Like most things, we wish there was a simple answer to this. But the truth remains: it very much depends on many factors. Really, it all comes down to what you want to achieve, what you want to spend, and how effective you want your ventilation to be.

But how do they compare against each other? And which one is the right solution for your home, installation, or stock range?

 

Intermittent Extract Fans – The Traditional Choice

An Intermittent Extract Fan is the standard on/off fan that most people are familiar with- typically installed in bathrooms and kitchens. They’re usually activated by a light switch or a humidity sensor to extract stale, moisture-laden air when needed and usually turns off after a set period of approximately 15-20 minutes.

Intermittent extract fans are a simple solution for ventilating wet rooms. Whilst they are inexpensive and easy to install, they don’t offer the same continuous protection against damp, high humidity and poor air quality as other solutions.

So, let’s look at the pros and cons of this solution…

✅ Low cost & easy installation- One of the most affordable ventilation solutions for homes, with straightforward installation and minimal ductwork.

✅ Low energy use- Intermittent fans only run when they are triggered and therefore don’t use continuous energy like other ventilation options.

✅ Easy to replace or upgrade- If something goes wrong with an intermittent extract fan, swapping it for a replacement is very quick and easy to do.

❌ The environment is not consistently controlled- Since they are only activated when purposely switched on or triggered, the fan won’t provide constant control for moisture, humidity or odours. Over time, this can allow condensation to build up and cause damp conditions which can lead to mould problems. This obviously is not good for the health of the occupants or fabric of the building.

❌ Noise levels- The majority of extract fans on the market are noticeably louder which can be disruptive around the home.

❌ Less effective in airtight homes- As homes become more and more airtight, the intermittent approach (if not done right) can very quickly not meet desired standards. The airtight nature of the building and intermittent operation can allow humidity levels to rise, causing increased condensation, damp and poor IAQ. This is why people are more frequently looking at a continuous strategy.

 

dMEV – Decentralised Mechanical Extract Ventilation

dMEVS are becoming increasingly more popular as an alternative to intermittent extract fans, providing low level continuous extraction in areas such as bathrooms, kitchens and utility rooms.

Located in the ceiling or straight through the wall, they run 24/7 at a low speed to continuously remove stale air and ramp up when humidity levels rise, and faster extraction is needed.

The pros and cons…

✅ Better moisture control- Unlike intermittent fans, dMEV products provide a steady removal of moisture and pollutants. This constant approach reduces the risk of damp and mould issues as a result of high humidity levels.

✅ Quiet operation- As these fans run at a consistent low speed, they are usually significantly quieter than the traditional intermittent extract fans.

✅ Energy efficient- Most dMEV units (including our own!) use EC motors and are very energy efficient even though they are continuously running.

❌ Higher initial cost- In comparison to an intermittent extract fan, dMEV units are generally a little more expensive to buy.

❌ Ongoing energy use- Although dMEV fans are extremely efficient, they are still constantly running which will use a small amount of energy per year. We have a running cost calculator available to use on our website to give you a rough idea of the running costs of not only our fans, but anyone else’s too. You might be surprised though as they are not as expensive to run as you might think!

 

MEV – Centralised Mechanical Extract Ventilation

Now let’s talk about MEV systems… The centralised approach to continuous extract ventilation.

Unlike dMEV units which are installed in individual rooms, MEV systems use a central fan unit connected to multiple rooms via a network of ducting. This setup provides whole-house extraction from wet rooms using one single, continuously running unit which is typically located in a loft space or first floor cupboard.

This makes it a great solution for new builds or refurbishments where ducting can be neatly incorporated.

✅  Whole-house coverage- One central fan can ventilate multiple rooms at once, improving indoor air quality across the entire home.

✅  One fan unit- A single point of control to make life nice and simple.

✅  Aesthetics- You only see a ceiling valve/register, so if you are not a fan of seeing individual fan units on the wall and ceiling in each room, this is a great option for you!

✅  One break out point- You only need one external penetration through your roof or wall as opposed to individual break out points, like you get with dMEV. This reduces the amount of work required to install the fan unit and is much more aesthetically pleasing.

✅   Quiet & efficient- Positioned away from living spaces, MEV units are typically very quiet in operation, and EC motor options make them energy-efficient.

❌   Complex installation- An MEV unit requires planning for ducting and space for the central unit, which can be challenging in retrofit scenarios.

❌   Higher upfront cost- Equipment and installation can be more expensive compared to simpler systems.

 

PIV – Positive Input Ventilation

Very simply, PIV systems work by drawing air in, typically from the loft, and filtering it to remove pollutants and allergens, and then gently introducing this fresher air to the first-floor landing. This creates a positive pressure environment, which pushes stale, moist air and other indoor pollutants, such as mould spores, dust mites and volatile organic compounds (VOCs), out through natural leakage points within the building.

