Do All MVHR Systems Require a Defrost Unit?

Do All MVHR Systems Require a Defrost Unit?

Do All MVHR Systems Require a Defrost Unit?

Unbeknownst to some, your MVHR unit has the capacity to be affected by freezing temperatures, this can result in a reduced efficiency, or even serious technical issues for your MVHR unit.

With that being said, is there anything that can prevent it? Either within or separate from the MVHR system?

In this blog, we will address the question ‘Do all MVHR systems require a defrost unit?’

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.

Do you need ventilation in cold weather?

Although a winter breeze is generally less pleasant than a summer’s breeze, you should know that regardless of the time of year, ventilation is needed in your home all year round.

Neglecting ventilation on hot days can result in a home that is uncomfortably hot, the air can also become stuffy and stale. When it comes to cold days, humidity and condensation develops at a faster rate in an unventilated hot home, simply due to the contrasting outdoor temperature.

As a result of neglecting ventilation on a cold day, the dwelling in question may end up being susceptible to mould growth.

Mould is a potentially dangerous form of fungus that thrives in humid environments, it can develop in any room, but is commonly found in bathrooms and kitchens. Mould has the potential to cause or exacerbate health conditions. It should be removed wherever possible.

How do I prevent mould in my home?

Common methods of mould prevention in a home can be achieved through the following suggestions…

  • Opening windows regularly, especially in bathrooms and kitchens when you are using them.
  • Invest in, or update, your extractor fans/MVHR systems.
  • Remove any existing mould in the home.
  • Address any issues that can cause mould, like leaking pipes, or unsecure windows and doors that let drafts into the home.

What is MVHR?

MVHR stands for ‘Mechanical Ventilation with Heat Recovery’. This is the formal term, the units that use this technology are generally known as heat recovery units, or heat recovery systems.

As the name suggests, MVHR units provide the function and benefits of ventilation, whilst also finding a way to recover heat that is lost during ventilation. They are available in single or multi-room units.

The advantages 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.

Do all MVHR systems require a defrost unit?

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There may be exceptions, but in areas in which cold climates are frequent, MVHR units would require a defrost unit. If the area in which you live regularly experiences temperatures in the minus, a defrost unit is essential.

Luckily, most modern MVHR units have a defrost unit, or functions that help to prevent any issues that could arise due to freezing outdoor temperatures. If you don’t have any form of frost protection for your MVHR unit, you could experience the following issues.

  • The unit could stop working.
  • Water may appear in the ducting.
  • The unit could be overcompensating, which could lead to functional issues.
  • Less air travels through the ducting

Why can the cold affect MVHR?

Freezing temperatures can affect MVHR if the outgoing air is humid enough. If they mix, frost will form in the core of the system. MVHR systems also have draining available for any condensation that the machine collects, this can also succumb to freezing.

The core of MVHR systems will likely freeze if outdoor temperatures are below -6c. However, individual models may have exceptions to this rule, depending on their internal features.

Should I use my heating or MVHR?

You can use your central heating system in conjunction with your MVHR system, you won’t lose any heat, it is only humid air that will be extracted and replaced. MVHR systems are designed to retain heat, not generate it like a central heating system.

How can I keep my home as warm as possible?

How can I keep my home as warm as possible?

Although MVHR units help to passively maintain a comfortable temperature alongside clean air, the systems efforts may be wasted if the home isn’t already optimised to retain some level of heat. Here are some suggestions to help you retain heat in your home, with or without a MVHR unit.

  • Invest in new doors and windows if they are old.
  • Address any cracks or holes that are causing drafts.
  • Conduct maintenance on your central heating if heat distribution is unequal on the radiator, this is a sign that you may need to ‘bleed’ your radiators.
  • Apply new insulation wherever necessary.
  • Only open windows when conducting ventilation routines.

Maintaining MVHR

MVHR systems require maintenance. The amount of time elapsed between maintenance schedules will vary depending on your model. Be sure to check the guide for solid confirmation.

A maintenance routine will likely include changing the filter, and checking the status of the system and its components.

You know your MVHR system need maintenance when…

  • The system has become louder than usual.
  • There is a notable change of function.
  • There is dust in the vents.
  • There is dust on the filter.
  • Air flow intensity has altered without you attending to the system.
  • Condensation or humid environments have appeared in a room where they previously didn’t.

Do I maintain MVHR myself?

Maintaining your MVHR system yourself is possible. However, we would not recommend this if you have allergies, or no experience in maintaining a MVHR unit. We suggest getting the services of an expert.

In order to get your MVHR unit maintained by an expert, contacting a local HVAC contractor may be able to get it done for you, or at the very least tell you who to contact. The benefit of having an expert conduct a maintenance check is that they can solve any issues that may be at hand, which saves you a headache!

Purchase MVHR today

Purchase MVHR 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 answered the question ‘Do all MVHR systems require a defrost unit?’

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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