HRS is the market leader in Air Testing and Air Tightness Consultancy, with over 30 years experience of providing practical and technical advice, ensuring that our clients have cost-effective solutions and their risks are minimised. Two way communication ensuring that your project hands over on time and in budget is HRS’s number one priority.

Something HRS cannot emphasise enough is to contact HRS early, even if you think it’s too soon to be thinking about Air Testing it is never too soon, a call to HRS will cost you nothing but could save you lots – HRS are here to help.

If you are unsure of the Air Tightness services you require please call 0800 030 4391 or email and one of HRS Air Tightness Consultants would be happy to guide you through the process.

Air Testing and Air Tightness Consultancy

What services you require will depend on many factors but as a rule of thumb, if you’ve got a low air tightness specification of <5m3/(h.m2) or you have multiple contractual and design interfaces, you will need consultancy advice. The best way to be safe and ensure you pass your air test first time is to contact HRS. It will cost you nothing to call and one of HRS’s Air Testing experts will be happy to assess your project and advise you on what services you require minimising your risk.

A HRS consultant with many years of air tightness and building experience will review your drawings and other information and identify potential risk areas, advising you on details, materials and any possible improvements. This service has saved some of HRS’s clients thousands.

If you are not sure if you need this service, give HRS a call, we are here to help – a call costs you nothing and can save you lots

One of HRS’s highly experienced Air Testing experts will come to your site and have a meeting with your project team or an individual (whichever is most appropriate for you). The on-site design review will determine how air testing has been incorporated into the design, how responsibilities across details and interfaces are being allocated and where improvements and cost savings could be made.

If you are not sure if you need this service, give HRS a call, we are here to help – a call costs you nothing and can save you lots

One of HRS’s highly experienced air testing consultants will visit your site. They will review the design or as-built details and determine if the building is on course to pass its air test first time or if remedial works are required as there are potential risks of an air test failure.

If you are not sure if you need this service, give HRS a call, we are here to help – a call costs you nothing and can save you lots

A highly trained and experienced Air Testing expert will come to your site with fully calibrated and certified kit. HRS are now pointing this out as it has come to our attention that some companies have been carrying out the test using kit that is not calibrated. If the air testing kit is not calibrated or the technician carrying out the air test is not certified to carry out the air test, you will not have a valid test and Building Control will not accept your air test result. HRS are fully UKAS accredited and are founder members of the Air Tightness Testing Measurement Association (ATTMA). With an impressive number of air tests carried out, working on some of the UK’s flagship projects, you can have confidence in HRS’s kit, technicians, consultants and office staff. HRS’s aim is to help you pass your air test first time, on time and within budget.

If you are not sure when you need to call about Air Testing, it is never too early so please give HRS a call and we can ensure you get the right advice at the right time.

At busy times of the year, which are typically March and July/August – if you require a specific test day please contact HRS 5 working days prior to your air test date. If you have fewer than 5 days to your air test date please do contact HRS and we will do our very best to try and ensure that we can accommodate you with the date you require.  

If you need an out of hours air test or temporary sealing, if possible we ask that you give 10 days notice prior to the air test being carried out. Whilst we appreciate this may not always be possible, the reason we ask for 10 days notice is to ensure that there is enough time to scope the works accurately and arrange for any access plant or extra air test equipment that may be required

HRS have air testers based across the country and can usually arrange air tests at short notice. At times HRS have arranged air tests within hours of receiving the call / email, ensuring that our clients achieved their hand over dates. Please do contact us, the HRS team will always do all they can to meet your requirements.

Most air tests to domestic units and simple commercial units are carried out in 30 – 45 minutes which may be extended if the test fails and leakage paths are investigated with smoke. Re-tests can be carried out at no extra charge if completed within the allowed time.

On larger commercial  units, which require 1 large air test fan, air tests usually take 1 hour if all temporary sealing has been completed prior to starting the air test.

If complicated or very large buildings are being air tested with multiple fan units, allow up to 4 hours for the test and longer if smoke investigations are required.

Initially the air test data is checked and verified by the HRS office team, prior to the final result being calculated. Then, the client is sent an electronic PDF version of the final air test report and the result is logged on the ATTMA web site, which can be accessed by clients and M and E engineers in order to verify air test results for use in EPCs and other certification.
smoke-testingSmoke generators or smoke pencils are used to help identify air leakage paths in the case of an air test failure.

