In a new-build or deep-renovate, installation of our heat recovery ventilation system is a relatively simple process, especially for our highly trained and experienced installation teams.

The air handling unit is best located within the thermal envelope of the house such as in the utility room. Rigid ducting runs from the unit location via distribution boxes through the walls, floors/ceilings to points in each room where air is either supplied or extracted.

See Examples of ducting installations at first fix stage below;

ProAir Duct under hollowcore
ProAir Duct
ProAir Distribution Box
ProAir Distribution Box
ProAir Duct
ProAir Duct
ProAir Duct
ProAir Duct


All rooms are served with either extract or supply and the locations of these air-terminals are selected with some care. Extract points are generally located close to sources of moisture, like showers and cookers. The correct design of supply points is crucial to the effectiveness of the system and contributes to the comfort of the occupants. As air from a Heat Recovery Ventilation system is at a temperature just below that of the house (typically 18 to 20°C) it can feel cool as your body temperature is at around 37°C and for this reason, the air distribution design is important. Typically supply valves should not be positioned directly above locations where people are sitting or sleeping.

When you walk into your newly finished home, the only evidence of the system will be a small ceiling disc in the ceiling or at high-wall level in each room and a fresh living atmosphere.


Where is the unit best located?

The system will work best if it is located within the thermal envelope of the house. You should aim

  • (i) to have it on or near an external wall so that the duct runs to the outside will be short and
  • (ii) to have easy access to it for maintenance. This points to the best location being a utility room, wardrobe or hot press. View here to see a ProAir 600LI unit installed in a utility room.

The utility room is generally on the ground floor which makes it the preferred location if possible. In many houses the ground floor has a bigger area (and volume) when compared to the first floor. This implies that the unit will be located on the floor with the bigger volume thereby needing less electricity. In a utility room there is likely to be easy access to a waste pipe for the condensate from the unit. If space is not available within the thermal envelope the alternative maybe the attic/loft.

Are there other methods of supplying / extracting air from the house?

If the FEX terminal is not an option then the fresh and exhaust vents should be located at 3m or more apart. Avoid soil pipes, extracts from cookers and exhausts from oil/gas burners. This is to ensure that the exhausted/contaminated air is not used as supply air to the system. There are 3 options:

  • (i) Go through opes in the gable using grilles on the outside.
  • (ii) Have the extract and supply come through grilles on the soffit.
  • (iii) Use roof vents and have the roofer install them. They are G5 (150mm) slate vents.
What size is the unit?

The ProAir 600LI unit measures 1025mm (Length) x 680mm (Height) x 485mm (Width). See here. Space needs to be left above the unit so that ducts can be connected.

We will have an extractor fan over the cooker in the kitchen. Can this be plumbed into the heat recovery system?

This fan should not be connected to the HRV system. It could lead to an accumulation of grease etc. throughout the system. It should be ducted to the outside directly unless you are using a carbon activated cooker hood filter.

Where are the controls located?

The main control is located normally in the kitchen or utility room with boost switches outside the wet areas. The unit can also be mounted directly on the PA 600LI unit.

Can the air loss through the cooker hood be minimised in any way?

A mains operated damper can be installed. It is open when cooking is in progress and at all other times it is closed. It is important to take this into account when making decisions on cooker hoods as air tightness in your house would be compromised if no damper is installed. ProAir can supply a mains operated damper on request.

What sort of duct is used?

Rigid plastic oval duct is used. We design the ducting system incorporating distribution (manifold) boxes, so as to optimise air flows etc. Oval duct is more robust than flexible duct and ensures that less power is required to move the required volume of air. Rigid ducting offer less resistance than flexible duct. This contributes to the overall efficiency of the system. See here for more info on design.

Can the system be connected to my fire alarm system?

As a safety feature we can provide a connection for your fire alarm system to the HRV unit.

Can a HRV System be installed with flexible ducting?

We strongly recommend that rigid ducting be installed at all times. Flexible ducting creates too much resistance to air flow and will lower the efficiency of any HRV unit.

How do you find out how air tight a house is?

