FAQ: Heat Recovery Ventilation

Q. Should every house have a HRV System?

A. It depends on the house. There would be no benefit to installing one in an old house with ‘natural’ draughty ventilation. However, if you are renovating an old house and intend to seal it and insulate it, then it is recommended.

Q. Do I still need a heating system if I am using a heat recovery system?
A. Yes. HRV is not a heating system, it’s a ventilation system. It recovers the heat you would ordinarily loose through natural draught ventilation, wall grilles and trickle vents etc.


Q. Does it work with all types of heating systems?
A. Yes, it works independently of your heating system. The unit recovers the heat from the warm air in the house. It doesn’t matter how that heat was generated, whether by oil, gas, wood pellet, electricity, heat pump or any other source. However, it is important to choose a heating system that will suit your needs.


Q. What are the benefits of Heat Recovery Ventilation?

A. The following are some of the benefits:
1.    Your home will have a constant supply of fresh air with higher comfort levels.
2.    Overall air quality within the house is significantly increased which is of benefit to all occupants especially Asthma & Hay Fever sufferers.
3.    No condensation.
4.    No fungal growth in bathrooms.
5.    Fresh smelling bathrooms (air is constantly being changed no need for air freshener).
6.    Less dust (windows are kept closed and all air in to house is filtered) less spiders as they feed on dust mites.
7.    Extra security (windows closed no need to part guard alarm).
8.    Quieter house less outside noise as windows are kept closed.
9.    Lower heating bills.
10.    Wake up feeling refreshed instead of groggy (due to lack of oxygen).

Q. What will I see in each room?

A. You will see a supply air or an extract air valve in each room. It is through these air valves that the fresh filtered air is supplied or stale air is taken away. 


Q. How will I know when to change the filters?
A. An indication light will automatically switch on when the filters are due to be changed.

Q. How often do I have to replace filters?
A. Under normal conditions it is recommended that the filters be changed every 6 months.

Q. Can I change the filters myself?

A. Yes. It is very simple you just open the front cover and the filters just slide in & out.
Full directions are given in the operator manual supplied.

Q. Is the HRV system noisy?
A. The Flaktwoods HRV system is extremely quite. The HRV unit is acoustically lined. Silencers are installed in the ductwork to reduce whatever noise there is. At the end of the installation process the system is balanced resulting in a very quite system. You will hardly notice the system working in the background. See the Flatwoods brochure for decibel levels.



Q. How much does it cost to run?
A. It depends on a number of factors – how the unit was sized, the size of the house, the design of the system and the type of ductwork used. While the unit does use a small amount of electricity, the amount of energy saved greatly out-weighs the amount used.

Q. How often should the unit be serviced and what maintenance is required?
A. The unit should be checked every year. Basic servicing can be carried out by the owner. In order for the system to work correctly and effectively it is important that approved maintenance procedures are followed. The main component of maintenance is filter changing. Details on servicing of the unit are contained in the user manual.


Q. Can I turn the unit off?
A. It is recommended that the system runs continuously. This will help keep the air fresh, avoid a build-up of smells, moisture etc. and reduce the risk of condensation in the ducts.

Q. What can I do to keep the house cool in the summer?
A. The Flaktwoods RDAR & RDKR units come with an automatic summer bypass. The RDKG & RDAB units come with a manual summer bypass. The summer bypass prevents the heat being recovered from the house while still supplying fresh ambient air moving throughout the house thus giving a cooling effect.


Q. Where can the unit be installed?
A. Generally the unit is installed in an attic space, utility room, basement or adjoining garage. Some models are suitable for fitting in a cupboard or hot-press within the kitchen or another room.

Q. Where are the controls located?
A. The main control unit is normally located in the kitchen or utility room but can be located anywhere in the house to suit you.

Q. Do I need wall and window vents?
A. No. The house should be as airtight as possible. You will be getting a constant supply of fresh air into your house through the HRV system.

Q. Can this unit be fitted to an existing building?
A. Yes, provided there is a sufficient level of air tightness. Bungalows are quite straightforward while two-story houses & dormer houses require additional building work. 

Q. What happens in a power cut?
A. In a power cut the unit will not operate, this however will not have any immediate effect on you or your house. Most power cuts last only one or two hours and as the ducts are open to the elements there will still be a small air flow. The unit re-starts automatically when the power comes back on.



Q. Where does the steam from the shower go?
A. There is a condensation drain on the back of some of the units which is connected to a waste water pipe or can be plumbed separately to outside if required. In the units with a Rotary Heat Exchanger a drain is not required.


Q. What size is the unit?
A. The physical dimensions of the various units differ. The important consideration in regard to locating the unit is if it will fit through the door or attic hatch and secondly will it be accessible for maintenance and filter changes. The dimensions of each individual unit are available from the Flaktwoods brochure.