On most occasions, HRS highly trained and experienced Air Testing Consultants will be able to locate the problem areas and identify where air is leaking out of the building by walking round the site with a smoke pencil checking the most common problem areas first.

If required HRS can use a fan and a smoke generator to do a full building smoke test, however on 99% of cases HRS find that by using an experienced HRS Air Testing Technician and a smoke pencil, the problem areas can be located.

For clarity as it is a question HRS get asked a lot when carrying out full building air tests, the smoke will cause no damage to the building, however the building does needs to be emptied of all people for Health and Safety reasons. HRS also recommend that the Fire Brigade is informed to avoid unnecessary call outs. The smoke is a harmless food grade water based monopropylene glycol (MPG), but it is a good idea not to expose fresh food or produce to it.

A fan pressurisation unit blows the smoke out through any holes, gaps or cracks in the external building envelope, rendering the air paths visible. Smoke leaking from the building can be seen outside, and photographed to provide a record of external leakage paths.

Smoke tests are ideal for identifying generic areas of air leakage.

Case Studies & Gallery

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Temporary Sealing For Air Tightness Test

What is key to ensure air tests with temporary sealing are effectively organised is to contact HRS early to discuss the scope of works. HRS offer advice to enable a schedule of temporary sealing works which identifies what needs sealing where; the number and size of intakes/extracts/louvres; access required; what materials and equipment are needed and programming the sealing works to coordinate with other site works including commissioning. Failing to adequately plan for temporary sealing usually leads to stress on the day of the air test and failure of the air test.

HRS have teams of temporary sealers with the experience gained on attending and supporting 100’s of air tests on projects nationwide. Most of HRS temporary sealing teams are experienced air sealers as well and can offer smoke testing skills and practical advice on how to carry out remedial sealing.

HRS teams have the relevant training and certification to set up and access scaffold towers, scissor lifts, cherry pickers and where access is particularly difficult rope access. All HRS personnel are provided with body harnesses and lanyards to safely access man safe systems.

HRS teams come equipped with specialist equipment to enable all elements of the building to be quickly and effectively sealed. Equipment can include extendable props, sheet materials – polythene, foil faced boards, COREX, thin plywood and different tapes and glues including low tack variants to avoid damaging finishes.

All mechanical ventilation needs to switched off and in some cases isolated and attendance by the installer is normally required.

HRS temporary sealing teams normally attend and support during the air test itself and are on hand to strip the temporary sealing after the air test is complete.

The air test is a pressure test on the thermal envelope of the building, which should be complete. All intentional ventilation openings including H and V ductwork, louvres, trickle vents can be temporarily sealed. All drainage traps should be filled with water.

Smoke vents are not intentional ventilation openings and should NOT be temporarily sealed. Other elements which should not be sealed are all external doors, windows etc. Please note that if they are sealed this will invalidate the air test and the air tester will note these in the air test report.

Room Integrity Testing

HRS have extensive experience in offering air tightness consultancy, final air testing and air sealing services on rooms with fire suppression systems. Specifications are worked to include NFPA 2001 and BS EN 15004.  HRS have worked on all types and sizes of protected rooms, including server rooms, plant rooms, boiler rooms in offices,  hospitals, data centres, and factories with either gas suppressant or halo carbon gas systems.

HRS use fully calibrated equipment – RETROTEC fans in conjunction with accredited software and technicians to provide a fully certificated service to clients.

On receiving enquiries HRS confirm in detail the specifications to be worked to and the exact scope of the air testing works, including the format of the final report and the certification required.  HRS will define how the test results are to be expressed in terms of hold time / leakage rate  m3/hour/m2 at 10 pascals / peak pressure analysis / results in terms of lower or higher leakage figures.

Room integrity test results are provided immediately after tests and final reports submitted within 48 hours, after the formal checking of air test data.

Room Integrity Testing is in principle similar to a building air test, where a calibrated air test fan with manometers is set up on a door into the room or area to be tested. Ventilation ducts leading out of the test zone need temporary sealing but re-circulation systems and gas suppression systems can be left in operation.  The air test with peak pressure analysis  generally takes 2 hours on site.

