MVHR

[MJNewton]

  

33 minutes ago, Thedreamer said:

 

I think there maybe some luck when it comes to developer houses. Prehaps I've read to many Daily Mail articles. 

 

Yes, I think you're probably right (Edit: With the luck bit, not reading too many DM articles... Edit 2: Although on second thoughts! ). 

Edited July 25, 2020 by MJNewton

[Bitpipe]

51 minutes ago, Thedreamer said:

Another here that didn't put it.

 

I think location is important. I am not sure I would put say if I had neighbours close by with stoves and my plot was in a valley.

 

I don't get this - you still need to ventilate your house - air needs to come in from outside irrespective of the means - smells and all.

 

If one of my neighbours has a smokey bonfire, I turn off the MVHR for a few hours - same as I would have closed windows in the past.

 

51 minutes ago, Thedreamer said:

I would be interest ed to hear from those that have installed it how it performs in a exposed locations with 60pmh winds. 

 

I would only install it if I was responsible for the air tightness. If you buy a house from a developer that has not had an individual airtest close to completion it may be a complete waste of money. For hands on self builds or if using good trades it make good sense to install it.

 

A friend has an 80's developer box and built a sizeable 2 story extension, added MVHR and says it has made an improvement to air quality and humidity (bathrooms & showers) but appreciates that the heat recovery element is probably not doing anything due to poor airtightness on the original fabric.

 

2 hours ago, Redoctober said:

Prior to installing a system, you have to weigh up the capital investment against any benefits. Then there is the ongoing maintenance and replacement of filters. Also you have to ask yourself whether or not you can live with having the inlet / outlets ducts being constantly visible. 

 

This is a sensible approach - however you'll still need external vents for your kitchen and bathroom mechanical extraction to meet Regs so you can't completely eliminate them. I've also seen MVHR vents built into the roof so pretty much invisible.

 

My system cost about £3800 all together (ExVAT) and I self installed - probably larger than most due to basement, 20 ceiling valves in total and 350m of internal duct. So not cheap but I do not see how I would have efficiently and effectively ventilated our house by traditional means without.

 

[Stones]

3 hours ago, Bitpipe said:

 

The problem there was your neighbour, not your MVHR.

 

Suggested Rationale:

 

External air needs to enter the house somehow (MVHR, upon doors / windows trickle vents, leaks) and stale (usually damp) air needs to exit the house somehow (extractors). If not, you will suffocate and the house will be damp and smelly. B Regs also insist on this and you need to satisfy them, so you need to choose something.

 

Now that the 'need to ventilate' principal is established, you can decide if you want an efficient system that, when you want to, will preserve the internal heat you've paid for or just flush it our and you pay again to replenish it.

 

You can also decide if you want to filter the air that comes into your house or let all the dust, pollen and other stuff come in with it. I'll send you a pic of my next filter change and you can see what didn't make it into the house.

 

Now, whether you keep every door and window closed year round is up to you. During the summer months, we tend to have the living room slider cracked open as the cat likes to come and go, as do the kids, plus the atrium Velux windows and the wife occasionally will open the bedroom balcony door at night if she's feeling warm.

 

If it's particularly hot out, we'll 'cold purge' ventilate at night and try to keep closed during day to keep cold air in, winter obvs we're sealed up.

 

MVHR also helps clothes dry quicker inside.

 

MVHR is NOT very efficient at drastically raising or lowering room temperature as the airflows are, by design, low and air is a poor conductor of heat. They can be used as a 'trim' but if you want central air  cooling then you need to use a separate system that has much higher air flows. However the MVHR will play its part as it will help keep that nice cold air you paid for in the house vs have it escape out trickle vents etc.

 

A very good summary of the benefits and how we use our system.  I would add no condensation on windows etc in the house.  

 

1 hour ago, Thedreamer said:

Another here that didn't put it.

 

I think location is important. I am not sure I would put say if I had neighbours close by with stoves and my plot was in a valley.

 

I would be interest ed to hear from those that have installed it how it performs in a exposed locations with 60pmh winds. 

 

I would only install it if I was responsible for the air tightness. If you buy a house from a developer that has not had an individual airtest close to completion it may be a complete waste of money. For hands on self builds or if using good trades it make good sense to install it.

