MVHR

[nod]

With thoughts are our second build 
My thoughts have turned to things I could have done the first time round 

We didn’t include MVHR Mainly due to a friend putting my wife off adding it 

While I don’t think we would ever go as far as adding solar panels 

I would like to make a case for MVHR

My wife keeps saying I went overboard with airtightness and insulation and has window and external doors open most of the time 

She suggested air con for the next build 

 

My question is will MVHR keep the house cool also 

 

[Nickfromwales]

12 minutes ago, nod said:

My question is will MVRH keep the house cool also 

In a nutshell.......no.

 

MVHR has two modes, if generic;

1) heat recovery

2) summer bypass ( so no heat recovery )

 

If you want cooling then you need an ASHP that you can reverse, and cooling batteries ( basically a fan coil ) that will allow the air to the supply valves to be sent through what is essentially a car radiator in a box which has cooled water flowing through it.

Above that, you will need air con. Depends upon if you're 3 storey or 2 story, and how you sleep at night in a slightly hotter house than you'd like.

[ProDave]

Definitely fit MVHR in a well sealed well insulated new build.

 

I assume in your present house you have trickle vents on all the windows but are still finding it a bit stuffy?

 

MVHR will ensure you have constant fresh air inside the house but without wasting heat.  It's such a simple and reliable thing there is no reason not to fit it.  Exactly what put your wife off it?

 

You can get mvhr units with a small air to air heat pump built in that will do a small amount of cooling (and heating)

[ragg987]

On a hot summer day the MVHR will reduce the heat gain. It does this by switching on the heat recovery, in effect coolth recovery. This will not work if you open all windows and doors, though.

 

You can open windows at night to cool the house then shut tight mid morning to preserve the cool.

 

1 minute ago, ProDave said:

You can get mvhr units with a small air to air heat pump built in

I understand that the air flow in the MVHR is too low to support substantial cooling, though it should work to some degree.

 

In either of the above you will get maximum benefit if you continue to pay attention to air tightness and insulation.

[nod]

15 minutes ago, ProDave said:

Definitely fit MVHR in a well sealed well insulated new build.

 

I assume in your present house you have trickle vents on all the windows but are still finding it a bit stuffy?

 

MVHR will ensure you have constant fresh air inside the house but without wasting heat.  It's such a simple and reliable thing there is no reason not to fit it.  Exactly what put your wife off it?

 

You can get mvhr units with a small air to air heat pump built in that will do a small amount of cooling (and heating)

You have just described our build 

My wife constantly says there is a lack of air 

283m2 very cheap to heat We never use the first floor rads 

UFH only needed when there is low  outdoor temps 
 

Nick answered my question 

But paused another

Will MVRH help in the summer months 

Or will it be switched off 

 

[NSS]

10 minutes ago, nod said:

 

Will MVRH help in the summer months 

Or will it be switched off 

 

 

Why would you switch it off. We run ours 24/7/365 but in summer the fanspeed is set to 1 (slowest) in the daytime and 3 (fastest other than boost) at night.

 

We do use active cooling (via UFH) when particularly warm weather for several consecutive days. That said we have SageGlass which significantly reduces the solar heat gain in the house.

[joth]

17 minutes ago, nod said:

 

Will MVRH help in the summer months 

Or will it be switched off

The MV remains on but the RH is turned off in summer:

You Still need to Mechanically Ventilate the house  year around as you still need to breathe. But no need to Recover Heat in summer as there's plenty of that.

This is what MVHR "automatic bypass" mode is for. 

[ragg987]

5 minutes ago, joth said:

The MV remains on but the RH is turned off in summer:

You Still need to Mechanically Ventilate the house  year around as you still need to breathe. But no need to Recover Heat in summer as there's plenty of that.

This is what MVHR "automatic bypass" mode is for. 

Our unit will switch on heat recovery automatically when external temp is high, I think when it gets above about 25 to 27C. This prevents the hot external air coming into the house.

[MJNewton]

25 minutes ago, ragg987 said:

Our unit will switch on heat recovery automatically when external temp is high, I think when it gets above about 25 to 27C. This prevents the hot external air coming into the house.

 

It should only do this if the external air temperature is higher than internal. So, for example, if it is 25C outside and 28C inside then it should be allowing the 'cooler' external air in (without heat recovery cell in-circuit otherwise it'll take on heat).

 

[MJNewton]

1 hour ago, nod said:

My question is will MVRH keep the house cool also 

 

As some others have mentioned, the heat recovery aspect is bidirectional - it simply transfers heat from the warmer side to the cooler. If the outside air is warmer than that inside then the heat recovery cell will cool the incoming air slightly, however looking at the graphs from my unit this tends to be only by 1 or 2 degrees (if the outside-inside differential was higher this would increase but it's an unusual scenario). Again as others have mentioned though, regardless whether it is cooling the incoming air the effect is limited by virtue of the relatively low flow rates with MVHR systems and the low heat capacity of air.

 

On a different note, we find that there is what could well be a *psychological* cooling effect with MVHR, particularly on a hot, still, night purely on the basis of knowing there is fresh air being pumped through the house and being able to feel this up close to the vents. Whether the effect is real or not arguably doesn't matter as it is only the 'feeling' of being hot/cool that matters when it comes to comfort (the extremes of heatstroke and hypothermia notwithstanding!).

