Green Building Forum - MHRV worth it? Tue, 19 Dec 2023 08:26:44 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=260986#Comment_260986 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=260986#Comment_260986 Sun, 03 Sep 2017 12:09:05 +0100 Dickie
The facts:
1. House is a roomy 1965 4 bed detached with GCH, CWI, double glazing and an open fire place (intend to block it up).
2. Four occupants, two of whom are teenagers who love the shower, one off to uni.
3. The kitchen has a very good extractor hood, but the bathroom hasn’t. We open the window.
4. We have a condensation and mould problem.
5. Bedrooms are smelly and stale in the mornings.
6. Wife gets hayfever and kids have respiratory ailments which may be caused or exacerbated by mould spores and stale air.
7. I used to work as a kitchen and bathroom installer so although unqualified, am proficient, know my house and willing to do it myself.

A simple humidistat controlled bathroom extractor seems the obvious answer but I’m tempted by a MHRV system. The heat recovery feature appeals to my environmental sensibilities, and solves the stale air issue and just makes a lot of sense. But after reading this forum these systems seem fraught with complexity and it’s thousands rather than hundreds of ££ and I have a few questions that google has been unable to answer. (I’m unwilling to ask manufacturers as I think they will tell me it’s all wonderful.) So I’d like some real world answers to the following questions:

1. Is it cost efficient for the mild UK Midlands climate? I’ve read they’re better suited to climatic extremes.
2. How does it integrate with existing cooker hood?
3. Is there a manual override or auto sensor to cope with large amounts of steam from cooking and showering? If so will input rooms get an unwanted blast of fresh air at the same time?
4. Is it ok to turn it off during summer days? We’re human, it’s nice to leave doors open in the summer, or on mild days to let the dog in and out. But would be good to switch it back on overnight. I will probably forget to do this.
5. Could redundant chimney flues be used as part of the ducting system? One TO open fireplace in living room and one FROM an old back boiler now positioned above fridge freezer.
6. Is it possible to have a system designed professionally, but install it myself?
7. Is the design and install restricted/controlled by building regs?
8. Can you have washable rather than replacement filters?
9. Are there conditions in which it is ok to turn it off or have timer settings for when the house is unoccupied during the day, or for holidays?

I suppose I’m asking how clever are these systems? Apologies for the long post, but I’m a firm believer that systems should be designed for fallible, contrary and forgetful humans with diverse requirements, not a one-size fits all for perfectionist engineers, so I’m just trying to cover all my bases!]]> MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=260989#Comment_260989 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=260989#Comment_260989 Sun, 03 Sep 2017 13:02:38 +0100 ComeOnPilgrim MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=260990#Comment_260990 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=260990#Comment_260990 Sun, 03 Sep 2017 13:03:44 +0100 ComeOnPilgrim MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=260994#Comment_260994 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=260994#Comment_260994 Sun, 03 Sep 2017 13:33:44 +0100 djh Posted By: Dickie1. Is it cost efficient for the mild UK Midlands climate? I’ve read they’re better suited to climatic extremes.
I don't really know. Compared to what? You might consider a PIV or MEV system instead.

2. How does it integrate with existing cooker hood?

Typically, it doesn't. Either you keep the hood as is or modify it to be recirculating and block up the external duct.

3. Is there a manual override or auto sensor to cope with large amounts of steam from cooking and showering? If so will input rooms get an unwanted blast of fresh air at the same time?

Some units have that facility. Personally we don't find it necessary but your circumstances may be different. MVHR is balanced so yes the supply air increases when the exhaust air does. Viewing it as an 'unwanted blast of fresh air' is probably not terribly realistic or helpful.

4. Is it ok to turn it off during summer days? We’re human, it’s nice to leave doors open in the summer, or on mild days to let the dog in and out. But would be good to switch it back on overnight. I will probably forget to do this.

Yes, we leave windows and doors open sometimes in the summer for our cats. We don't bother turning the MVHR off since ours is self-balancing and doesn't mind and the 26 W it consumes is provided by our PV panels. I believe some units can have switch contacts that turn them off when particular windows or doors are opened.

5. Could redundant chimney flues be used as part of the ducting system? One TO open fireplace in living room and one FROM an old back boiler now positioned above fridge freezer.

Yes if they are sensibly placed. Duct design is a major issue, particularly in an existing house, unless you can use a 'ductless' system like the Fresh-R. One aim is to keep duct lengths short, especially those from the unit to the external air.

6. Is it possible to have a system designed professionally, but install it myself?

Yes, that's what I did.

7. Is the design and install restricted/controlled by building regs?

In a new house, yes. I don't know about adding a system to an existing house.

8. Can you have washable rather than replacement filters?

Yes, mine are. It depends on the brand of MVHR and also on the filter type. Pollen filters are paper I believe so not washable, for example.

9. Are there conditions in which it is ok to turn it off or have timer settings for when the house is unoccupied during the day, or for holidays?

