Idiots guide to mvhr.

[Russell griffiths]

I’m getting to the point when I need to start looking at all the stuff to go inside the house, yes I know I should have done this a year ago. 

Anyway let’s talk mvhr

 

so I fully understand that standard extraction systems are going to take the warm air out of the house and waste it by blowing it outside 

and I understand the principle of using the warm air to heat the incoming fresh air. 

 

What i I am having problems with is getting a grip on how to get a good system to work with our lifestyle 

we don’t want to live in a sealed up Tupperware box, I have read so many comments on how quite there new house is and I fully agree now our windows are in its silent in side, so I know what that means come May- June the kitchen window will be open and also the back door,

the door will be open to let the dogs run in and out and the windows will be open so the wife can hear the birds as she bakes a cake in the kitchen. 

 

So how do we make this situation work, 

i want. 

Good extraction from wet rooms

good extraction from laundry room

good extraction from kitchen extractor. 

 

Is there a system that will sit in very very  low mode and boost up when you enter the bathroom, or a boost switch in the laundry for when the back door is shut. 

 

Do you think Hinks mvhr is right for us or do we look at alternatives, 

 

confused as usual

i much prefer just digging holes. 

[Bitpipe]

I really don't understand where this MVHR mandatory 'sealed box' perception comes from. It's all about giving you options, not imposing anything.

 

Our house is passive standard with full MVHR and we open doors, sliders and windows year round as we please. The point is we don't have to open doors and windows to get fresh air or expel stale air as the MVHR is always taking care of that. But we can if we want, at the small cost of energy efficiency (i.e. re-heating the warm air that has escaped in winter).

 

N.B. if you open a single door or window then as the rest of our house is airtight then there is little air movement you need to open two  to get a cross draught.

 

Actually being able to keep doors & windows closed is most useful in summer. At night we open one slider a crack (in a locked position) and open the Velux at the top of the house - cools everything down nicely. During the day we try and keep everything shut to minimise warm air from outside making the house uncomfortable.

 

We don't have an active cooling system like some here (air or slab) so really need to watch overheating in summer.

 

Even if every door and window is open, the MVHR extract will still work fine - you just loose some efficiency on the heat recovery side.

 

You can configure the system to do what you want - most of us here have balanced it and figured out how to meet BR standards and then dialled it back down to a comfort level.

 

For us this is 30% fan for comfort and 50% for boost.

 

We have PIR sensors in each bathroom which trigger the boost mode, also triggers when a bathroom light is turned on (and doubles up as the trigger for the DHW re-circulation pump).

[Stones]

+1 to everything @Bitpipe has said.  We have installed MVHR in a number of houses, the first was a standard regs build back in 2003.  Leaky, poorly insulated in comparison to today, yet the difference it made to air quality inside the house, i.e. constant fresh pre warmed controlled flow air (rather than howling gales through trickle vents) and the elimination of condensation made it a must have for us irrespective of any cost savings on heating bills.

[Jeremy Harris]

+1 to both the above ^^^

 

MVHR gives you very good air quality, and reduces the heating requirement, on days when you want to keep the doors and windows closed, because of the weather outside.  If you want to open the doors and windows when the weather's fine then just do so. 

 

Our MVHR just provides background ventilation to keep the air in the house fresh all the time, and will boost up to a higher rate when it senses that the extract air is more humid, usually when we running a shower or when cooking.  If we wish, we can just press the boost button, each press puts it in boost mode for an hour, so three quick presses gives three hours of boost.

 

The house never has any condensation anywhere, clothes dry very quickly if just hung of the airer in the utility room (no need to boost to get that to happen), the house needs a lot less cleaning, as all the fresh air is filtered, and we don't have any spiders or flies in the house.

[ProDave]

And to add there is noting to stop you opening doors and windows in the summer. MVHR does not preclude that.

 

A side effect of a well sealed house with mvhr is even on a windy day, you can open one door or one window and not get a howling gale blow through from all the uncontrolled ventilation openings you have to have in a non mvhr house.

 

P.S our house does not feel like a sealed up tupperware box.

[Russell griffiths]

Thanks @Bitpipe that has answered loads of questions for me, I have been fretting about this for a while, the trouble with talking to reps at shows is you just feel they all want to flog you something. 

 

Thankyou all, put my mind at rest, I can carry on worrying about my French holiday on 3rd April again. ??

[joe90]

I agree with all above and whilst planning our MVHR asked if it was possible to have it running only when the air was stale but this is more trouble than it’s worth. For “boost” I have a humidity stat mounted in the exhaust manifold, I can set the RH level at which it comes on (Bath, shower, cooking) and when the level gets back to a set normal it simply switches off. For the very small amount it costs to run it might as well stay on, but you could always switch it off during fine weather. Just had a thought, if you switched off (by having a switch to the trickle setting) it would still come on fir boost if you wanted it too. (I might do this myself).

[Bitpipe]

A further benefit 

5 hours ago, Jeremy Harris said:

As all the fresh air is filtered, and we don't have any spiders or flies in the house.

 

Also, if you are sensitive to pollen etc then you can get higher grade filters to trap this.

 

Downsides of MVHR

- running cost :should be minimal but they're not free to run

- noise :  If not properly located, the larger units can give off vibration noise and you may get a slight drone through supply vents, although these can be minimised by incorporating a silencer.

- maintenance : the filters do need regular cleaning and occasional replacement and the heat exchanger benefits from a good clean twice a year.

- installation: can be fiddly getting the duct from each room back to the manifold / MVHR location and you need to consider how to get the larger bore insulated ducts from the MVHR to an outside wall or use roof vents. Good design early on will minimise the installation complexity and it's definitely something you can DIY and save a few grand on installation. Keeping the unit central will equalise duct runs and make it easier to balance the system but this is not always practical. Ours is in basement plant room on one side of the house and works fine.

[Jeremy Harris]

Yes, we have an F7 filter on the intake to ours, which filters out pollen and a fair bit of the smaller particulates (takes out about 70% of PM2.5s).  A useful benefit if you suffer from hay fever (as I do).  It means that I can go for days in the pollen season without needing antihistamines, which is a definite plus.

 

Ours was audible initially, but fitting silencers fixed that.  I'd recommend fitting the biggest silencers you can, as they really do make a big difference.

[joe90]

Mine is only audible when on boost in those rooms nearest the unit.

[Onoff]

17 hours ago, Jeremy Harris said:

and we don't have any spiders or flies in the house.

 

Isn't that more to do with how well the house is physically sealed. No gaps round windows, doors etc. for them to get in and doors and windows rarely left open?

[Jeremy Harris]

1 hour ago, Onoff said:

 

Isn't that more to do with how well the house is physically sealed. No gaps round windows, doors etc. for them to get in and doors and windows rarely left open?

 

 

Yes, the only place spiders get is is when we open one of the doors, usually the back door.  They used to sit in wait under the outer bit of the door, and run in as it opens, but I now squirt diluted peppermint oil around the outside doors and that keeps them away.  As we don't get flies and bugs in the house, it seems human to keep spiders out, as they will probably only die from starvation if they did get in . . .