Mechanical ventilation and heat recovery (MVHR for short) is a system that provides fresh air to all the rooms in your home. It can remove moist stale air and re-use the heat in that air to pre-heat the fresh air entering your home.
What follows is a list of the top 14 questions most commonly asked about MVHR in hopes that you will realise the benefits of such a system for your home.
So, lets jump right in.
1. How does MVHR work?
It continually changes the air in your home. It will recover any heat from that air and warm incoming air. Extract points are placed in moist areas such as kitchens, bathrooms, utility rooms and toilets. Supply rooms are bedrooms, living and dining rooms.
The heat exchanger in a MVHR will transfer up to 95% of the heat from extracted air to incoming fresh air.
2. How are they installed?
More often than not, they are installed in laundry rooms, garages or cupboards where there is easy access for maintenance. A system of ducts will be installed to extract the air from your moist areas and to supply air to your bedrooms. These ducts are connected to the MVHR unit. There will also be a control switch placed somewhere near the unit.
3. How does MVHR differ from normal ventilation?
For one you don’t need trickle vents in windows or mechanical extract fans. No background vent holes in your walls are need either. There will be draught free ventilation all year round and water vapour is removed from the air. That is great if you suffer from asthma (prevents mould growth).
4. Will it work with my heating system?
Yes. An MVHR is completely independent from the heating system. Actually, as it removes moisture from the air in your home it will improve the efficiency of your heating.
5. Can I leave my windows open?
Absolutely, MVHR systems will continue to run in background. However, the efficiency of the system will lower slightly.
6. Does the system run constantly?
Most MVHR systems will be set to run year round and you won’t have to adjust the settings. Although if you need to, you can using the control panel.
7. How much electricity will it be using?
Most MVHR systems will have 2 very small motors used to push air through the system. They run at about 22 Watts per hour. So you are looking at about 20p a day.
8. Are they noisy?
Not at all, most manufacturers develop systems that are silent.
9. Is much maintenance needed?
There is some basic maintenance you will need to do. Obviously make sure that you keep the air vents clean and clear of any obstacles. You will also need to periodically change the filter. How often you need to do this will depend on where you live and how clean the air in your home is. Generally replacements are recommended every 3 – 6 months.
10. What if my home gets too hot?
Summer purging is needed in this situation. Open your windows at nights and allow the cool air to come in. This will reduce your indoor temperature. Then during the day keep your windows closed and turn up the fan speed. This will increase ventilation and keep your home cooler.
11. Are there any health benefits?
There are quite a few actually. Most illnesses are caused or made worse by poor indoor air quality. MVHR systems remove stale moist air from your home. This reduces mould growth and dust mites. Allergy sufferers and asthmatics would really benefit.
12. How long is the pay back period?
This will ultimately depend on how airtight your house is. But you are looking at between 7 – 10 years.
13. How airtight does my house need to be?
This will get a little technical. The recommended level is 1.6 Air change per hour or 3m³/hr/m². GreenSpec have a great webpage explaining airtightness and how to improve yours. I recommend you check it out.
There you go. I hope you have found this Q+A guide helpful. Do you have any questions about MVHR systems? If so then please leave a post in the comment section and we’ll answer it.
Image: Timoleontagsheat recoverymechanical ventilation and heat recoverymvhrventilation