We all know ventilation is important for our homes, but with so many choices and acronyms flying around it can be a bit of a minefield knowing which will be the best option for you. In this article, we are going to look at the benefits of dMVHR systems and installation placements where these units shine.
Before we begin, let’s familiarise ourselves with the different types of ventilation, where dMVHR fits in, and, most importantly, what does the acronym dMVHR stands for!
Ventilating our homes helps to remove unwanted and harmful build-up of gasses, particulates and moisture, and there are various ways to do this. The low-tech approach of opening doors and windows certainly can help, but this has the detrimental effect of also allowing heat to escape from the building, which at certain times of year is not just problematic for comfort, but financially problematic as well. Installing mechanical ventilation such as standard intermittent fans or the more effective continuous running dMEV (decentralised Mechanical Extract Ventilation) fans creates a controlled exit for these internal pollutants, managing the direction of airflow out of the building without the "open door" or perhaps "open window" policy letting the external cold air in and the internal warmth out. We do need air to be brought back into the home to replace that which is being removed but this will seep in through the fabric of the building in older houses or through trickle vents in more modern builds.
Fantastic! Problem solved! Well, for the most part, yes, but we are still losing heat through these extractor fans. Although the return of fresh air into the building won't be limited to one large volume of cold air entering through a window or door but spread across a larger area in smaller less noticeable volumes through trickle vents, air bricks and the fabric of the building to be reheated by your central heating, this air still requires heating, which in turn adds to energy bills.
The solution here is something called Heat Recovery. This style of ventilation not only extracts the stale, humid and polluted internal air but also supplies fresh filtered air back into the property. Again, not wanting to add to the heating bill, these units incorporate heat exchangers internally that glean the warmth from the outgoing air which you have already paid to heat, and pass it on to the incoming fresh air, recovering as much warmth as possible rather than venting it to atmosphere. This technique of recovering heat can reclaim up to 90% of normally lost temperature according to some manufacturer claims (Think MPG or Maximum Battery Range predictions for new cars versus real-world experience! - Ed) But as I'm sure you'll agree in the immortal words of that well-known supermarket chain, every little helps!
This technology originated in MVHR (Mechanical Ventilation with Heat Recovery) systems, which are designed to extract and supply air from multiple rooms within a home to and from one single central unit, usually housed in the loft. However, these systems which connect each serviced room to the main unit via ducting that runs through walls and ceilings are best installed during the initial construction phase or major renovation work.
Trying to retrofit MVHR into an existing home can be very disruptive unless you live in a bungalow where all the ducting runs can be installed and hidden in your loft. This is where dMVHR comes into play.
Decentralised Mechanical Ventilation with Heat Recovery (dMVHR) is essentially a heat recovery unit that both extracts and supplies air, utilising the same technology as their big brother MVHR units to reintroduce the heat to the incoming fresh air supply but for individual rooms. Wall-mounted, these units are installed similarly to standard extractor fans and are therefore a much less involved and more attractive option to existing builds.
Different manufacturers deploy different approaches, for instance, Envirovent HeatSava and Vent Axia Tempra models extract and supply simultaneously, whereas the Blauberg Vento systems deploy an alternating push/pull approach in all but one of the range, venting initially until the heat exchanger reaches a certain temperature, before switching the polarity of the fan motor to pull air back in passed the heat exchanger until the heat is spent and the process starts over!
The Vento-Duo incorporates the dual motor simultaneous approach similar to the Envirovent and Vent Axia models for their bathroom model for good reason. With the push/pull variants, having a period of in-only airflow means that not only is the steam not being removed, but by creating a level of positive pressure in the bathroom, the steam will be forced out of the bathroom and into the rest of the house, causing a wider spread of airborne moisture into the home that can spread structural damp issues - definitely not ideal.
As with all heat-exchanging ventilation, the faster the air passes the heat exchanger, the less heat it can collect. Therefore, heat recovery systems generally extract at a lower extraction rate compared to extract-only units. This can make slower heat recovery units less effective at clearing steam from bathrooms fast enough to minimise the amount of condensation that collects on surfaces in comparison with a faster-running extract-only unit such as dMEV and intermittent axial, centrifugal, and in-line fans.
