The Studor Airflow Calculator

Drainage Design Calculations
for Designers, Architects and Engineers

The Studor Airflow Calculator is a step-by-step formula based on the European standard EN12056-2. It assists with the calculation of airflow and wastewater flow per second when considering the design of a building’s drainage system. It is an essential formula when considering high rise and multi-storey drainage systems because it gives you an understanding of how your system is likely to perform.

By simply entering the system type which is preferable to your drainage requirement, along with frequency factors and appliances quantities, this useful tool will give you a calculation based on EN12056-2:2000 – Gravity Drainage System inside buildings. This standard is useful in helping you understand the performance of your system whatever the building height. However, it is even more critical when it comes to drainage system design for buildings over 10 floors, especially in Europe, the Middle East and South East Asia, as it is firmly based on flow rate, i.e. litres per second.

What does the Airflow Calculator do?

A calculation table is used to work out the airflow rate requirement on branch and on stack pipes. Together with Air Admittance Valves (AAVs), the calculation is used to determine the diameter requirement of pipe sizes depending on their calculated loading capacity. The calculator encompasses variables such as continuous flow rate, discharge units, water flow rate and focuses of the usage volume for a given drainage system.

The Airflow Calculator tool was develMichael Changoped as an Excel spreadsheet in 2008 by Michael Chang from Studor’s Technical and Product Development department. It was later made available to the drainage design engineers who also face the same day-to-day calculation challenges when designing a building’s drainage system, before being launched as a web-based tool in 2013. The most recent development has been its launch in May 2016 as an iOS App – download it from the Apple Store here. An Android version will be available later in 2016.

When do we use the Airflow Calculator?

We use the spreadsheet formula specifically when designing any high rise or low rise building and their associated drainage system design.

What are the benefits?

As building drainage system designs are becoming more complex, the Airflow Calculator was created to simplify and reduce work load, as a number of calculations are the same and just repeat with a different number of fixtures and factors. It simplifies the calculation and makes the whole process easy to understand for designers, architect and engineers while using the results as reference points.

How to use the Airflow Calculator

Please click here to read the simple step instructions to use the Airflow Calculator.

Need more assistance? Then please speak to a member of our technical team

For further assistance or information regarding the Studor Airflow Calculator or any other drainage matters, please feel free to get in touch with a member of our technical team at

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How to Use the Airflow Calculator

InstructionsAirflow Calculator

The following set of instructions outline how to use the Studor web-based and Airflow Calculator Apps. The input fields are highlighted in pink for the web-based version and are white in the App.

  1. Select the system tab: either System I or II
    1. System I (50%): For single discharge stack system with partly filled branch discharge pipes. Designed with a filling degree of 0.5 (50%) with a single stack.
    2. System II (70%): For single discharge stack system with partly filled branch discharge pipes. Designed with a filling degree of 0.7 (70%) with a single stack.
  1. Select frequency factor of the drainage system
    1. 5 – intermittent use, e.g. in dwelling, guesthouse, office
    2. 7 – frequent use, e.g. in hospital, school, restaurant, hotel
    3. 0 – congested use, e.g. in toilets and/or showers open to public
    4. 2 – special use, e.g. laboratory

Note: For high rise buildings we tend to always use the 0.7 factor as an added safety factor and to cover mixed usage of the building. 

  1. Enter number of fixtures on a typical branch
    1. Enter the total number of each type of appliance, leaving as 0 (zero) if there are none.
    2. To calculate the number of Discharge Units (DU) on the App press “Calculate” or on the web-based Calculator press Enter or Tab.
    3. On the App the branch airflow requirement is the same as Qtot.
    4. On the web-based Calculator enter the continuous flow rate (Qc) and pumped water flow rate (Qp) if necessary (this facility is not available on the App). The branch airflow requirement will be updated accordingly.

Note: Qtot = total water flow rate requirement for the branch, and should be less than the hydraulic capacity (Qmax) detailed in Table 7 of EN12056-2 (see below). This is the minimum branch pipe size for the given total water flow rate.

  1. Enter stack levels
    1. Enter the number of floors of typical branches connected to the stack. The stack airflow requirement will be updated accordingly.

Note: Qww = total water flow rate requirement for the stack, and should be less than the hydraulic capacity (Qmax) detailed in Table 12 of EN12056-2 (see below). This is the minimum stack pipe size for the given total water flow rate.

  1. Email results
    1. To email the calculation results to yourself, which includes the total number of recommended Studor AAVs, click “Email” (App) or “Email results” (web-based version).

