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Writer's pictureMikael Denut

How is the airflow measurement and adjustment of air volumes performed?

Measurement and Balancing of Ventilation Systems


The measurement and balancing of ventilation systems are key processes that ensure the air we breathe indoors is clean and fresh. Many customers are interested in the measurement and adjustment of air volumes. During our work, we often receive questions about what we are doing and why, how our devices work, and what they display. Is this a good or bad thing? While we strive to be helpful, the measurement and adjustment of air volumes are tasks that require professional expertise and cannot be taught on the fly. This article aims to help our customers understand what we do and why. It seeks to clarify the process of measuring and adjusting air volumes and to explain clearly and simply why ventilation air volumes are measured and adjusted, what tools are needed, and how the entire process proceeds.


The technicians at IVAeris Oy measure and adjust the airflow rates of the ventilation system to ensure clean and fresh indoor air.

Why Are Air Volumes Measured and Adjusted?


A ventilation system brings fresh outdoor air indoors and removes dirty air. This is important because ventilation:


  • Removes impurities such as dust, odors, and moisture.

  • Brings in fresh air, which improves the quality of the breathing air.

  • Reduces the risk of mold and other harmful substances.


The air volumes must be balanced because if significantly more air is brought into a dwelling than is removed, positive pressure is created, which pushes moisture accumulated from living into the structures. Moisture accumulated in the structures provides a base for mold growth and can damage the building’s structures and lead to health risks. You can read more about the importance of pressure relationships in our article “What is Negative and Positive Pressure and How Do They Affect Ventilation?



It’s easy to think that when you set the same amount of supply and exhaust air on the ventilation unit’s display, the job is done. Unfortunately, it’s not that simple. Firstly, there are significant differences between different spaces. A smaller amount of air is sufficient for a storage room, whereas the living room or bedroom needs plenty of oxygen because people spend time there. The ventilation system also consists of more than just the ventilation unit and vents. Long duct lines and various duct parts, such as T-joints or bends, cause pressure losses, which means that even if the unit indicates a certain air volume being pushed into the ductwork, the same amount of air does not reach the end of the line. Therefore, even if the unit is set to push the same amount of supply and exhaust air, the actual result is not the same as the set air volume. This is why measuring and adjusting air volumes is crucial for health, living comfort, economic efficiency, and housing safety.


Regulations and Guidelines


In Finland, the air volume produced by ventilation has been thoroughly studied and defined for different spaces and usage conditions. For example, regulations require that a single-occupancy bedroom must supply at least 6 liters of air per second. This is based on the fact that an adult man at rest exchanges about 0.5 liters of air per breath (0.4 liters for an adult woman) breathing 12 times per minute, which results in approximately 6 liters of air ventilation (J Breath Res. 2021 Sep 27). The purpose of ventilation is also to keep indoor air clean and remove moisture and dust generated by human activity. Therefore, it is understandable where the regulatory values come from. In Finland, there is no need to individually study the required air volumes for different situations, as we can rely on government regulations and established standards.


The measurement and balancing of ventilation systems in Finland are based on certain regulations and guidelines that ensure the proper and safe functioning of ventilation and that air volumes are suitable for the spaces and sufficient for the occupants. There is a wealth of information on regulations and guidelines, for example, from the following publications:




Air Exchange Rate


An important performance metric in ventilation is the air exchange rate. The air exchange rate indicates how many times the air in an entire space is replaced per hour. According to Finnish regulations and standards, the air exchange rate in residences must be at least 0.5 times per hour, meaning the air is completely replaced every two hours. For example, in a 100 square meter apartment with a ceiling height of 2 meters, there are approximately 200 cubic meters of air, which must be completely replaced within 2 hours. This translates to an air exchange rate of 100 cubic meters per hour, or about 28 liters per second. Therefore, the air volume measurement report for a residence can easily verify whether the adjusted air volume meets the minimum ventilation requirements. This ensures that the air remains fresh and clean.


At IVaeris Oy, we use the latest guidelines and continuously train our staff to deliver our services at the highest level. For instance, we are one of the few companies that has obtained the IV measurement qualification granted by FISE through the Finnish HVAC Association SuLVI ry (as reported in “IVAeris has obtained air ventilation measurement and adjustment qualifications!”).