HRS experienced technicians use smoke pencils to identify air leakage paths and carry out re tests after remedial works are completed.

HRS can offer experienced air sealing/fire stopping teams to carry out air sealing /  fire stopping (to FIRAS standards) to rectify air leakage paths until Room Integrity Testing specifications are met.

Smoke Testing

If your building fails it’s air test, HRS highly trained and experienced air test technicians will help you to understand why your building has not passed the air test

HRS generally use hand held smoke generators or smoke pencils  to help identify air leakage paths in the case of an air test failure. In special cases, HRS can bring to site a number of high volume smoke generators which can fill large buildings with smoke relatively quickly.

On most occasions, HRS highly trained and experienced air testing technicians  will be able to locate the problem areas and identify where air is leaking out of the building by walking round with the site manager using a smoke pencil to check the most common problem areas first – eaves/verges/plant rooms. The smoke leakage paths can be reported on by a schedule including photographs or video if required.

If required HRS can use an air test  fan and large volume smoke generators with CO2 bottles to carry out a full building smoke test. However, in 99.9% of cases HRS find that by using an experienced HRS air testing technician working with the site manager and a smoke pencil, the problem and risk areas can be identified.

HRS have experience of smoke testing existing buildings to identify air leakage paths, and have  sometimes used thermal imaging cameras to aid the investigation.

It is helpful for the building to be pressurised up to at least 10 pascals with an air test fan to blow the smoke out through any holes, gaps or cracks in the external building envelope, rendering the air leakage paths visible. Smoke leaking from the building can be usually be seen both inside and outside, and photographed to provide a record of air  leakage paths.

Smoke tests are ideal for identifying generic areas of air leakage and proving them to sceptical sub-contractors and clients.

Localised smoke investigations using hand held smoke generators or smoke pencils usually take 1 -2 hours, depending on the size/complexity of the building and the knowledge / experience of the air tester and site manager to identify and access areas of potential air leakage.

Full building smoke tests to large units  can take 4 or more  hours depending on how long it takes to fill the building with smoke and then to evacuate the smoke out of the building.  The investigation phase takes the time to walk the perimeter of the building taking a video to record results.

HRS get asked this question a lot. The smoke is a harmless food grade water based monopropylene glycol (MPG), but it is a good idea not to expose fresh food or produce to it. Please note the smoke will cause no damage to the building or finishes.
The building needs to be emptied of all people for Health and Safety reasons, and HRS strongly  recommend that the Fire Brigade and neighbours are informed to avoid unnecessary call outs and worry.


HRS carried out Passivhaus testing at Interserve LeicesterHRS have worked on a number of Passivhaus schemes, so have extensive practical and technical experience. A Passivhaus project and an award winning building that HRS were heavily involved in is the prestigious Passivhaus Interserve Offices in Leicester.

The HRS Passivhaus air testing consultancy service will ensure you get the right advice at the right stage to achieve the Passivhaus standard. It is crucial if you are working to the Passivhaus standard that you contact HRS early – it never to soon to contact us.

Passivhaus (or ‘Passive House’) is the fastest growing energy performance standard in the world. It is said that the Passivhaus standards strengths lie in the simplicity of its approach; build a house that has an excellent thermal performance, exceptional air tightness with mechanical ventilation.
The objective for a Passivhaus building is that thermal comfort can be achieved solely by post-heating or post-cooling of the fresh air mass, which is required to achieve sufficient indoor air quality conditions, without the need for additional recirculation of air.
Passivhaus is often compared and confused with the Code for Sustainable Homes and BREEAM ratings for non-domestic buildings.  They are not the same: Passivhaus is a specific energy performance standard that delivers very high levels of energy efficiency, whilst the Code and BREEAM are overarching sustainability assessment ratings which address a large number of environmental issues.
No. It is a misconception that the Passivhaus standard only applies to residential dwellings. The Passivhaus standard can also be applied to commercial, industrial and public buildings.
The Passivhaus standard was developed in Germany in the early 1990s by Professors Bo Adamson of Sweden and Wolfgang Feist of Germany and the first dwellings to be completed to the Passivhaus Standard were constructed in Darmstadt in 1991.
There is often confusion over the Passivhaus standard as it can be confused with the more generic approaches to passive solar architecture, as it does shares some common principles.

