How to Size Heat Recovery Ventilation System

How to Size Heat Recovery Ventilation System

How to Size Heat Recovery Ventilation System

Installing a heat recovery system isn’t as straightforward as you think. Especially if you’re new to installing a system, you need to know how to size a heat recovery system.

But how exactly do you do that? Can anyone do it? This blog has all the answers and more.

With new buildings being made to be as energy efficient as possible, and the UK aiming for 95% of its electricity usage to be low carbon by 2030, it is imperative to understand how we can make the most of our ventilation. This is where MVHR units come in.

To prevent mould, fresh air should constantly be introduced into your dwelling daily, as it helps to regulate temperature and reduce condensation. Introducing fresh air can be as simple as having a ventilation routine, or installing extractors or MVHR units. Almost all of this is facilitated by ducting.

Does every home need ventilation?

Yes, every home requires ventilation. Without ventilation in your home, air can become stale, humid, and full of dust and allergens. That being said, not all ventilation is mechanical. Simply opening your windows is a form of ventilation.

The downsides to opening a window is the risk of cold, or bad weather entering the home, as well as bugs. This is why a ventilation system can benefit almost everyone greatly.

Additionally, advancements in technology have allowed the development of systems that can ventilate and clean the air you breathe, whilst preventing it from getting cold, like it would from opening a window.

This is achieved by a heat recovery ventilation system.

What is a heat recovery ventilation system?

What is a heat recovery ventilation system?

A heat recovery ventilation system is an advanced form of a ventilation system. It is known as MVHR, which stands for ‘Mechanical Ventilation with Heat Recovery’,

Its advancement is characterised by the fact that it can retain the heat in the space it ventilates, whilst simultaneously filling the home with filtered outdoor air. MVHR units are available as a single or a multi-room unit.

Single room MVHR units are ideal for bathrooms or kitchens, whereas whole house units are appropriate for any home, as long as the home is appropriately insulated, you will feel the full effects of the MVHR unit.

Whether your home is new or old, MVHR is a win-win. Your home will feel comfortably warm, whilst also combatting the environments that mould thrives in. You gain the benefits of having fresh air, an environment with a reduced level of allergens, and peace of mind that you’re saving money on energy bills in the long-term.

The benefits provided by the system pale in comparison to the comfort you have knowing that mould will struggle to grow in your home. Mould can seriously affect anyone with an allergy to it, along with those with a compromised immune system.

MVHR benefits

The benefits of heat recovery systems are the following:

  • Temperature sensors ensure that additional heat is not being added to the atmosphere of the home if it is already hot.
  • Heat recovery systems take a lot of the burden from you conducting a ventilation routine. This is ideal for a vulnerable person.
  • Less of a need to use your central heating frequently as the heat generated through your house is recycled through the heat recovery unit.
  • The reduced use of heating as a result of the heat conservation granted by a heat recovery unit can help you save on energy bills.

How to size heat recovery ventilation system

How to size heat recovery ventilation system

To size a heat recovery ventilation system, you must conduct a full airflow calculation of the dwelling. This calculation must result in at least 0.3 litres per second per metre squared of floor, as this is the minimum required airflow in accordance with Part F of UK building regulations.

As a result of this, you can then select a MVHR unit, and appropriate ducting that can deliver the airflow requirement.

But what does that mean? What is the reason for it?

Put simply, ‘sizing’ a heat recovery ventilation system, is the process of selecting the correct MVHR system and ducting for a dwelling. With MVHR, there is no ‘one size fits all’ method of application.

If you end up with a MVHR unit that is too small, you may struggle to get the appropriate airflow into the dwelling. Whereas, if your unit is too big for the dwelling, you may find that you are getting the results, but at the cost of paying more than you realistically needed to.

Who can size a heat recovery ventilation system?

It is advised to consult somebody who is a HVAC contractor. This is someone who can be  well versed in not only installing MVHR, but picking the right one, with the complimentary ducting, for the dwelling.

You can go to your local builder, who could definitely install it, but without the expertise of a HVAC contractor, your MVHR system may not work as effectively as it should.

What is MVHR commissioning?

MVHR commissioning is the process of having your MVHR system tested to ensure it is balanced. MVHR systems operate differently depending on the dwelling they are placed in, as well as the size of the rooms and more, which is why commissioning is required.

MVHR commissioning can be carried out by HVAC contractors.

How much are heat recovery ventilation systems?

The cost of MVHR systems vary between the type of MVHR unit you need. Naturally, single-room units will cost less than whole-house units. Our range of MVHR units begin at £262, all the way to £2895.

Below we will share some information on our most cost-effective single room, and whole house units. You can click here to view our full range of MVHR units.

Single room unit – Kair Heat Recovery Extractor Fan – 12VAC SELV – Humidistat

At £299.94 The Kair Single Room Heat Recovery Ventilator is perfect for you if you are looking to solve a damp problem in one of your rooms. Such as your kitchen, bathroom, utility room, living room, lavatory, washroom, conservatories, office, and bedroom.

The unit also offers continuous trickle ventilation, meaning it will constantly clean and purify the air you breathe. Continuous ventilation is key to keeping your home mould free.

Nuaire Mrxboxab-ECO3 High Duty Wall Mounted Heat Recovery Ventilation Unit With Bypass And Integral Humidistat

At £2,138.40 , This whole house unit provides the most effective, balanced supply and mechanical extract ventilation with heat recovery, with an automatic summer bypass as standard. 

This unit recovers up to 95% of heat which would otherwise be wasted, whilst also reducing power consumption. The unit is an ultra-quiet unit with a long life motor, which makes for low running and operating costs, straightforward maintenance and years of trouble-free operation.

Purchase a Heat recovery ventilation system today

Purchase a Heat recovery ventilation system today

We at I-Sells endeavour to ensure our customers have all the information they require before investing in our mould solutions. Be sure to visit our blog page to learn about the vast array of factors and issues surrounding ventilation, mould, condensation, and much more.

We hope to have shown you ‘How to size a heat recovery ventilation system’

We understand you may have more questions, do not hesitate to contact us for more information about whatever you need our help with. If you’d like to email us, click here. For other contact options, see below:

Call us on 020 8463 9696

Visit us at our showroom:


Monday – Friday: 8:00 am to 5:30 pm

Saturday: 9:00 am to 12:00 pm

Sunday: Closed

15 St John’s Parade

Sidcup, Kent

DA14 6ES

United Kingdom

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