Has anyone researched the best dMVHR products? Planning to get one for my downstairs. I’m a bit worried about getting something and it being too noisy.
Welcome to the forum @Amy_Squire.
Generally over specified units are quieter as they will not be running outside their comfort zone. You set a restriction to your required air change rate when setting them up.
The topic has been discussed in a few threads. Have you tried searching for dMVHR, distributed MVHR or decentralised MVHR?
You could start with
I am in favour of any MVHR system, centralised or decentralised. Unfortunately, I do not have a particular single-room MVHR I can recommend. However, I have recently been looking at the new recommendations under PAS 2035. It prompted a slight change in my perspective.
Just for consideration, I quote:
“Only dMEV, cMEV, and MVHR can be used in retrofits with an airtightness of < 5 m³/m²·h @ 50 Pa under PAS 2035:2023.”
Single-room MVHRs are banned.
Logic suggests that in a very airtight home, a single-room (dMVHR) cannot guarantee the required ventilation. This is because the intake and exhaust are positioned next to each other, which can lead to contamination of the intake air.
Having said that, if you’re not solely relying on the single-room MVHR, it might be acceptable. Particularly if your home is not especially airtight. However, if it is far from airtight, then MVHR may not be very efficient and could be more costly than a standard extract system.
Which room are you intending to ventilate with it? what is your artightness, and ventilation strategy elsewhere?
Russ
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Thanks for the reply. I did have a look around yes. To be honest I can get my head around a dMVHR unit but the rest is a bit beyond me and I’m struggling to have time to learn all about it at the moment. What does an ‘over specified unit’ mean?
Thank you for the reply. Using it on an open plan floor in the downstairs of my house. At the moment very leaky but getting some air tightness work where joists meet ceiling as part of it. I still don’t think it will be extremely air tight… there’s stuff like a letter box down there and windows installed a very long time ago. I think I might just get a dMVHR unit, humidity sensor, see how it goes and be open minded about upgrading if humidity is becoming an issue. Does that seem a reasonable way forward? I just get very overwhelmed trying to understand other system and am not to sort of person who enjoys learning about it all!
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If you calculate that you need x of your preferred units of air movement and you specify x+y units then you are over specifying by y. In practice you are unlikely to find a unit that exactly matches your air change needs, so go up rather than down to overspecify. At setup you should be able to specify the trickle and boost rates.
My whole house system is a 350 m³/h one but normally runs at 235 m³/h.
Most, if not all, units have inbuilt humidity sensors. So long as the unit is on permanent trickle ventilation it will detect when the humidity rises indoors. Ideally install a sole isolated system in the most humid area to avoid drawing humid air into the rest of the house/ventilated space.
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I guess as a rough estimate just consider you want 30 m³/h (8.3 l/s) fresh air per person.
And if you can opt for a unit that ducts supply air to the other side of the room, you will actualyl get a changing of air throughout the room. (if they are available)
Otherwise you could be in danger of just recirculating the air near the unit , somewhat short circuiting the flow of air int he room. If that makes sense.
I wrote in 2021 that there are single room MVHRs with short ducts. At the time I hadn’t seen one for a while and I haven’t seen one since, so that methodology may have been abandoned. If you are multilingual it may be worth searching for what is available elsewhere.
That last comment gave me an idea and I checked Norwegian websites. There was a possible candidate, which was basically a fully ducted very small unit, designed for small open plan flats.
some of them suck out more air than they put in, so that they draw air to them from other parts of the room.
Indeed. You can get negative pressure systems, as you have, positive and balanced ones. My (whole house) MVHR has built in options for all 3 but when you can choose where to supply and extract balanced wins every time.
Beware of negative pressure systems as cold humid air could be drawn in in winter and hot air in summer.