where the air is very dry,  it will be prone to static electricity which can damage electronic equipment.
  7. Most of the manufactured instruments have a requirement on their environmental condition in order to function at their full accuracy. You may check it on its specifications.
  8. During the storage and transfer phase, after receiving and after performing calibration, the storage area’s temperature and humidity should also be monitored and controlled. Condensation or moisture build-up will occur when an instrument is transferred from a cold to a warm environment.

Because of these reasons or effects of uncontrolled parameters, temperature, and humidity are included as one important factor in the area of quality control. This is also to ensure that any detected errors in the readings of calibrated instruments are not the cause of temperature and humidity variations.


The Requirements for Instruments Used to Measure and Monitor Temperature and Humidity

There are no specific requirements or specifications of a thermometer or hygrometer that the standard requires to be used during monitoring,  but it is advisable to use a continuous recorder of temperature and humidity that is available and directly seen or observed inside the laboratory.

If you are searching for an instrument to be used for monitoring temperature and humidity, below are some criteria/requirements to meet (as per my experience during audits):

    1. The temperature and humidity monitoring instrument should be calibrated before and during use;
    2. The temperature and humidity output display must be easily accessed  during the performance of calibration – to be recorded in the datasheet in real time;
    3. Previous data can be extracted for review or if requested;
    4. Recorded data can be stored for a defined period.

In monitoring temperature and humidity, we can use a separate thermometer and a humidity meter or hygrometer. But why waste our resources if we can have both in one instrument. There is now the Thermo-hygrometer, a hygrometer thermometer meter in one.  Today’s advancement,  a chart recorder is also included depending on the manufacturer. The advantage of monitoring and recording is already in place..

For the procedure in calibrating a Thermo-hygrometer and other details, please visit my other post in this link.

An Example of Thermohygrometer – Extech Humidity-Temperature Chart Recorder Review

Extech RH520A Humidity and Temperature Chart Recorder with RS-232 Computer Interface

Temperature and humidity (relative humidity) monitoring involves data recording and review. It is where we base our analysis on their effect whether it is acceptable or not. Since there is analysis and review involved, we need to have a clear picture of what is to be analyzed.

This is where this instrument is a big help, it does not only display the reading but it also records and displays data in a chart from previous hours or days. Monitoring will be easy because you can directly observe the highest or lowest reading based on its chart.

In the lab that I worked for, Extech RH520A Humidity and Temperature Chart Recorder (Model RH520) is the Thermo-hygrometer that we are using. Its capability meets our expectations where it is a perfect tool for the job (as per my experience).

What I Like in this product (Pros/Features)

  • Its probe (where sensors are located) can be mounted to different positions depending on your needs. It has a stretchable cable ( 1 meter) to be positioned easily. You can place the probe inside a confined space if you need to without including the whole unit like inside a refrigerator.
  • The unit can be used with a battery ( AA) or power supply and therefore can be portable and carried to a different remote location. It is also designed to be mounted on a wall or just placed on a tabletop.
  • It has a memory where data is stored and can be extracted on a defined schedule.
  • Programming or setup is easy to follow based on its user manual, user-friendly.
  • Temperature and humidity are digitally displayed plus a chart to view the past and current state. Also to view and analyze if temperature differences or fluctuations have happened. The display is large enough for you to see it easily at a distance.
  • Data can be extracted to Excel format in a computer ( Laptop) to further review and analyze ( need to install the software provided).
  • It can also display the date and time when monitoring can be analyzed together with temperature and humidity.
  • With a low battery indicator
  • The alarm can be set for proper timing and notifications when needed.

What I Dislike in this product (Cons)

  • I am not sure if this includes all the models but sometimes when I connect it to my laptop, it has difficulty communicating. It will search first for the exact port before communication or connection takes place.
  • The storage memory is not that very big where data should be downloaded on a defined schedule (say 1 month, but I guess this is already good enough if the download schedule is shorter), then reset again to clear and have a fresh start to save and record a new data. This is applicable if you need the past data for storage and future review.
  • Needs to reset time and date if the power is accidentally turned off (battery can be a backup power if installed) or battery is changed (not a big deal).

Who it is for

This is primarily useful in almost every temperature and humidity monitoring, especially in room environment monitoring. If you want to make your monitoring more detailed with some automated features, this one is for you.


Dimensions 5.0×7.7×0.9″ (127x196x23mm)
weight 357g / 12.6oz
temperature Range -28°C to 60°C(-20 to 140°F )
Temperature Accuracy ±1°C / ±1.8°F
Humidity Range 10 to 95% 
Humidity Accuracy ±3.0% typical
Internal Memory Storage 49 152 complete reading sets
Sample Interval selectable recording rate: 0.1 to 199.9 minutes
Graph scaling User selectable in 10 , 5 and 10% increment

For Extech RH520A Calibration Procedure, please visit this link

Note: I get commissions for purchases made through links in this post.