Again, this is why Blauberg has produced the Vento-Duo specifically for bathrooms, as this model has a larger diameter for greater air volume to generate a higher volume of extraction while keeping the speed of the air through the heat exchanger slow enough across its greater dimensions to still effectively harvest the heat - a clever solution!
dMVHR units also generally deliver continuous-running extraction, meaning that they are always running at a low trickle speed in the background, boosting to higher extraction rates when required similar to dMEV extractor fans, which does mean that, although they may not be ideal in all bathroom installations, they do still bring the constant flow benefits in these situations. However, we would suggest extract-only options such as dMEV units for bathrooms and wetrooms that have historic or persistent damp and/or mould issues over dMVHR units.
So with this in mind, where do you install dMVHR units to gain the most benefit? Well, ventilation isn’t only required in bathrooms. Utility rooms and kitchens require ventilation in line with building regulations, and other spaces in homes can also benefit. Utility rooms often generate a higher temperature from the inclusion of white goods such as washing machines, dryers, fridges and freezers. These also generate humidity, especially from laundry, so ventilation is necessary. However, being able to save this unintentionally generated heat from being extracted not only reduces heating costs but also puts the usually regarded wasted energy of unwanted heat production from white goods to good use by introducing it to your internal heating supply!
Similarly, kitchens often generate a lot of heat through cooking and other white goods, with dMVHR systems again helping to recycle this normally lost “bonus” heat back into the house’s internal warm air circulation, again making for higher energy efficiency for your home. A standout option for kitchens is the Envirovent HeatSava range which can be mounted horizontally on a wall rather than vertically, allowing it to be placed above kitchen cabinets out of sight for a more discrete and aesthetically pleasing installation.
Other spaces can benefit, such as living spaces with open fireplaces, gas or oil fires or log burners where ventilation is important to remove the combusted and non-fully combusted gasses and particulate that these solid and fossil fuel heat sources generate. Installing dMVHR in these areas allows you to enjoy the heat source while extracting the nasty gasses etc. and introducing fresh air without losing the heat generated!
Conservatories can also benefit from dMVHR units, allowing the unit to remove the unwanted humidity build up on the glass windows while retaining the solar warmth generated by the sun passing all that glass.
It’s worth noting that dMVHR units can also benefit other living areas that struggle with damp and mould issues such as rooms with north-facing external walls or with poor natural ventilation. Understanding that combatting damp and mould has a three-sided approach is important here. Insulation, Ventilation and Heating need to be addressed together to effectively address damp and mould issues. Keeping the cold out through effective insulation, ventilating the moisture and maintaining a decent indoor temperature is made easier with dMVHR because the cost of heating and maintaining the temperature of the space is reduced if you are reclaiming the temperature from the out-going air!
Finally, bedrooms can benefit from dMVHR units by maintaining overnight temperatures but also introducing fresh air to the environment where the door is often closed for privacy overnight which reduces air movement. This makes the breathable air healthier for the inhabitants of the room by removing the build-up of carbon dioxide from respiration and also removes the moisture trapped in the room from respiration and perspiration. Most dMVHR ranges have varying models incorporating options such as humidity sensors etc. which may not be ideal for bedroom installation as automatic boosting in the middle of the night could be a nuisance for light sleepers, so either opt for a unit without these additional trigger options or for units where the boost facility can be turned off overnight for an undisturbed night’s sleep. The push/pull Blauberg Vento range is a great choice here as the units can be programmed for trickle only for a more peaceful overnight experience.
All in all, dMVHR units are a fantastic choice for homes that would benefit from heat recovery, where retrofitting a full MVHR system would be overly disruptive. Our only caveat to this is to be mindful when it comes to choosing dMVHR for bathrooms and wetrooms where a higher extraction rate is required to stop an existing damp and mould problem. For these situations stick to high-extraction units such as inline fans or constant flow dMEV units for 24 hour protection and higher boosted rates.
For more information on dMVHR systems, the link below will take you to a very good YouTube video by CharlieDIYte on the subject. He looks at a specific installation he has done initially but the second half of the video gives some good points on the benefits of dMVHR units. But again, it is a horses-for-courses approach - as with all mechanical ventilation systems, picking the right approach to ventilation by selecting the right style of system as well as taking a holistic approach to ventilation, heating and installation is key to maximising your required results.