Where the Passivhaus standard is not the same as the more generic concepts is in Passivhaus’s ability to reduce the permitted space heating demand and primary energy consumption. This means it can be considered as both a robust energy performance specification and a holistic low energy design concept.
Passivhaus thermal comfort is achieved to a greatest practical extent through the use of passive measures. Please see the list below – this can be applied to the residential dwellings, commercial, industrial and public buildings:

  • Good levels of insulation with minimal thermal bridges
  • Passive solar gains and internal heat sources
  • Excellent level of airtightness
  • Good indoor air quality, provided by a whole house mechanical ventilation system with highly efficient heat recovery

There are no strict requirements with respect to domestic hot water, lighting and appliance consumption. The standard imposes an overall limit on the Primary Energy consumption which promotes energy efficiency in all of these areas.

The Passivhaus standard is a comprehensive low energy standard intended primarily for new buildings. The following energy performance targets define the standard and must be met in order for certification to be achieved.

Energy performance targets and air changes per hour
Specific Heating Demand ≤ 15 kWh/m². yr
Specific Cooling Demand ≤ 15 kWh/m². yr
Specific Heating Load ≤ 10 W/m²
Specific Primary Energy Demand ≤ 120 kWh/m². Yr
Air Changes Per Hour ≤ 0.6 @ n50
It is possible to achieve the Passivhaus standard when refurbishing buildings, although this can be a lot more costly.

The standard requires that the Primary Energy demand target is met in all cases, this figure must include the space heating, domestic hot water, lighting, fans and pumps and also all of the projected appliance consumption. In addition to the primary energy demand the standard permits that either the Specific Heating Demand or the Specific Heating Load must be met.
Yes – the energy balance of the proposed building must be verified using the Passivhaus Planning Package (PHPP) using the appropriate regional climatic dataset. Either the monthly or the annual method may be applied.

If the Specific Heat Demand is ≤ 8kWh/m².yr or the ratio of free heat gains to heat losses is greater than 0.70, it is recommended that the monthly method is used to ensure accuracy.

The standard provides limiting backstop values for the glazing specification, ventilation systems, air tightness levels and thermal bridging, as these factors should not exceed these limits in order that the thermal comfort criteria can be maintained.
The following table illustrates the elemental backstop values which should not be exceeded in order for the Passivhaus certification criteria to be met.

Design Component Limiting value
Walls, Roof, Floor (U-values)* ≤0.15 (W/m²K)
Glazing unit ≤0.8 (W/m²K)
Installed glazing ≤0.85 (W/m²K)
Doors ≤0.8 (W/m²K)
Infiltration (ach-1) ≤0.6 @ n50
Thermal bridging (linear ψ value) ≤0.01 (W/mK)
MVHR coefficient (η HR) ≥0.75
Ventilation electric limit 0.45 Wh/m3
Appliances High efficiency recommended
Lighting High efficiency recommended
On site renewables No requirement but SHW typical
* please note opaque U-values are only recommended targets and are not critical to certification.

The backstops above apply to moderate weather regions only, for warmer climates the performance values could be reduced. Please consult your building certifier for more information.
A refurbished building can be certified as a “Quality-Approved Passivhaus” if the certification criteria for Passivhaus are met when refurbishing a building – this is based on the same criteria as for new buildings. It can however be very difficult to achieve the Passivhaus standard for older buildings for various reasons.

If you are able to use Passivhaus technology for all relevant building components in your existing buildings, it will lead to substantial improvement in respect of thermal comfort, structural protection, cost-effectiveness and energy requirements.

If a building is refurbished using Passivhaus components and largely with exterior wall insulation, it can be certified to the EnerPHit standard. This will then show evidence of quality assurance and verify achievement of the specific energy values.
The designation EnerPHit+i is used if more than 25% of the opaque exterior wall surface has interior insulation. It will be likely that moisture analysis will be needed where opaque elements are insulated internally.
The standards have slightly relaxed certification criteria, as indicated below:

Criteria Passivhaus EnerPHit
Specific Heat Demand ≤ 15 kWh/m².yr ≤ 25 kWh/m².yr
Primary Energy Demand ≤ 120 kWh/m².yr ≤ 120 kWh/m².yr *
Limiting Value n50  ≤0.6-1 n50  ≤1.0-1
* PE ≤ 120 kWh/m².yr + ((SHD – 15 kWh/ m².yr) x1.2)
As with new build projects, the energy balance of the refurbished building must be verified using the Passivhaus Planning Package (PHPP). For calculation of the specific space heat demand, both the monthly as well as the annual method can be applied, see the Outline Specifications above for further details.