 

 

 

As @Cpd says, we have MVHR here, without much if any shelter and winter wind speeds of 60mph plus in winter. Genuinely, not an issue, it just works away.  I fitted the inlet and exhaust vents on the leeward side of the house.  Occasionally you do hear the fans struggle when the wind gusts at extreme / is swirling multi direction, due I think to pressure differentials. Having rented a 15 year old house here while we built, that slight occasional imbalance was far better than the whistling and howling gales that would come through extractor fans and trickle vents!

 

We have had MVHR in 5 houses now, the first back in 2003 when airtightness and good levels of insulation weren't really a consideration! The difference even then to the house before which had trickle vents and extractor fans was night and day and it's something I wouldn't go back to by choice. 

 

[joe90]

Another here that installed MVHR but I must admit we are “open window” people so frankly during the summer I switch it off. I always said I thought it would be better controlled by a “poor air quality stat” but they don’t exist!!! (Threads on this subject have existed in the past).

[Thedreamer]

1 hour ago, Bitpipe said:

 

I don't get this - you still need to ventilate your house - air needs to come in from outside irrespective of the means - smells and all.

 

If one of my neighbours has a smokey bonfire, I turn off the MVHR for a few hours - same as I would have closed windows in the past.

 

My point was if you live somewhere where smokes settles you might not be able to use MVHR much in the winter.

 

Plenty of small glens here I pass one on the way to work that has been gutted and MVHR fitted and next door an old croft house burns coal, wood and peat through the year the smoke often lingers in the air and I can only presume that it is pulled into the system.

 

Would filters work effectively in this situation?

 

Would their be a difference between the air sucked in via mechanical means rather than through the fabric of the building?

 

My point is that location might be a consideration.

 

Quote

 

A friend has an 80's developer box and built a sizeable 2 story extension, added MVHR and says it has made an improvement to air quality and humidity (bathrooms & showers) but appreciates that the heat recovery element is probably not doing anything due to poor airtightness on the original fabric.

 

 

 

Why would you fit MVHR in that situation? Vent the air via extraction fans and fresh air then through the trickle vents.

[Bitpipe]

35 minutes ago, Thedreamer said:

 

My point was if you live somewhere where smokes settles you might not be able to use MVHR much in the winter.

 

Plenty of small glens here I pass one on the way to work that has been gutted and MVHR fitted and next door an old croft house burns coal, wood and peat through the year the smoke often lingers in the air and I can only presume that it is pulled into the system.

 

Would filters work effectively in this situation?

 

Would their be a difference between the air sucked in via mechanical means rather than through the fabric of the building?

 

MVHR filters, especially F1 can certainly remove pollen, not sure if smoke particulate would be too small.

 

But the external air is the external air, if it's smokey then it's coming into the house one way or the other.

 

In a non MVHR house, what do you think happens when you run the bathroom or kitchen extractor for 20 mins? The fan will cause external air to enter the house via trickle vents and general building fabric, gaps around doors etc. smoke and all.

 

 

Why would you fit MVHR in that situation? Vent the air via extraction fans and fresh air then through the trickle vents.

 

Extraction fans usually only come on when you've just used the bathroom (15/30 min timer) or cooking in kitchen.

 

He finds that a continuous low level of filtered air coming to every room has improved the air quality and reduced humidity, especially in bathrooms.

 

He's aware that the efficiency, especially heat recovery, will be much lower than a new build but says that it makes a noticeable air quality difference - especially in winter.

[joth]

9 hours ago, joth said:

Not to mention opening windows let's in smells,

Good lord sorry all for mentioning this. The specific case I was thinking of (not so unlike our own) was a house near a busy smelly road can get all their fresh air from the furthest point from the road with MVHR, rather than have to open windows right onto that noisy smelly road. 

As many point out it's no where near as clear cut as that in the general case, where sometimes MVHR could be unlucky and fair much worse than an open window, but in average as @Bitpipe has eloquently described in the face of pervasive smells it's likely no difference either way, so I'll gracefully retract this specific claim if I may? ?

