A little bit of anti-MVHR heresy : it'll do us all good.

[Kelvin]

It’s not even like buying a car with or without aircon, in Scotland at least where MVHR is mandatory at 3 ACH. Therefore you’d need to make a decision to achieve an airtight score below the regulations but above the MVHR requirement. 
 

 

[SteamyTea]

1 hour ago, Redoctober said:

Having aircon in a car has many advantages but those who don't have it still make do

My car air con has eventually given up the ghost, after 16 years and probably 10,000 hours of usage.

[Iceverge]

2 hours ago, Redoctober said:

simple terms isn't like buying a car with or without aircon? Having aircon in a car has many advantages but those who don't have it still make do, knowing that their "lot" could be better. But on balance, they prefer to go without or do so due to budget restrictions

 

It's a bit more like buying a car without a fan and driving around with the windows open or drilling a hole in the door. 

[SteamyTea]

Just now, Iceverge said:

drilling a hole in the door.

Well letting the grease monkey drill the hole, but not tell you where, or how large it is.

[ToughButterCup]

3 hours ago, Dave Jones said:

...To me a well insulated, airtight house without MVHR should not be issued with a completion cert as its not fit for use.

 

Exactly correct. And ours will have an MVHR system.  But not for a while yet.

The issue is that I -  incorrectly, naively, stupidly - thought that the house wouldn't be habitable without MVHR. Thats wrong.

6 months of the year, we have one or more windows open all the time.  So its a bit like our towel radiators - off for 6 months a year

[SteamyTea]

9 minutes ago, ToughButterCup said:

The issue is that I -  incorrectly, naively, stupidly - thought that the house wouldn't be habitable without MVHR. Thats wrong.

For hundreds of year people thought you did not need a flushing bog in the house.

Some people still think that antibiotics and vaccines are unnecessary, but happy to take pills their friends give them.

[Mike]

I remember trying to convince people that double glazing was worthwhile.

[George]

It'd be better if the MVHR system responded to sensors like CO2 and humidity and was otherwise powered down. In my rennovation with more smaller rooms, I think the trickle MVHR does play an important role in pushing air out into the more ventilated communal areas, which may be less of an issue than with a complete new build design.

 

When asked I do recommend people look at single room MVHR systems rather than trying to force a whole house system in (as I did). I managed it but it was literally and figeratively painful.

[Iceverge]

On 29/08/2023 at 13:36, George said:

It'd be better if the MVHR system responded to sensors like CO2 and humidity and was otherwise powered down

 

They do exist,I think Aldes do one. 

 

Most of us just tweek with the flow settings post install to achieve an air change rate that the troughs of low demand balance out with the highs of the peak demand and let the volume of air in the house buffer the changes. 

 

In practice it works fine although the CO2, RH and VOC levels will vary throughout the day. If you can live with this varying but still acceptable air quality the cost and complexity of a constantly adjusting system may not be worth paying for. 

[Jim K]

I also want to minimise the MVHR running when there's less of a reason for it to be on --  e.g. windows/doors open, smells or bonfires outside. And, when humidity is low or we're out, I want the system to spin down to low or turn off for a while.

 

So, I have a 4 channel wifi controller attached to my Vent Axia Sentinel Kinetic BH that allows me to use Home Assistant (and Google) to switch from auto to any of low, normal, boost of turn it off, and back. I plan to add some automatons that use temp/humidity data from the Tado radiator valves, door and window sensors and weather forecast to override the auto-boosting humidity sensor when it's appropriate. The goal is to maximise comfort and minimise power usage, plus generally allow anyone at home to say "hey google, turn off the ventilation" when the local farmer inevitably spreads a bunch more poop on the fields, as he does at least once a month. In my retrofit bungalow I don't have to be super-concerned about a few hours or even a day without the system running as it's draft free but not ultra-airtight.

Edited August 31, 2023 by Jim K

[joe90]

I presented a discussion re turning MVHR off when not needed here a long time ago, if I remember correctly CO2 sensors are either very expensive or inaccurate but was told CO2 is closely linked to humidity so a simple humidity sensor could switch the MVHR off if not required (I fitted a humidity sensor to control boost after bath/shower/cooking.)

[SteamyTea]

2 minutes ago, joe90 said:

was told CO2 is closely linked to humidity

That came from my analysis of @DamonHD's data from a class room (literally just finished reading one of his dad's books).

It was pretty detailed as it took weather and traffic into consideration.

 

There is a lot of false facts about CO₂ and the affects it has on people. We can tolerate what seems quite high levels with no ill affects and often no noticeable affects.

So, in my opinion, RH is perfectly good for ventilation control.

It would be useful to add a couple of particulate sensors, then you could reduce infiltration rates when they are high outside, or purge the building when high inside.

 

[MikeGrahamT21]

@ToughButterCup have you ever lived in a property which has MVHR? No one else I know has anything like I do, and their houses are stuffy to me, but you don’t realise until you’ve had MVHR.

