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What is Heat Recovery Ventilation?

heat recovery ventilation

When we started designing and supplying heat recovery ventilation systems the main reason to have a heat recovery system was to recover the heat normally lost through the conventional bathroom extractor fans and air supply vents built into the windows and walls in every room and a heat recovery system achieves this very well with recovering over 90% of the normally lost heat.

But a heat recovery system does so much more and is now more important than most other systems you will be installing into your home!

  • Improving the indoor air quality by filtering all the incoming air
  • Prevents mould and condensation
  • Provides natural cooling in warm weather by supplying fresh filtered air
  • Removes bad odours
  • Helps with asthma and other health issues
  • Distributes heat evenly throughout your home
  • Eliminates the need for bathroom extractor fans and window air vents
  • Complies with all building control regulations
  • And of course, recovers up to 90% of your normally wasted heat

Building control and legislation?

Over the last decade there has been increasing demand on builders, architects and government legislation to increase the thermal efficiency of our homes making them draught free and well insulated. This in turn has caused poorer air quality which can significantly increase the effects of asthma and other respiratory problems, health problems, condensation, mould, dust mites, unpleasant smells and build up of toxic gases.

For health reasons Government legislation now makes it almost compulsory for your new air tight home to have a balanced mechanical ventilation system and a heat recovery ventilation system is the most preferred option.

How Does MVHR Work?

A ventilation system with heat recovery (HRV) or (MVHR) is an energy efficient, controlled and balanced ventilation system. It extracts the moist, stale air from all the wet rooms in your house and replaces it with filtered, fresh, recovered warm air to all your habitable rooms and bedrooms without letting the heat escape.

Your home is fully ventilated throughout the year with as much as 95% of the normally wasted heat being recovered providing you substantial energy savings. This heat recovery ventilation allows your property to stay air tight with no window vents or bathroom extractors being required, creating a healthier and quieter environment.

Can you install heat recovery ventilation to an existing house?

It is possible to install to an existing house, but good planning and design is critical, If your house is a bungalow the installation would be very easy as all ductwork would be in your attic space but if your house has a number of floors we would have to work with you to provide solutions to drop ductwork to the rooms below through service voids like wardrobes and storage rooms

Can you install in a period house with normal levels of insulation?

We have installed systems to a lot of period houses and even a castle, you will not be able to achieve the maximum heat recovery rate of 90% but you will achieve almost all the advantages including fresh filtered air and condensation control


MVHR Ducting Solutions

A heat recovery ventilation system is only as good as the ducting used.

Warmth supply the most comprehensive range of quality ventilation and duct solutions and we can design a system to suit any type of property.

There are two types of ducting solutions:  The Radial System or the Branched System

heat recovery ventilation

Radial ducting is the latest innovation on ventiliation systems and can provide a quieter and more efficient ventilation system compared to rigid ductwork.

Radial Ducting is a system of smooth bore pipes which are crushproof, semi flexible with zero air loss. The pipes have an anti-static and antibacterial lining which individually connects each room to a manifold and are available in both circular (75mm or 90mm) and oval (51mmx114mm) fittings. Radical ducting is suitable for any type of property; including timber framed houses, passive house approval homes and can be used in areas with limited access.


  • Zero air leakage ductwork (pipe ends are mechanically fitted with rubber seals)
  • Low air resistance
  • 50 percent faster installation rate than traditional branch systems (PVC/metal)
  • No crosstalk between rooms (Quieter)
  • Smaller pipework than tradtional branch systems
  • No sealants required
  • Hygenic smooth inner surface
  • Easy to install
  • Easy to clean
  • supplied in 50m coils
  • crushproof up to 16 Kn/m
  • SAP appendix Q recognised
  • Up to 85% less connections than traditional Rigid Ductwork
  • Suitable for DIY installation
  • Installation recommended below loft insulation to improve heat retention compared to older systems

Do not confuse this ducting with flexible or semi rigid aluminium ducting

heat recovery ventilation

Rigid/branched ducting is commonly used and is a cost effective ductwork solution on ventiliation systems.