This continuous process of introducing fresher air and expelling stale air not only improves air quality but also helps to maintain a healthy indoor environment, reducing the risk of respiratory problems and other health issues associated with poor indoor air quality.

✅ Great for tackling condensation – Constant airflow reduces the risk of damp and mould.

✅ Improves indoor air quality – New filtered air displaces pollutants, allergens, and odours throughout the property.

✅ Easy to install and low maintenance – Less intrusive to install with minimal ductwork and a single point of air supply. A simple filter change for maintenance is all it takes!

✅ Cost effective solution – Lower capital cost than other solutions and lower cost to install.

❌ Background ventilation needed – PIV units rely on natural leakage points or trickle vents in order to work effectively. This means it is not suitable in homes that have been built too airtight.

❌ Unless the PIV is connected to a heater, it can potentially feel like a cold air is being introduced. The dilemma here is the trade-off between slightly warmer incoming air and the cost to run the electric heater. Theres no right or wrong it just depends on your comfort levels and preference.

❌ Relies on a suitably ventilated loft space – Without enough free air, PIV might not be the best option and whilst you can duct to atmosphere you need to be careful with ducting and ambient temperatures.

 

Alternate Flow Single Room Heat Recovery Units

Single Room Heat Recovery units are a form of decentralised ventilation. The systems consist of individual fans installed in specific rooms (normally bedrooms or living spaces), providing targeted ventilation and a boost to air quality where it’s needed most.

These units help a room “breathe” and reduce indoor air pollutants and humidity levels. Designed for individual rooms, these compact fans alternate (every 70 seconds) between supply and extract modes, enabling a constant cycle of fresh air while recovering heat from the outgoing air. Additionally, they have filters too, which helps clean the incoming air!

✅ Heat recovery without ductwork – Perfect for retrofits or rooms where whole house MVHR installation isn’t possible.

✅ Quiet & efficient – Ultra-low noise levels and high thermal efficiency make them great for bedrooms or living areas.

✅ Simple to install – Typically fitted through an external wall and controlled via a simple panel or remote.

✅ Cost effective – Same benefits as a whole house MVHR, but without the costs.

❌ Only suitable for individual rooms- Doesn’t offer whole-home ventilation.

❌ May not be the most aesthetic option – If you have multiple units in a property then this means lots of holes in the walls and lots of external louvre grilles.

❌ Hidden installation costs – Whilst not the most expensive solution to install, you need to consider the installation costs, and particularly the electrical works involved.

MVHR – Mechanical Ventilation with Heat Recovery

MVHR systems continuously extract stale, moist, humid air from wet rooms and simultaneously supply filtered air to living areas. They also use a heat exchanger to transfer warmth from the outgoing air to the incoming air without mixing them, improving indoor air quality and reducing energy loss. This approach helps to maintain a consistent, comfortable indoor environment and supports energy efficiency. Essentially, it is an all-in-one solution for the best indoor air quality possible.

All ventilation specialists love an MVHR, however, they aren’t always the easiest to install as they require ducting throughout the home.

✅ Whole-house solution – Ideal for airtight homes and new builds with quiet operation.

✅ Energy efficient and energy saving – Recovers up to 90% of the heat from extracted air.

✅ Consistent indoor air quality – Increased comfort levels for occupants and also great for allergy sufferers and improving general health and wellbeing.

✅ Effective and reliable solution – Very effective solution to ensure no condensation, mould, or stale air. Also does not need to rely on trickle vents or open windows.

✅ Low running costs – Inexpensive to run once fitted.

❌ Higher initial cost – The initial investment and installation costs for an MVHR are generally higher than other systems.

❌ Requires ducting – To install an MVHR system, ducting is required to be installed throughout the house. This means that this solution is usually best suited to new builds or extensive renovations where ductwork can be installed during the build.

❌ Early consideration is required – If MVHR is the solution for you then this needs to be planned and considered early so you can factor in all the required ducting and MVHR unit location. The earlier the better!

 

So, which one should you choose?

When it comes down to Intermittent vs Continuous (dMEV or MEV), we would usually recommend a continuous strategy because of the benefits a continuous running strategy provides. Whichever one you choose though, one thing not to forget is with a extract only strategy, all need sufficient background ventilation typically achieved through window trickle vents or air transfer grilles.

There are a number of considerations when looking at the best option for your home or your customers, the truth is that a continuous fan will ultimately provide better indoor quality overall. Although the initial upfront cost is more and running costs a little higher, it is always better to prevent condensation, damp and mould within a home rather than having to fix it when it’s too late.

At the end of the day, all ventilation options have their pros and cons. If you’re looking to ventilate one room efficiently with minimal disruption, a dMEV unit is going to be a good option. Whereas if you’re building or renovating a modern, airtight home, MVHR is probably going to be your most effective long-term solution.

Remember, a good solution for one property doesn’t mean it’s right for another. It all comes down to your property type, budget, and performance goals.