Plenum Testing

Do you have plenums in your building? If the answer is yes, you need to be aware that a staggering 70% (approximately) fail their first air test. HRS have years of experience of raised access floor plenum air pressure testing and can work with you to ensure you pass your air test first time.

HRS can ensure that an air test site advice visit is arranged as soon as the floor is in place, we can then assess your design and offer you specification advice to ensure that your plenums are adequately sealed.

A plenum is part of a building that normally facilitates air circulation for heating and air conditioning systems by providing pathways for either heated/conditioned or return airflows, usually at greater than atmospheric pressure. Typically this is under a raised floor or between the structural ceiling and the suspended ceiling.
70% of plenums fail their first air test as there is still a lack of understanding within the construction industry as to how airtight a plenum needs to be. Often people are working on information about plenums that have been tested in a lab under laboratory conditions, and as everyone that has worked on a construction site knows, there is a big gap between what happens in a lab to the reality of plenums on a construction site. With multiple contractors needing to put pipes, cables etc through the plenum, this is just one of many things that can affect the air tightness of a plenum. HRS have years of experience and can work with you to ensure you pass your air test first time.
HRS plenum desktop and on site design reviews assess how elements of the plenum are specified and how they are integrated together to form a workable plenum.
In brief, a tile is removed from the plenum for a celotex tunnel leading to the HRS fan.

Any air handling ducts serving the test zone need to be turned off, isolated and temporarily sealed, stopping the passage of air to outside of the test zone via ductwork. Once the area has been prepared and the fan set up, the test takes place in the same way as a HRS normal air pressure test, i.e. taking a number of pressure readings over a period of about 30 to 45 minutes.

If your air test fails, your HRS air tightness technician will carry out a smoke test to look for air leakage paths and sometimes it is possible to carry out remedial works.

At present there is no set standard for plenum testing. The specification is usually set by the project’s Mechanical Engineers, and is normally set in litres per second per square metre (l/s/m2). HRS will need to know what pressure the specification is set at, e.g. 0.5l/s/m2 @ 50 Pascals. It is possible that the specification can be set in l/s/m3 and for this HRS would require the volume of the RAF Plenum.
If your plenum has failed, don’t panic! HRS have extensive experience of carrying out plenum remedial works (when we have not be contacted at an early stage, to give the help and advise that is needed).

HRS’s practical and technical expertise means we can identify defects/problem areas and carry out the necessary remedial works.

HRS can provide you with a complete range of building environmental and sustainability services, meaning you can save time and money, avoid inconvenience and your risks are minimised.

From concept design stage to completion, HRS can work alongside you every step of the way. You and your project would be supported by HRS’s extensive knowledge that has been built up over 30 years, whether you need consultancy or on site advice and guidance, HRS’s large team of consultants and on site technicians are here to support you to make sure that your project hands over on time and within budget.

At HRS we believe strongly in being pro-active and customer focused, providing you with innovative cost-effective solutions.

All you need to do is make one phone call to 0800 030 4391 or email: sending one set of drawings stating what services you require, and HRS will take it from there.

Building and Enviromental Services from HRS

0800 030 4391

Knowledge Hub
“Just wanted to drop an email show appreciation for HRS operatives for the works that they carried out. They very knowledgeable and were able to guide and work with our site team,  in order to achieve satisfactory air tests.”
Project Manager, Kier Construction
“Please pass on my thanks to the air tester for there positive approach and his hands on attitude. Can you please also pass this on to his line manager in his professional attitude. I look forward to being able to use HRS again in the future.”
Quantity Surveyor, Morgan Sindall
“I would like to thank your air tester for his patience during the past tests. He has given me excellent advise which we help on future projects.”
Design Co-ordinator, Balfour Beatty Construction

Relevant Accreditations

To see the wide range of accreditations that HRS Services hold, please visit our Accreditations page »

Need advice or a quotation give HRS a call on:
0800 030 4391 or email: