MVHR installers or alternatives?

[Roger440]

On 02/01/2026 at 21:34, Iceverge said:

I think Aereco had the original design. 

 

As I understood it it's just a strip of nylon that expands and contracts with humidity. 

 

20Pa really isn't that much. 100000Pa is 1 Bar or about 14psi.

 

Thanks. All the blurb i can fins suggests there needs to be a fan somewhere, you a PIV for them to work. 

 

But it seems they are a mystery product, theres just no info beyond the basic website description.

 

Im attracted to the concept as, essentially theres nothing to go wrong, and doesnt use any power. Which seems too good to be true. And we all know what that normally means!

[JohnMo]

12 hours ago, Roger440 said:

Its far from clear how these work. Google not much help either. What causes the air to move when they are open, as it says you need 20ps air pressure difference

There effectively a piece of string, but the string expands and contracts with changes in humidity - it senses room humidity it changes length as the humidity increases to open the vent more. 

 

You to have them coupled with MEV or dMEV fans in wet rooms. If these boost automatically, you get a system that self compensates for changes in room habitation etc.

 

So example everyone in lounge in evening, vents in lounge window open, but rest of house vents go to min position, fans draw air through house taking most air from lounge. Everyone goes to bed, lounge vents close and bedroom vents start to open etc 

[Roger440]

27 minutes ago, JohnMo said:

There effectively a piece of string, but the string expands and contracts with changes in humidity - it senses room humidity it changes length as the humidity increases to open the vent more. 

 

You to have them coupled with MEV or dMEV fans in wet rooms. If these boost automatically, you get a system that self compensates for changes in room habitation etc.

 

So example everyone in lounge in evening, vents in lounge window open, but rest of house vents go to min position, fans draw air through house taking most air from lounge. Everyone goes to bed, lounge vents close and bedroom vents start to open etc 

 

Thanks. That makes sense. So, as i suspected there still needs to be a mechanical fan somewhere.

 

Interesting though. 

 

Until i see where i get to with air tightness, cant really make any decisions.

[JohnMo]

8 minutes ago, Roger440 said:

 

Until i see where i get to with air tightness, cant really make any decisions.

In Scotland air tightness better than 3.0, balance inlet outlet ventilation mandatory, so MVHR. 3 to 5 MEV or dMEV (with trickle vents), after that whatever fancy passive vent intermittent fans etc, all with trickle vents.

[mickeych]

12 hours ago, G and J said:

Do you use the fancoils much?

Not really. We leave them on auto so if the temperatures drop in the upstairs bedrooms they cut in which is very rare.

We had some teething issues in the summer getting them to work effectively, but once they were properly sealed into the ductwork they worked a treat reducing the temperature in the bedrooms to 18 from 28 very easily. They are currently set to run at a fairly low speed to not be intrusive and have not needed to boost them so they are doing what we designed them to do.

[saveasteading]

24 minutes ago, mickeych said:

reducing the temperature in the bedrooms to 18 from 28 very easily

Windows do that.

 

[mickeych]

On 03/01/2026 at 11:11, saveasteading said:

Windows do that.

 

No they don't when the outside temperature is 28 😉

Edited Sunday at 17:31 by mickeych

[G and J]

On 03/01/2026 at 10:46, mickeych said:

Not really. We leave them on auto so if the temperatures drop in the upstairs bedrooms they cut in which is very rare.

We had some teething issues in the summer getting them to work effectively, but once they were properly sealed into the ductwork they worked a treat reducing the temperature in the bedrooms to 18 from 28 very easily. They are currently set to run at a fairly low speed to not be intrusive and have not needed to boost them so they are doing what we designed them to do.

Forgive the interrogation but…

 

Are your fancoils on their own zone or together with your UFH?   I ask as we are installing our main bedroom fancoil as part of the single zone, but with the ability to zone it off later if needed. 

[Mike]

On 01/01/2026 at 12:23, Eastfield said:

It's all very well those with MVHR stating they'd never live in a house without it, but have they lived in modern, well insulated home with well designed ventilation but no mvhr by comparison? I'd be keen to hear from anyone who has in order to gain an unbiased view.

One of the first attempts to do that in the UK was the Beddington Zero Energy Development, better known as BedZED, completed in 2002. I must have visited it in 2003. It used passive stack ventilation, aided by wind-driven roof fans, with plate heat exchangers for passive heat recovery - nothing electro-mechanical. Airtightness 2.5 ACH at 50 Pa. 300mm wall floor & roof insulation. 133 kWh/m² to 331 kWh/m².

 

As this was a very high-profile pioneering development follow-up surveys were carried out. There's probably a better source but I've tracked down a thesis that includes some of the results here: Lessons Learned from the BedZed Development, J Young.

 

TLDR: Almost half of the survey respondents did not think the ventilation system at BedZED was effective at removing moisture and smells. Condensation or mould was reported by 6 out of 18 residents surveyed (though 1 had bunged up their air intake to stop cigarette smoke entering).

 

Edited 20 hours ago by Mike

[JohnMo]

On 04/01/2026 at 22:24, G and J said:

Are your fancoils on their own zone or together with your UFH?   I ask as we are installing our main bedroom fancoil as part of the single zone, but with the ability to zone it off later if needed. 

You don't really need to zone a fan coil, as you can program the fan coil, it will just modulate or switch off the fan as needed. If you add a zone valve, you start to drive your way towards a buffer. Better to leave the fan coil in circulation system all the time.

[Nickfromwales]

9 minutes ago, JohnMo said:

You don't really need to zone a fan coil, as you can program the fan coil, it will just modulate or switch off the fan as needed. If you add a zone valve, you start to drive your way towards a buffer. Better to leave the fan coil in circulation system all the time.

If it’s in an isolated space, or on another floor, then it is advantageous if it can run on longer, or fire up sooner, but I wonder then if you’d defo need a decent sized volumiser to allow that to run independently.

 

Heating or cooling would need to be ‘on’ for the main heating system, for a fan coil to toggle in / out, so I guess it’s down to how the system is run and configured.