 

maybe you open windows/doors more than you would if you had it, I don’t open much up year round, unless I’m out in the garden.

 

And if you’ve ever seen a used MVHR filter, surely you don’t want all that crap over carpets, furniture and in your lungs?

 

for me MVHR chips away at humidity like nothing else I’ve ever experienced, and the house smells fresh all year round, I deal with exterior smells with a carbon filter which works brilliantly. And the unit itself, cost me £400 off eBay brand new, plus another £150 for the upgrade to Hepa filters and carbon, the pipes you already have in place so maybe just keep an eye out?

 

honestly can’t think you’ll ever regret it, just fit and forget for the sake of around 40W of power or less

[joe90]

4 minutes ago, MikeGrahamT21 said:

And the unit itself, cost me £400 off eBay brand new,

Mine was even less on EBay.

[Jim K]

So, to summarise this thread (and much of this MVHR forum area tbh):

• MVHR is a great enhancement to many homes that are reasonably well sealed -- the benefits can be great even for less airtight properties due to fresh air and significant humidity reduction, with all the associated benefits of those.
• There are rooms in many houses that don't have enough ventilation, or even any windows. So opening doors and windows aren't necessarily a solution, especially in winter.
• Don't buy expensive units and ducts unless you're chasing that last few watts here and there for very high performing properties. For retrofit, cheaper units and eBay are your friend.
• Use it how you want -- turn it off, up, or down whenever you feel like. But Passivhaus properties are designed around it so expect some consequences.
• Use windows and doors as you see fit - you have the flexibility. But probably don't turn the unit off with all the windows shut for extended duration.
• Make it smart if you can, or just ignore it and let it do its thing. Humidity is cheap and easy to measure and a good proxy for CO2 and other air quality issues.

Right?

[JohnMo]

20 minutes ago, Jim K said:

Don't buy expensive units and ducts unless you're chasing that last few watts here and there for very high performing properties. For retrofit, cheaper units and eBay are your friend.

I would temper that with, a remark on noise and overall reliability.  Also support and spares if things aren't quite right. I bought my units from eBay but expensive units for super cheap prices. One unit had an issue, got great support from Titon and had the spares in two days.

 

Set it up per building regs then once signed off, used the setback setting, which knocks fan speed down to between min speed and current speed setting. Rarely use boost, totally silent, zero drafts, monitor CO2 in master bedroom and lounge - zero issues. Runs 24/7, nothing smart, manual boost switches. Complex controls if you like, but no need.

[ToughButterCup]

Rare to see a thread where readers make the effort to summarise accurately.... Thanks very much.

 

I made the error of thinking MVHR would have to be ON all year round. Here - as opposed to many other places - we won't need it to be ON for a few months a year. 

 

But we do need it. 

 

Next problems: Which unit? How much?

[JohnMo]

I have two units, but that's to do with our house layout and the resulting duct lengths. My whole system was under £2k installed. I like Titon HRV, UK made, good tech support and spares on the shelf. Often come up on eBay for super cheap prices.

[Jim K]

I've gone with the mid range Vent Axia Sentinel Kinetic. Only £899 in the Air Shop sale and good support, parts and usage across the UK and Europe. Those fancy units aren't worth it for my retrofit - and most will not go through my loft hatch. Everything should be about £2k all in, including core drill bits etc.

 

I'll be installing mine starting as soon as the ducting arrives from BCP, ideally will have it in by end of September.

 

Another bunch of hours in the loft, yay... I hate it up there 😅

Edited September 2, 2023 by Jim K

[MikeSharp01]

On 01/09/2023 at 08:31, JohnMo said:

. I like Titon HRV, UK made, good tech support and spares on the shelf. Olljften come up on eBay for super cheap prices.

Yes we are going Titon - the new HRV4 I am hoping.

[JohnMo]

1 hour ago, MikeSharp01 said:

Yes we are going Titon - the new HRV4 I am hoping.

Have a look at Beam also, they are the same units rebranded (much lower price when I last looked) and the accessories are the exact same.

[dpmiller]

Do Beam sell onto the mainland?

[JohnMo]

I have bought bits from them

[eandg]

On 23/08/2023 at 16:00, Kelvin said:

It’s not even like buying a car with or without aircon, in Scotland at least where MVHR is mandatory at 3 ACH. Therefore you’d need to make a decision to achieve an airtight score below the regulations but above the MVHR requirement. 
 

 

Which is where? Asking for our summer house which I'm planning - I don't think I can take my sustainable head off but at the same time I don't want to have to put MVHR in the space (and pay for it). 

[JohnMo]

9 hours ago, eandg said:

Which is where? Asking for our summer house which I'm planning - I don't think I can take my sustainable head off but at the same time I don't want to have to put MVHR in the space (and pay for it). 

Our summer house is almost air tight, until it came to the windows supplied, they are a leaky pile of x"xx.

 

But I decided a dMEV fan was good enough. Part time use building, set it to min flow rate, which means it silent. Also in a small well insulated building, any noise from fans is ever present, so care is needed