Adjustment Tools, Methods and Styles


Various tools and methods are used in adjustment work to achieve optimal ventilation. Airflow rates of ventilation valves are measured with a measuring probe and measuring stick, while a feeler gauge is used to measure the adjustment position of the valve. A pressure difference meter measures the air pressure differences in the valves, and the adjustment guide provides the manufacturer’s instructions for adjusting the valves. A calculator is needed for calculating airflow rates.




Several methods are utilized for measuring the ventilation system. In pressure difference measurement, the pressure difference between the valves is measured. A hood meter measures the airflow directly from the valve, while a Pitot tube measures the airflow velocity. A hot-wire anemometer measures both the temperature and speed of the airflow, and a vane anemometer uses a rotating vane to measure the airflow speed.


Methods of Airflow Adjustment


There are several methods for adjusting airflows, but in our opinion, the only correct style is relative adjustment. Next, we will introduce the most common adjustment methods: Coffee Break Adjustment, Valve-Specific Adjustment, and the only correct style (according to IVAeris Oy), relative adjustment.


Coffee Break Adjustment

Coffee Break Adjustment is a humorous term that refers to situations where airflow adjustment has been neglected or done carelessly. Such an adjustment does not correspond to actual airflows. Unfortunately, we often encounter measurement and adjustment records that have nothing to do with actual airflows. Adjustment cannot be done solely based on the preliminary adjustment values in the ventilation plans or general rules of thumb.


Valve-Specific Adjustment

Valve-Specific Adjustment is a commonly used airflow adjustment method due to its speed. However, speed does not guarantee quality work. The adjustment starts by setting the fans to the desired level, after which the airflow of each valve is adjusted. In valve-specific adjustment, each valve is individually adjusted to the correct ratio. This method is faster than relative adjustment but is not as energy-efficient and often noisier.


In valve-specific adjustment, there is a risk that the pressure of the initially adjusted valves changes as the adjustment progresses, causing their values to no longer match the target values. Therefore, the adjustment must be checked and possibly corrected after the first round. When done carefully, valve-specific adjustment can take almost as long as relative adjustment.


IVAeris Oy often encounters situations where airflow measurement and adjustment have been neglected or poorly executed. If a ventilation measurement professional adjusts the entire system by throttling the valves more and more to achieve the required airflows while simultaneously increasing the machine’s rotation speed, the ventilation unit will be noisy and the system will not be energy-efficient. The correct style is to leave the weakest valve fully open (reference valve) and throttle the other valves accordingly to achieve maximum benefit and a quietly operating, energy-efficient system.


Relative Adjustment

Relative Adjustment is the most energy-efficient and optimal method for adjusting ventilation. The adjustment starts with the valve with the smallest airflow or pressure. The installer adjusts the other valves so that all valves have the same ratio as the reference valve. This method ensures uniform airflow throughout the system.


Adjustment work requires constant back-and-forth between the reference valve and the other valves to account for the effects of the adjustments. For example, if the reference valve has 50% of the target airflow, the flow of the other valves is also adjusted to 50%. Finally, the total airflow is adjusted from the fan. Relative adjustment is laborious but definitely the most energy-efficient solution.



Styles of Airflow Adjustment


Airflow measurement and adjustment should always be performed using the relative method, as it is the only style to ensure an approved and energy-efficient result. Although there are various adjustment styles for different situations, the adjustment does not need to be redone each time if it has been done correctly once.


Inspection Measurement and Fine Adjustment

In inspection measurement and fine adjustment, the ventilation is adjusted so that the power of the ventilation units is correct and the adjustments of the terminal devices can be made so that most of the terminal devices can be adjusted to the correct values in one adjustment round. Some terminal devices must be measured twice to ensure an acceptable result. In this style, there is no need to adjust the machine at different speeds, and the previous measurement record can be utilized. First, an inspection measurement is performed on a smaller area to verify the reliability of the previous measurement record. If the previous measurement record does not use a reference valve (left fully open), it is uncertain whether the adjustment was done correctly. Based on a reliable measurement record, the terminal devices can be adjusted in one round in addition to the inspection measurements.


Thorough Re-Adjustment

In the thorough re-adjustment method, the ventilation system is completely re-adjusted as in new building adjustment work. This includes adjusting the power of all ventilation units, and the terminal devices are visited multiple times during the work, adjusting each valve relative to the reference valve. This method is implemented in new buildings, after more extensive ventilation renovations, or in cases where the ventilation has not been previously adjusted correctly. IVAeris Oy typically performs all adjustments according to this style because we rarely encounter systems where the adjustment has been done correctly.


Inspection Measurement During Cleaning

In the inspection measurement during cleaning, the terminal devices are inspected by comparing them to the results of the previous measurement record. If the ventilation measurement and adjustment were done correctly the last time, the ventilation system can be left at the old adjustment values and verified as correct. If the values are incorrect, either fine adjustment or thorough re-adjustment should be performed.


Airflow Measurement and Adjustment


When measuring and adjusting airflows, the airflow is first checked from the ventilation drawing or measurement record. Then the manufacturer and size of the valve are determined, and only then is the pressure difference (Δpm) measured from the valve with a meter. The airflow (qv) is calculated using the formula qv = k x Δpm, where qv is the airflow (l/s), k is the coefficient, and Δpm is the measured pressure difference (Pa). The valve is adjusted by turning its plate in or out. Depending on the valve manufacturer, these adjustments are usually specified with millimeter precision, so residents should not touch these at all.


When the valve is set to the correct adjustment position, the next valve or diffuser is adjusted. Diffusers in residential areas are adjusted by taping the holes of the diffuser from the inside with adjustment tape or placing magnetic strips on them. This too is very precise work, as often the number of small holes must be counted and covered or opened correctly. When all valves and diffusers are adjusted to the correct position relative to the reference valve (left open), the adjustment is complete. This method is performed separately on the supply and exhaust sides, meaning the reference valve is defined separately for the exhaust and supply air sides before the adjustment.


When the adjustment is complete, an overpressure measurement of the envelope is performed. This ensures that the building is balanced or, as we recommend at IVAeris Oy, slightly underpressurized (read why we recommend slight underpressure in buildings). In overpressure measurement, the pressure difference is measured from several sides of the building, taking weather conditions into account. The meter is placed inside the house, and a hose is attached to the outside. If the house is underpressurized, the meter should show a negative value.



Measurement and Adjustment Report for Airflow Rates


When airflow rates have been adjusted or measured and confirmed to be correct, the person performing the adjustment work must provide a measurement report after the work: the Airflow Measurement Report. This document should clearly indicate which spaces have been measured, the address where the work was performed, who performed the work, and with which device. The measurement results must be presented clearly to allow verification of the measurement and adjustment.


The measurement report should include the exact model and size of each valve and its adjustment position. Additionally, the report must state the K-value provided by the valve manufacturer and the measured pressure difference between the terminal device and the room. Without this information, the adjustment cannot be verified, and the report will not be acceptable.


This example report includes the following information:


  • Spaces where airflow measurements were taken: All spaces where measurements were conducted, such as the kitchen, front room, WC, shower, and back room.

  • Property or building identifier: The location where the measurement was performed.

  • Actual flow rate: The measurement results indicating the actual airflow.

  • Required flow rate according to regulations: The airflow rate required by regulations.

  • Exhaust airflow data: Information on the measurements and adjustments of exhaust airflows.

  • Total actual flow rate: The sum of all measured airflows.

  • Total required flow rate: The sum of all airflow rates required by regulations.


With this information, it can be ensured that the airflow adjustments have been correctly made and that the indoor air remains clean and fresh.



The adjustment report of the ventilation system displays measurement data of airflow rates in different spaces. The report includes the following information: spaces where airflow measurements were taken, property or building identifier, actual flow rate, required flow rate according to regulations, exhaust airflow data, and the total amounts of both actual and required flow rates.

Measurement and balancing of ventilation systems are essential procedures that ensure good indoor air quality and energy efficiency. When the ventilation system functions correctly, it removes impurities and brings fresh air into the indoor spaces. This ensures that the building’s occupants can breathe healthy and clean air.


Ensure high-quality and accurate measurement and adjustment of ventilation. If you suspect that your ventilation is not properly adjusted or if you have ventilation issues and care about healthy indoor air, contact IVAeris Oy today!


WE KNOW, WE CARE & WE GET IT DONE


IVAeris Oy

010 206 3000

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