Additional Information

The Studor Airflow Calculator is based on European Standard EN 23056-2 – Gravity drainage systems inside buildings.

Sanitary appliances are connected to small bore branch discharge pipes. The small bore branch discharge pipes are designed with a filling degree of 0.7 (70%) and are connected to a single stack.

Control of pressure in the discharge stack is achieved by used of separate ventilating stacks and/or secondary branch ventilating pipes in connection with stack vent. Alternatively, Air Admittance Valves (AAVs) may be used.

Control of pressure in the discharge branch is achieved by ventilation of the discharge branch. Alternatively, AAVs may be used.

Waste water flowrate

The total waste water flowrate is the expected flowrate of waste water in a part or in the whole drainage system where only domestic sanitary appliances are connected to the system. This is calculated as the frequency factor (K) x the square root of the sum of the discharge units.Airflow Calculator Frequency FactorsDischarge Units (DUs) of a variety of sanitary appliances are given values for the purpose of calculation, and are not related to discharge rates of sanitary appliances quoted in the standard.

Total flowrate

Total flowrate is the design flowrate in a part of in the whole of the drainage system where sanitary appliances, appliances with continuous flow and/or waste pumps are connected to the system.

Continuous flows and pump discharge rates shall be added to the waste water flowrate without any reduction.

The total flowrate is calculated by adding together the waste water flowrate, the continuous flowrate and the pumped water flowrate.

Calculation rules

The pipe capacity (see below) shall be at least the larger of:

a) the calculated waste water flowrate or total flowrate; or
b) the flowrate of the appliance with the largest discharge unit.

Airflow Calculator EN12056-2 Table 7
Airflow Calculator EN12056-2 Table 12

Need more assistance? Then please speak to a member of our technical team

For further assistance or information regarding the Studor Airflow Calculator or any other drainage matters, please feel free to get in touch with a member of our technical team at

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The Drop Dead Foundation – saving millions of litres of water!

Over a number of years, Steve White (Studor Technical Director) halogo-WPC-13s regularly attended the World Plumbing Council (WPC)’s triennial World Plumbing Conference. In November 2013 the 10th WPC conference was held in New Delhi, India, featuring environment, health and hygiene as the three main topics covered over three technical sessions – focussing “attention on plumbing as an integral part of the construction business, directly affecting the health of a nation”.

Over 550 delegates from across the world were present, including representatives from Australia, Canada, China, Germany, India, New Zealand, Poland, Singapore, Switzerland, UAE, UK (including Scotland) and the USA.

Of particular interest to Steve was the second Technical Session:

He particularly enjoyed listening to the presentation by Mr Aabid Surti from the Drop Dead Foundation (DDF) about the importance of saving water, and having the opportunity to meet with him personally. What particularly struck him was that Aabid had started out as just an ordinary person (and not as an industry professional or academic) who wanted to make a difference to save one of the world’s finite resources in a very down-to-earth, cost-effective and practical way – and this is exactly what he has been doing since he launched the DDF in 2007.
Aabid, who was born on 5 May 1935, established the DDF in 2007 after a leaking tap at a friend’s house bothered him so much and made him realise the amount of water that could be saved if such problems could be fixed. Ever since, he has been a dedicated hands-on key member of the DDF team, repairing minor plumbing problems (such as leaking taps) for free, and saving millions of litres of water from going down the drain.


Aabid has many “feathers to his bow” – not only is he an environmental activist, but he is an award-winning author, a screenwriter and playwright, an accomplished artist (also having attained a Diploma in Arts in 1960), and long-standing cartoonist – he was the illustrator of the first Indian comic book super hero “Bahadur”.

As the world market leader in our industry, we feel that it is important to be aware of the wider issues which affect our industry, particularly with regard to the world’s resources. With this in mind, this year in recognition of WPD 2016 we supported an initiative of the DDF to create awareness of their work in local community centres across India with the message “Save Water. Save India!”.

On 22 March, World Water Day, DDF announced the launch of their “One Drop Cinema” Competition. Open to resident Indians, it “is a one-minute-film competition to encourage people to create a viral video around the theme of water conservation”. The competition will be judged by actress and social activist Juhi Chawla, writer and director Amole Gupte (Stanley Ka Dabba) and writer and director Subhash Kapoor (Jolly LLB).

We look forward to seeing the results of the competition!

For more information on DDF and Aabid Surti: There are several press links on the DDF website, but a Google search on “Aabid Surti” and “Drop  Dead Foundation” also results in numerous articles about him/the foundation. Aabid was recently interviewed by the BBC as part of their Unsung Indians series, which profiles people who are working to improve the lives of others. Following Aabid’s award early this month of the Lifetime Achievement Award at Bangalore Comic Con 2015, a dedicated website for comic enthusiasts has also published an interview with him, providing further insight into this multi-talented individual.