Temperature and humidity are the 2 most monitored environmental conditions in a laboratory where neglecting to monitor, control, and maintain these will result to a non-conformances during an audit.

In this article, I have presented the below topics:
1. Importance of monitoring these environmental conditions, specifically temperature and humidity,
2. The negative effects of having them very high or very low as applicable to some processes or activities.
3. The related clauses and requirements as per ISO 17025:2017.

4. The requirements that we need to observe when choosing the instrument used to monitor temperature and humidity

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15 Responses

  1. In preparation for this upcoming winter season, we plan to have transmission calibration for our HVAC systems and chambers. This article provides us with the importance of monitoring temperature and humidity so as to have a healthy environment. Such informative article!

    • Hi Sariah,
      Thank you for taking time reading my article. I appreciate your positive comments, glad you liked it.

      Best Regards,

  2. John
    | Reply

    Great job.I found it useful


    • You are welcome Sir, Appreciate your comment.

      Best regards,

  3. Ong Zheng Da
    | Reply

    Hi Sir,

    The manual states that “Influences that can adversely affect the validity of results can include, but are not limited to, microbial contamination, dust, electromagnetic disturbances, radiation, humidity, electrical supply, temperature, sound and vibration.”. Is it necessary to address all influences or we can state humidity and temperature as the main concern?

    Thanks and best regards

    • Hi Ong,
      It is not necessary to address all influences if that influence has no effect in your lab activity.

      Temperature and Humidity are the two main environmental conditions that we need to monitor and control because it has an effect on almost all of our lab results in terms of equipment maintenance and measurement output if this is not controlled especially in dimensional calibration.

      But if you observe other influences that have an effect, then you need to address them. For example, there is a strong vibration during mass calibration wherein a stable reading is difficult to achieve resulting to additional error, then you need to include it.
      Some accreditation bodies have requirements or guidelines on every calibration field or parameter so it is also advisable to check them out if you are applying.

      I hope this helps. Thanks again for reading my post.

      Best Regards,

  4. senthilkumaR
    | Reply

    Great Explanation,If possible please post ISO 17025 latest standard free version.

    • Thanks for reading my post. You can check it out here a summarize version and the list of needed documents as per ISO 17025:2017.

      Thanks and regards,

  5. Rohan Labde
    | Reply

    Very informative article. Thank you for sharing this.

    • Hi Rohan,
      You are welcome. Thanks for reading my posts.

      Best regards,

  6. Vinod
    | Reply

    Dear Mr. Edvin,
    Thanks for your valuable post. It will be helpful for all of us if you can guide us for standard format of operating procedure which are required in Calibration lab. My query in that whether we have to prepare the SOP as per reference equipment wise or as per device under calibration wise. For example, while calibrating multimeter, we require the SOP as per multimeter used for calibration or as per standard used for calibration as in this case multi product calibrator. If prepare according to reference or master equipment then multiple parameters will be there.
    Your prompt response is most awaited.

    • Dear Mr. Vinod,

      You are welcome. Thank you for continuously reading my posts.

      The SOP are for both the Master and DUC.

      As per the calibration lab perception/view, we will publish our CMC or calibration capability, and basing from there, we can determine the DUC (Device Under Calibration) that we can calibrate. There are guidelines or method that we can follow to be included to our SOP like the Euramet guide or simply the manufacturer’s procedure.

      Procedures are not the same, some procedures are written for a specific instrument and some are for general instruments but belonging to the same group like multimeters but it is based on the capability of the master standard.

      The important thing is that, before we perform the calibration or create the SOP, we should be familiar with the Master Standard specifications or capability. This also where method validation is performed.

      When you are already familiar with your Master Standard, then you can prepare the SOP as per the DUC requirements. You can even create a general procedure that applies to that specific Master Standard. For example, a multimeter, voltmeter, or an ammeter can use the same SOP using the multiproduct calibrator considering only what is applicable.
      Remember that whatever limitations that we see, or range that we cannot perform calibration for the DUC, this must be communicated first to the user for approval.

      I will try to consider in my future post if I can create a simple guidelines or format for an SOP.

      I hope this helps,

  7. Michael, Greece
    | Reply

    Thanks Edwin for this valuable post. Dealing mainly with uncertainties, sometimes we neglect these, perhaps important, sources of error.

    • Hi Michael,
      I agree with you, and, in order to appreciate more its effects, you need to be familiar with the calculation of measurement uncertainty.

      Thanks for reading.

      Best regards,

  8. KAPIL
    | Reply

    Dear Edwin,
    i have GOETZE 812 series pressure relief valve i want to set it in 5.5 bar what i can do to do it manaully

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