 

[Thedreamer]

3 hours ago, Bitpipe said:

 

MVHR filters, especially F1 can certainly remove pollen, not sure if smoke particulate would be too small.

 

But the external air is the external air, if it's smokey then it's coming into the house one way or the other.

 

In a non MVHR house, what do you think happens when you run the bathroom or kitchen extractor for 20 mins? The fan will cause external air to enter the house via trickle vents and general building fabric, gaps around doors etc. smoke and all.

 

 

Extraction fans usually only come on when you've just used the bathroom (15/30 min timer) or cooking in kitchen.

 

He finds that a continuous low level of filtered air coming to every room has improved the air quality and reduced humidity, especially in bathrooms.

 

He's aware that the efficiency, especially heat recovery, will be much lower than a new build but says that it makes a noticeable air quality difference - especially in winter.

 

That all makes sense.

[joe90]

24 minutes ago, joth said:

Good lord sorry all for mentioning this. The specific case I was thinking of (not so unlike our own) was a house near a busy smelly road can get all their fresh air from the furthest point from the road with MVHR, rather than have to open windows right onto that noisy smelly road. 

As many point out it's no where near as clear cut as that in the general case, where sometimes MVHR could be unlucky and fair much worse than an open window, but in average as @Bitpipe has eloquently described in the face of pervasive smells it's likely no difference either way, so I'll gracefully retract this specific claim if I may? ?

 

No, Jeremy mentioned a problem with a neighbours bonfire causing smoke/smell in his house with his MVHR, he just turned it off fir a while. WIth regard a noisy smelly road, yes another plus for MVHR.

[Bitpipe]

1 hour ago, joe90 said:

No, Jeremy mentioned a problem with a neighbours bonfire causing smoke/smell in his house with his MVHR, he just turned it off fir a while. WIth regard a noisy smelly road, yes another plus for MVHR.

 

A nice feature would be if the MVHR could detect smokey air on the intake and temporarily shut down (bit like the humidity sensor on the extract triggering the boost feature).

 

I'm sure someone handy on here could suggest how you could re-purpose the detector on a smoke alarm to do this....

[Onoff]

21 minutes ago, Bitpipe said:

 

A nice feature would be if the MVHR could detect smokey air on the intake and temporarily shut down (bit like the humidity sensor on the extract triggering the boost feature).

 

I'm sure someone handy on here could suggest how you could re-purpose the detector on a smoke alarm to do this....

 

Just pick a detector with a relay output (like an Aico with optional module) and disable the inbuilt sounder. (Don't interconnect the alarm either). Use the relay to switch off the MVHR and a warning light on maybe. 

 

https://www.aico.co.uk/product/ei128r-hard-wired-relay-module/

 

Edited July 25, 2020 by Onoff

[PeterW]

1 hour ago, Bitpipe said:

 

A nice feature would be if the MVHR could detect smokey air on the intake and temporarily shut down (bit like the humidity sensor on the extract triggering the boost feature).

 

I'm sure someone handy on here could suggest how you could re-purpose the detector on a smoke alarm to do this....

The problem is one of airflow. If you stop the airflow when smoke is detected, you then need to pulse the intake fans regularly to see if the smoke has stopped otherwise you won’t have an airflow to test for smoke... 

[Bitpipe]

11 hours ago, PeterW said:

The problem is one of airflow. If you stop the airflow when smoke is detected, you then need to pulse the intake fans regularly to see if the smoke has stopped otherwise you won’t have an airflow to test for smoke... 

 

This is why you look after the clever technical bits of BuildHub and I do the occasional backup

 

[MJNewton]

11 hours ago, PeterW said:

The problem is one of airflow. If you stop the airflow when smoke is detected, you then need to pulse the intake fans regularly to see if the smoke has stopped otherwise you won’t have an airflow to test for smoke... 

 

An easy way to do this could be to feed the alarm relay output into something like a Shelly 1 smart relay (~£10) and set its 'Auto On' timer to, say, 30mins. After the trigger signal is received from the smoke alarm  it'd power down the MVHR and restart it after 30mins - if the smoke still persists the cycle will be repeated. It'd allow manual override (on or off) via your phone too if desired. 

Edited July 26, 2020 by MJNewton