The level of air tightness in a building is measured by doing a blower door test. A large fan is installed within a temporary door frame in an external door opening and inducing a pressure differential. The test usually involves a combination of depressurising and pressuring the house to a pressure difference of 50 Pascal’s (50Pa). (A pressure difference of 50 Pa can be compared with the equivalent pressure induced by a wind speed of approximately 22mph on a building). The pressure imbalance between inside and outside of the building forces air through all holes and penetrations in the building. The resulting pressure differential between inside and outside the building is measured. By measuring the airflow through the fan and its effect on the air pressure in the building, the air tightness of the entire building envelope can be measured. It is non-destructive.

Can the system respond to changes in humidity?

Humidity sensors respond to changes in the humidity of the air. Many HRV systems have sensors located in the air handling units. These therefore can only respond to changes in the average humidity of the air coming into them from wet rooms. They do not respond to individual changes in wet rooms. (Having individual sensors in rooms would be very expensive). The ProAir unit uses a maintenance free boost switch. It is controlled by the user. Once the boost switch is pressed the unit will work at high speed for a period of up to 16 minutes to clear moisture from wet areas and then revert to normal operation.

Are the ducts insulated in the attic?

All ducts must be within the thermal envelope of the house in order to eliminate principally heat loss. All exposed ducts running in attics will have to be insulated. Normally the insulation being provided as part of the attic insulation will suffice. There is no need to insulate ducts that are within partitions, under first floor etc.

Do I need wall and / or window vents?

No. The house should be as airtight as possible. This will ensure that all the air is taken in and out through the Air Handling Unit only.

What will I see in each room?

Immediately after installation you will find the oval rigid duct that will bring the air in or out of the room. It will be visible underneath hollow core/timber floor/ceiling joists or over ceiling joists. See here. When plaster boarding, second fix etc. is completed you will find a supply or extract terminal. See here. These fittings have an adjustable centre disc which is used to balance the system. The supply valves are designed to spread air horizontally across ceilings so that downward draughts are minimised. The system is tested and balanced by our technicians and will need no further adjustment.

What size ducts are used?

We use high quality oval rigid ducts. The main types used are 115mm x 60mm (10 Series) and 150mm x 60mm (15 Series). See here for more information about ProAir’s Duct and Joint ducts. These can be used under hollowcore/concrete floors. Likewise they can be used in timber partitions.

It is important that the correct size of duct is installed. Reducing duct sizes to save cost is false economy. It is likely to create noise and impact negatively on the running of the air handling unit. In many instances small round ducts will not permit the easy passage of the required air volumes. If a certain volume of air per hour is required more electrical power is needed when using small duct. In some cases a second small duct may be required. The most commonly used ProAir D&J ducts 115mm x 60mm and 150mm x 60mm have cross sectional areas corresponding to circular ducts whose diameters would be 88.3mm and 102.3mm respectively.

A round duct with a diameter of 63mm has a cross sectional area of 3,119mm2. This is just 50% of the ProAir D & J 10 duct. The 63mm duct was designed for the mid-European apartment market where the climate is drier, the runs are shorter and the airflows are lower in multi-story high rise blocks. In Ireland and the UK we have a damp maritime climate. Our HRV systems need to be carefully specified and designed so that the right amount of air gets to and from the right places with the least pressure on fans. Low airflow will lead to condensation and possible mould growth. High pressure on fans will lead to shortened lifespans and higher electricity bills.

See here for duct size comparisons.

At what stage in my build should the HRV system be installed?

The ideal stage to install ProAir ducting is at 1st Fix. We like to be the first ‘first’ fixer. We go to all the rooms in the house.

What is the best way of getting fresh air into and out of the house?

ProAir Systems have designed a FEX terminal that facilitates the ingress and egress of air to and from a MVHR unit. It ensures that no cross contamination of the Fresh and EXhaust airflows occurs as they enter/leave the building. It also means the duct runs to the outside are kept as short as possible and improves the efficiency of the HRV system. The FEX Terminal is proprietary to ProAir Systems that is Patent Pending. The terminal has been independently tested by the Centre for Sustainable Energy of Galway Mayo Institute of Technology (GMIT). It is normally installed as part of ProAir’s installation. It is also available for sale directly from ProAir Systems. See here for a datasheet.