To keep up-to-date with the work of DDF, please visit their website or “Like” their Facebook page.

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World Plumbing Day 2016

march 11, every year… everywhere

Plumbing – Vital to Global Health
Because Every Day is World Plumbing Day

Today is World Plumbing Day (WPD), which was established in 2010 by the World Plumbing Council (WPC) “to provide anyone or any organisation involved in the global plumbing industry with an opportunity to promote the important role played by the industry.” This annual day of recognition is held on March 11, every year… everywhere!

There are four key elements with which plumbing is associated – water, health, energy and environment. Here are some facts and practical suggestions from the WPC on how you personally can make a positive impact:

WPD brochure_Page_1

This year, in recognition of WPD 2016, Studor has made a donDrop Dead Foundationation to the Drop Dead Foundation to support their valuable work in India of repairing minor plumbing problems, such as leaking taps, for free.

The foundation was established in 2007 by the writer and artist Aabid Surti. A leaking tap at a friend’s house had bothered him so much, and made him realise the amount of water that could be saved if such problems could be fixed. Aabid remains very hands-on and is a key member of the Drop Dead team which hits the road every Sunday, fixing plumbing leaks in Mumbai.

The Drop Dead team is featured below (from left to right): The Founder and Chairman: Aabid Surti, Co-ordinator: Tejal Shah, Plumber: Riyaz Ahmed

DDF Staff

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How to Avoid a Roof Penetration

Reduce Thermal Heat Loss with the Studor Maxi-Vent


The Maxi-Vent fits neatly into the roof space

With modern improved building insulation methods and the importance of reducing thermal heat loss, not compromising the roof’s integrity with penetrations (such as vent pipes) is of great benefit – this is where the Maxi-Vent, together with the associated reduced material and labour savings, provides an environmentally friendly option for the building versus traditional drainage ventilation systems.

Saving Time and Money

The Maxi-Vent is very easy to fit and it will decrease the amount of work and piping – you no longer need to penetrate the roof of a property. It is favoured in residential homes, flats and commercial buildings of any height, and its benefits lead to both cost and time savings.

Protecting Your Living Environment

This advanced AAV protects the trap seals in the drainage system by allowing the intake of air, so a soil pipe can maintain the right level of pressure within the drainage system. By instead installing the Studor Maxi-Vent, the vent pipes terminate in the roof space or lower down the waste system, therefore completely eliminating excessive thermal heat loss and a roof penetration. In addition, it also means that any bad smells will be kept well away from a building’s Air Handling Units (AHUs).

Below is a short video which introduces the Studor Maxi-Vent. More information is available on the Studor Maxi-Vent product page.


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Studor Test Tower in the Press

We’re delighted that the Studor Test Tower has received coverage in the industry press, recognising the importance of this installation in that it offers industry professionals the opportunity to see the evidence that the Studor System works in real life.

You can read the latest articles in the following publications – HPMMagModern Building Services and Society of Public Health Engineers.

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Learning about Building Design in the Big Apple

A Guest Blog from Steve White

Between 26 and 30 October, 2015, I was invited to attend the Council on Tall Buildings and Urban Habitat conference at the Grand Hyatt, New York. This was the first time I’d attended the event, and as a manufacturer in specialist drainage ventilation, I hoped the event would provide an insight into the activities around the world for high-rise buildings, both now and in the future.


The event was attended not only by building services engineers, but also by developers, architects and leading consultants from 45 countries, representing 140 cities across the globe.

A total of 125 papers were presented in total, but my particular interest was in the papers on the Kingdom Tower in Jeddah and the Developments in East Asia. Hearing the views of the architects was interesting in learning how their designs are originated – it is definitely not just to do with making the buildings unique and pretty!


I came away from the conference with a much greater understanding of what goes into the design of tall buildings and towers. It also reinforced to me that these buildings need the Studor System to make them work. No matter how tall, expensive and iconic these buildings are, if they smell they smell, and we, at Studor, have the solutions to prevent bad drainage odours from spoiling the experience of the inhabitants.

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Drusillas Animal Park Returns to Studor for Sewer Gas Solution

Drusillas LogoBackground

Having already solved major sewer gas problems by installing several Maxi-Filtra vents in the past, Drusillas Park, a popular small animal zoo in East Sussex, contacted Studor to obtain Studor vents to prevent problems occurring in an area of new development within the park.


A new project was in development to introduce camels, for the first time, into Drusillas’ roxy-and-lofty-the-camels-at-drusillas-park-1-206llama paddock. However, underneath the paddock was a 45,500 litre sewage balancing chamber which vented into the area where Drusillas wished to build the camel shelter.

Studor Solution

This was not the first time that Drusillas has encountered a problem with sewer drain venting, as they’d experienced similar issues when constructing their ‘Hello Kitty Secret Garden’ and ‘Explorers Café’. In both instances, installing a Maxi-Filtra vent from Studor instantly solved, what could have been a major problem. Therefore, they had no hesitation in requesting another three Maxi-Filtra vents for their new camel shelter.

The Studor Maxi-Filtra is a sturdy and practical vent designed specifically for outdoor applications to eliminate bad odours.


No specialist installation is required for the Maxi-Filtra; it is commonly installed with just a push-fit connector and the cap simply lifts off to enable easy access for filter cartridge replacement. The robust design means the Maxi-Filtra can be used vertically or horizontally and can be installed in hard-to-reach places.

In the case of Drusillas, it has been used to eliminate the bad odours from existing external drainage vent stacks. The Maxi-Filtra can also be used on a number of external applications, including the ventilation pipe of septic tanks, water tanks and silos.


Having being installed in three separate applications across Drusillas Park, the Studor Maxi-Filtra has proved completely successful in eliminating sewer gas emissions and the consequent unpleasant odours.

You can read the full case study here.


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Communicating and Educating

One of the really pleasurable aspects of my position as Technical Sales Director for Studor is the opportunity I have to travel to many different countries.  Also to share and communicate the knowledge I have developed about drainage systems.  There is nothing to compare to the feeling of sharing knowledge with those who WANT to learn…


Although local practices and cultures are very different, the technical challenges of drainage designs in buildings remain very similar and this is true all over the world.

As a sales person for over 20 years I have naturally been involved with prospecting, budgets, negotiations, orders and deliveries.  However, since I started my collaboration with Studor I have also had to become a “teacher”.  I must say that, despite the challenge, this has been a fantastic and rewarding role.

The ability to successfully transfer the knowledge of the world experts at Studor has been an outstanding experience, enriching myself with the pleasure of establishing fantastic personal relationships.  There is nothing better than to witness the emotion on peoples’ faces when a concept is understood!  You really feel a sense of accomplishment.

Finally I can also express my natural extrovert, enjoying the natural communication flow while speaking different languages and using skills I developed as a student when I was a tour guide in Tuscany.

Colombia, Chile, Portugal, Italy, Spain, Israel, The Netherlands, Iran, Sweden, Thailand, Panama, UAE, Qatar, Uruguay and Morocco are just some of the recent locations of my world education tour.

Whilst I try to visit as many countries as possible, please do not forget that many of the resources I use are included in the DRC (Distributor Resource Centre).  If I can assist or if you would like me to visit to help train your sales team and technical staff, please just contact me.

Best regards


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PRoBE – Pathogen Research in the Built Environment

PRoBE is a new research initiative to provide the knowledge to address the growing issues of pathogen spread in building systems.

PRoBE was established at Heriot-Watt University with the aim of characterising and defining the aerosolisation, transmission, and infection risk posed by building systems, particularly the building drainage system.

PRoBE Identity

PRoBE is a cross-disciplinary research group of engineers, mathematical modellers and microbiologists at Heriot-Watt University.  The acronym stands for Pathogen Research in the Built Environment (PRoBE).  The PRoBE logo and more information can be found at the research group website (

It is intended that this cross-disciplinary group will look at a range of different issues relating to infection spread in buildings. Having been established just over a year ago, the group has already had success in highlighting the complex issues in this area and brings a fresh approach to the discipline.

The Group is led by Dr. Michael Gormley and supported by Dr. Tom Aspray who is a microbiologist, and Dr. David Kelly who has worked on building drainage systems for over 10 years.

PRoBE Research

Bioaerosol Transmission

Bioaerosols can pose a significant risk to the spread of infection and disease within buildings. Research activities focus on the characterisation of bioaerosol generation and transmission, coupled closely with the development and application of advanced numerical models for the prediction of bioaerosol transport.

A significant area of research focuses on the transport of bioaerosols within the sanitary plumbing and sewerage system and their cross-transmission into the building. Laboratory tests, using Pseudomonas putida KT2440 as the pathogenic agent within a toilet flush, found that the generated bioaerosols could be spread from one floor of a building to another via the building drainage system. If a defect within the system exists such as, for example, the loss of the seal within a water trap, then the bioaerosols could enter a room on an upper floor and contaminate every surface within that room. Such a cross-transmission route depends on the following confirmed conditions:

  1. The sanitary plumbing and sewerage system is a reservoir of pathogenic organisms.
  2. Bioaerosols are generated during appliance flush.
  3. Airflows within the sanitary plumbing and sewerage system move both in the upward and downward directions and circulate between floors.
  4. Bioaerosols can be transported on the airflows that exist within the sanitary plumbing and sewerage system.
  5. A defect, such as an empty U-bend, allows air to move from the system into the building.

Viral Transmission in Tall Buildings

As a common feature of most global cities, tall buildings offer a number of advantages, whether it be to provide offices or homes when urban space is not available or to make an iconic statement on the world stage. However, these “cities in the sky” can also facilitate the rapid spread of infection from one person to another due to the high density of people in a single building.  Using advanced numerical modelling techniques, researchers at PRoBE were able to confirm the World Health Organisation conjecture that a high cluster of cases of SARS, reported at the Amoy Gardens residences in Hong Kong in 2003, was caused by the vertical transmission of the virus between apartments via both the sanitary plumbing system and the service risers. The 321 confirmed cases of SARS and 42 fatalities suffered by the residents highlight the risk of infection spread within buildings, especially the significance of a vertical transmission route which is particularly unique to tall buildings.

By modelling air flow movement and air pressure wave propagation within the sanitary plumbing system, the PRoBE research was able to demonstrate the likely circumstances within the building that resulted in the rapid spread of the virus. The index patient (the first resident to become infected with the virus) lived on the 16th floor of the 36 storey building. Infected faecal particles were discharged into the building drainage system during the diarrhoeal phase of the infection. The flushing of the WC caused the generation of airborne bioaerosols within the system’s vertical stack. A number of dry floor drains, together with some appliances with no fitted water trap seals, provided a route for the ingress of virus-laden bioaerosols from the building drainage system and into the bathroom, driven by the transient pressures prevailing within the system, natural buoyancy, and the negative pressure created by the bathroom extract fan. After passing through the extract fan, the bioaerosols were then exhausted into the external service riser which acted as a channel to spread the virus to upper and lower apartments via open windows.  This mechanism of viral spread was attributed to the infection of residents in some 11 apartments below the index patient and 27 apartments above the index patient – firmly highlighting the significant risk of vertical transmission of infection in tall buildings.

Infection Spread in Hospitals

With up to 9% of all patients in the UK contracting a Healthcare Acquired Infection and an associated annual cost to tax payers estimated at £1 billion, the control and reduction of the spread of infection in hospitals is a top priority for the NHS in the UK. Researchers at PRoBE have identified the building drainage system as a potentially significant, yet often forgotten, source of infection spread within hospital buildings.

The building drainage system is one of only a few engineered systems that interconnect all parts of a building, and it is the only one that acts a collection network for human waste. In a hospital building, this waste has a high potential for pathogenic contamination, making the building drainage system a potentially rich reservoir for pathogenic microorganisms. Failures within the system, such as empty water trap seals at appliances or wastewater backup due to blockages, can contribute to the spread of pathogens from the building drainage system into the hospital building – considerably adding to the risk of infection spread.

Research carried out by PRoBE in hospital buildings using polymerase chain reaction (PCR) tests on waste water samples confirmed that the sanitary plumbing and sewerage system is contaminated by pathogens released directly to the system by infected patients. In one example, the building drainage system tested positive  for Norovirus GII over a number of weeks during an outbreak within the hospital building.

Furthermore, measurement of the conditions within the hospital sanitary plumbing and sewerage system showed average temperatures of just over 24°C and an average humidity of almost 97%. The warm and humid conditions that exist within the system not only aides pathogen survival, it also facilitates the airborne transmission of aerosolised pathogens around the system, and potentially into the hospital building, through air movement and buoyancy effects.

Laboratory Investigations

At the heart of the work carried out by the PRoBE group is an adherence to excellence in data collection and a rigorous approach to both engineering modelling and microbiological analysis. Molecular techniques such as PCR are used to generate mathematical equations suitable for inclusion in a 1-D method of characteristics model, AIRNET, which is currently being updated to include an algorithm for the simulation of microbial transport on building drainage airstreams.

The work of the PRoBE group is gaining momentum and has contributed to providing solutions to difficult infection spread problems so far. We are hopeful and confident that the group can go on to add to the knowledge base we have started with the aim of providing improved public health for all buildings in the future.

Dr. Michael Gormley, November 2015


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