Q. How does it work?
A. The principle behind heat recovery ventilation is to change the air continuously in the house and use the recovered heat to warm the incoming air. Extract points are located in wet areas such as bathrooms, kitchen, utility and WC. Supply points are in areas such as bedrooms, living and dining rooms. The RDKR and RDAR Units come with a high efficiency Rotary Heat Exchanger and the RDKG and RDAB Units come with a plate heat exchanger. The heat exchanger transfers most of the heat from the extracted “wet” air to the incoming fresh air.

Q. Can I do part of a house?
A. It is recommended that the whole house is served by the system.

Q. In the course of building what steps should be taken to ensure that a HRV system will work well?
A. The house should be well insulated and well sealed. This means that there will be minimum heat loss and the air flow through the house can be controlled. (A well insulated house may not necessarily be airtight). Air can easily pass through insulation made from coconut, mineral or glass wool. An airtight house may not necessarily be well insulated: e.g. excellent air tightness can be achieved with a single aluminium foil but it is not an insulating material).

Q. What are the Health Benefits?
A. On average most people spend over 80% of their time indoors. 50% of all illnesses are either caused by, or aggravated by poor indoor air quality. The HRV System will continuously remove stale moist air from your home creating a more suitable and healthy place to live.

Q. What size of heat recovery unit will suit my house?
A. The Flaktwoods RDKG or RDKR unit will serve houses/apartments up to 155 m2 approx. The Flaktwoods RDAB-01 or RDAR unit will serve houses from 156 m2 up to 280 m2 approx. The Flaktwoods RDAB-02 or RDAR unit will serve houses from 281 m2 up to 370 m2 approx. Houses bigger than 370m2 can be served with a combination of HRV units. See the Flaktwoods brochure for more details.

Q. How efficient is the unit?
A. The efficiency of any heat recovery ventilation system will depend on a number of factors including the size of the unit installed, the size of the system/house and the type of heat exchanger in the HRV Unit. Please see the Flaktwoods brochure for further details on efficiencies.

Q. How do I get an estimate?
A. You can contact us at our office. Forward a set of drawings and you will be contacted within a few days.

Q. At what stage in my build should the HRV system be installed?
A. The ideal stage to install a HRV system is at 1st Fix (Carpentry). It is important that the ductwork is installed prior to slabbing or insulating of internal partitions or ceilings as this may hinder the installation of the ductwork.

Q. What sort of duct is used?
A. Rigid PVC duct is used. This 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 and life span of the system.

Q. Can a HRV System be installed with flexible ducting?
A. 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. It will also make it very difficult to clean if the situation arises.

Q. Are the ducts insulated in the attic?
A. All ducts in the attic are thermally insulated in order to (i) eliminate the possibility of condensation happening inside or outside of the ducts and (ii) avoid heat losses in the attic.

Q. What size ducts are used?
A. The duct sizes are determined based on the volume of air they have to carry and the distance it needs to be carried and also where the duct needs to fit. All duct used in our systems is smooth rigid duct.

Q. Can the extractor fan over the cooker in the kitchen be ducted into the heat recovery system?
A. Your cooker hood extractor fan will not be connected to our system. It could lead to an accumulation of grease etc throughout the system.

Q. What is air-tightness?
A. Air-tightness is the control of airflow through the external envelope of the building. In an airtight building air leaks do not occur at ceiling or wall junctions, plaster board joints, doors, windows, service entry points etc. Leaks create discomfort and heat is lost. The result is that the heating system has to operate at a greater capacity to compensate for the losses.

Q. What are the settings on the switches?
A. Low speed: Suitable for when the house is unoccupied or when on holidays.
Medium speed: Use this setting for normal everyday use when the house is occupied.
High Speed: This setting can be used when there are a lot of people in the house (Also known as party mode).

Q. Is there any condensation drip pipe?
A. With the RDKG & RDAB units there will be a certain amount of condensation. Any water that condenses in these units is drained off through a condensate drain. There is no condensation from the RDKR and RDAR units as they use a rotary heat exchanger. An added benefit of this type of unit is that it does not dehumidify the air in your house to the same extent.

Q. Can I have a fire place in my house if using heat recovery ventilation?
A. In the current regulations guidance document Part L it is recommended that any fuel burning appliance should be in excess of 86% efficiency. An open fire is estimated to be about 20% efficient. When the fire is burning, air is being taken from the room and by convection goes up the chimney. This causes negative pressure in the house. As a result, cold air will be sucked in as soon as a door is opened. The combustion air for any fuel burning appliance must come from the outside (A natural permanent vent is required). This can be achieved by fitting a duct under the floor or directly through a wall (if the fireplace is on an outside wall). With some fuel burning appliances the combustion air can be supplied down through a specially built balanced flue chimney.

Q. Is it ok to have a free standing stove and a HRV system in your house?
A. Yes, but remember the stove will need an independent external air supply (A natural permanent vent).

Q. How should a gas fire be connected up?
A. Gas fires should be of the enclosed type. These can be fitted with a balanced flue down through the chimney. Section J of the Building Regulations state that any fuel burning appliance must have a permanent external air supply available to it. By this, they mean a hole in the wall or a balanced flue as described above.