 

We're fans (no pun intended) of MVHR but it's not air conditioning.

Edited July 23, 2020 by MJNewton

[Nickfromwales]

20 hours ago, nod said:

She suggested air con for the next build

Without MVHR that would just recirculate the humid stale air, ( but it would be nice and cold humid stale air at least )  

 

[nod]

As my wife says 

Why not just open a window

You won’t get much fresher than that ?

[NSS]

36 minutes ago, nod said:

As my wife says 

Why not just open a window

You won’t get much fresher than that ?

Depends how fresh (clean) the air is outside your window.

[joth]

8 hours ago, nod said:

As my wife says 

Why not just open a window

You won’t get much fresher than that ?

Well no, MVHR filters incoming air so can actually be cleaner air than opening the window.

There's many ancedental reports on here of owners needing to do much less dusting after getting MVHR. That means less dust particles floating about in the air you breathe

[joth]

Not to mention opening windows let's in smells, noise, drafts; causes doors to rattle and slam; can forget to open them in less used rooms leading damp; can forget to close them when going out or the weather changes; is bloomin freezing to do in the winter.

You can tell I'm a ventilation fan boy and we don't even have MVHR yet ? (but yesterday we did agree the delivery date for 3 weeks time, so getting close now)

Edited July 25, 2020 by joth

[MJNewton]

8 hours ago, nod said:

As my wife says 

Why not just open a window

You won’t get much fresher than that ?

 

To add to the responses above, in winter this wastes heat and on hot still summer nights can be really quite ineffective. MVHR isn't a perfect solution on either front, but the claimed efficiencies (80-90%) are actually realistic and it does keep the air moving (in a consistent and controlled way).

[nod]

57 minutes ago, joth said:

Not to mention opening windows let's in smells, noise, drafts; causes doors to rattle and slam; can forget to open them in less used rooms leading damp; can forget to close them when going out or the weather changes; is bloomin freezing to do in the winter.

You can tell I'm a ventilation fan boy and we don't even have MVHR yet ? (but yesterday we did agree the delivery date for 3 weeks time, so getting close now)

The reason we didn’t go for MVHR on the first build was a friend has it installed and doesn’t use it due to smells being staged in 

and a neighbor that Was continually Burning in the garden

He told us all this is dragged in when the MVRH is running 

So he doesn’t use it

Jerry who seems pretty clued up confirmed this at the time 

[ProDave]

Opening windows lets spiders and flies in.

 

We NEVER get any of those in winter, only in summer when some windows are opened.

[Bitpipe]

38 minutes ago, nod said:

The reason we didn’t go for MVHR on the first build was a friend has it installed and doesn’t use it due to smells being staged in 

and a neighbor that Was continually Burning in the garden

He told us all this is dragged in when the MVRH is running 

So he doesn’t use it

Jerry who seems pretty clued up confirmed this at the time 

 

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.

[Redoctober]

9 hours ago, nod said:

Why not just open a window. You won’t get much fresher than that ?

 

9 hours ago, NSS said:

Depends how fresh (clean) the air is outside your window.

 

1 hour ago, joth said:

Well no, MVHR filters incoming air so can actually be cleaner air than opening the window.

There's many ancedental reports on here of owners needing to do much less dusting after getting MVHR. That means less dust particles floating about in the air you breathe

 

1 hour ago, joth said:

Not to mention opening windows let's in smells, noise, drafts; causes doors to rattle and slam; can forget to open them in less used rooms leading damp; can forget to close them when going out or the weather changes; 

 

I'm not saying I am anti MVHR, as the system obviously has benefits above and beyond the "inconveniences" of life mentioned above. We didn't install one in our house for reasons that have been stated elsewhere within this forum but in relation to this thread I would just like to add the following for balance. 

 

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. 

 

There you go, that's my twopence worth and no, we are not having to dust everyday, empty the house of spiders/flies, have to put up with smells and prop internal doors open as a result of having windows open. Oh, nearly forgot, I don't believe the world is flat either!! ?

[Thedreamer]

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.

 

 

[MJNewton]

3 minutes ago, Thedreamer said:

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.

 

For what it's worth, ours is a 2007 Persimmon estate house* so I am sure by any measure it would unlikely satisfy this criteria yet despite this it works really well for us and I don't think we're missing out on any of the claimed benefits.

 

* Which if I didn't have first-hand experience I wouldn't touch with a bargepole but I've actually found it to be very well built. Perhaps it being the showhouse might've helped?

Edited July 25, 2020 by MJNewton

[Cpd]

2 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. 

 

@Stones has done this on Orkney and it works very well if I remember correctly, he is in a VERY exposed location ! 

[Thedreamer]

1 minute ago, Cpd said:

@Stones has done this on Orkney and it works very well if I remember correctly, he is in a VERY exposed location ! 

 

Guess if it works well in Orkney that answers the exposed location question!

[Thedreamer]

2 minutes ago, MJNewton said:

 

For what it's worth, ours is a 2007-built Persimmon estate house so I am sure by any measure it would unlikely satisfy this criteria yet despite this it works really well for us and I don't think we're missing out on any of the claimed benefits.

 

That is good for you.

 

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