Is a system of round or flat PVC or EPE rigid ductwork which are typically 150mm or 125mm which branch out with T-pieces into various rooms. PVC Rigid ductwork has been used for over 50 years in domestic installations.


  • Available from 100mm to 300mm diameters
  • Cost efficient
  • Excellent air flow rates
  • PVC range suitable for DIY installations
  • Suitable for exposed locations
  • SAP appendix Q listed
  • Can be commercially cleaned
  • Galvamised metal suitable for traditional systems
  • Installation above the loft insulation and insulated seperately is recommended
  • Galvanised metal has high crushability
  • PVC rectangular range available for areas of limited height.

Heat Recovery Ventilation FAQs

Does a heat recovery ventilation system save me money? 

Heat recovery ventilation systems are designed to recover on average 90% of the heat normally lost through open windows, trickle vents and other break-out points i.e extractor fans. The systems will through time, off-set the heating costs and reduce energy bills, making it a worthwhile investment.

You could lower your heating costs by up to 30% against using window trickle vents and bathroom fans and improve the indoor air quality with fresh filtered air.

Will the indoor air quality in my home be improved with a heat recovery system?

There is a direct connection between the quality of air (caused by poor ventilation) and our ability to concentrate and perform productively, as well as the effects poor indoor air quality has on asthma or allergy sufferers. The heat recovery ventilation unit filters the incoming air to remove pollutants and insects and provides the constant supply of clean, fresh, warm, filtered air reduces symptoms for asthma and allergy sufferers.

Can a heat recovery ventilation system be installed in my existing home?

Yes, this is possible.

With the use of Radial ductwork which is semi rigid and only 75mm in diamater, any installation is possible subject to available space. You can also look at the possibility of installing a system to only the first floor that normally stops any mould and condensation to the 1st floor bathrooms and bedrooms (the most affected areas).

How often do I need to change the heat recovery system filters?

Depending on your house location, the filters usually only need to be cleaned or changed every 6 months to a year.

Warmth also have a range of filter media that can provide a cost efficient option of less than £10. If the filters are no longer available for your unit or the OEM are too expensive you could fit a filter box each side of the unit and a filter change could cost less than 20 per year.

What’s the guarantee on heat recovery ventilation systems?

Our heat recovery ventilation systems are covered by a 1 year to 5 year parts and labour warranty depending on unit.

Vent Axia have a basic one year parts and labour and a further 4 years parts only.

How much does a heat recovery ventilation system cost?

The cost depends on the size of house, the number of extraction and distribution points required, and the air volume rate required for the house that determines the size of unit. We will design a bespoke system for each and every house with the choice of various available units to suit your budget and property.

Is a heat recovery system expensive to run?

With the newest generation EC low energy fans fitted, running costs are very low and are approximately the equivalent of a light bulb to run.

The main part of a heat recovery ventilation system is the counter flow heat exchanger which itself requires no power, the only power required is for the small fans to push the air around the house, power usage is very minimal and average annual cost can be as low as 20 to 30 and as most units recover on average 90% of the normally wasted heat any expenditure is easily offset

How can I ensure compliance with current building regulations with a heat recovery system?

All our systems are designed to comply with all building regulations and help improve SAP / BER ratings. It is required by Building Control to have the ventilation system commissioned, a service provided as standard for all installations by Warmth.

When we provide a proposal or plan we can provide airflow rates that will satisfy building control.

What is SFP on a heat recovery system? (Specific Fan Power)

SFP (Specific fan power) is the amount of energy required measured in watts per litre of air per second (L/s) and is used in the industry to measure the power efficiency of the heat recovery unit (if you use 30 L/s of air with a vent axia kinetic @ 0.5 SFP you would only use 15 watts of electricity)

Simply, the lower the SFP, the better the energy use of the unit. Also the better the % of heat recovery the more heat is recovered.