Yes. You will need to look at individual units to see what kind of control is sensible. When you turn mine 'off' for example, it still runs at 50 m³/hr to keep the air in the house and ducts fresh. You can really turn it off from the front panel but are not supposed to turn it off and on just by switching the mains off.

HTH, Dave]]> MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261002#Comment_261002 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261002#Comment_261002 Sun, 03 Sep 2017 15:33:11 +0100 tony
Sounds to like you could diy install it too.]]> MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261005#Comment_261005 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261005#Comment_261005 Sun, 03 Sep 2017 15:46:14 +0100 Dickie MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261011#Comment_261011 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261011#Comment_261011 Sun, 03 Sep 2017 17:28:05 +0100 RobL We have a similar situation - 4 bed 1963 house, 4 people, 2 of them kids. GCH + DG + an open chimney originally.
We did an airtightness test, then fixed the worst of the leaks, then fitted MVHR maybe 3 or 4 years ago. All diy. It's not hard tbh, and you know your house better than a pro does.

We had originally intended turning it off for summer - but we don't because:
"only" 13W mean power consumption
it keeps flies out of the house
less bother than opening & closing stuff all the time

We don't integrate with existing stuff in the house - just extract from the kitchen & bathroom, input to lounge & 2 bedrooms. We have an existing kitchen extractor, that gets used rarely. I retro-fitted a flap valve to it for air tightness.

The filters *can* be washed - but our inlet one is always grubby & never as clean as new. I cut out a new one from a roll I bought, and swap the material over every time.

I definitely recommend getting one with a humidity sensor built in, and preferably with CO2 too. These will allow the unit to boost after a shower/cooking/drying clothes indoors/extra people (we have no clothes drier, but stuff dries fine with MVHR). We have a vent axia sentinel plus BH(H=humidity), with add on CO2 sensor.

While you could use a chimney, I'd be cautious unless designed for it somehow. Most units expect inlet & exhaust to be around 2m apart facing the same way, so there's no pressure difference. The last thing you want is the airflow to be dependant on how windy it is.

If you intend fitting it in your loft, make sure it will go through the hatch!

We went for oversize pipes (150mm and 200mm diameter), which keeps the air speed low, and makes it very quiet.]]> MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261012#Comment_261012 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261012#Comment_261012 Sun, 03 Sep 2017 18:39:47 +0100 tony MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261013#Comment_261013 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261013#Comment_261013 Sun, 03 Sep 2017 20:45:29 +0100 djh

What an annoying website this can be.

edit: I'd just typed some useful info [I thought]!]]> MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261016#Comment_261016 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261016#Comment_261016 Sun, 03 Sep 2017 22:06:10 +0100 tony MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261017#Comment_261017 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261017#Comment_261017 Sun, 03 Sep 2017 23:20:49 +0100 djh MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261021#Comment_261021 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261021#Comment_261021 Mon, 04 Sep 2017 08:40:28 +0100 SteamyTea You don't say how 'leaky' your house is.
This will make a difference to the heat recovery performance.

You could, as an experiment, try out a cheap single room unit, say in the bedroom most affected. Make sure the door is reasonably sealed and the windows fit well.
Then see if there is a noticeable improvement.

And don't air dry clothes inside.]]> MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261061#Comment_261061 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261061#Comment_261061 Mon, 04 Sep 2017 19:54:04 +0100 Dickie
The ventive heat exchanger is actually inside the chimney, but more useful with older style properties with open fireplaces in the bedrooms as well as downstairs.

RobL sounds like your situation is very similar to ours. Could you give me an idea of cost?

SteamyTea the obvious leaks are going to be the fireplace, toilet overflow pipes, pantry air brick - oh yes and the massive hole the cavity wall insulation installer insisting on cutting in the living room wall because of the presence of an open fire place! (oh the irony) Otherwise only a pressure test will tell me for sure.

I've got a surveyor from Envirovent coming on Thurs 14th. I'll let you know the result.]]> MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261065#Comment_261065 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261065#Comment_261065 Mon, 04 Sep 2017 22:41:28 +0100 RobL MVHR box £1500
Pipes etc £800
add on CO2 sensor £150
manpower.... lots, but "free"

Vents to bedrooms were easy, the pipes are in the loft.
We have just 2 vents downstairs - one in the kitchen (extract), and one in the lounge (inlet). These are the hardest to route, and both use rectangular plastic pipe to fit into upstairs cupboards - we have a few of these, guess it was the thing in the 60s. Here's a link to the rectangular pipe stuff I used:
https://www.dealec.co.uk/acatalog/220x90mm-flat-ducting-fittings-accessories.html
In the loft I used 150 and 200mm dia round metal pipe.

Leaks - EVERY SINGLE one of the items listed leaked:
Front door, back door, keyholes & draft excluders
All wall sockets in our house break through to the cavity. That is, the mains cables run in the cavity! I used tescon tape and or silicone sealant inside the boxes.
Upstairs light fittings.
Upstairs and downstairs skirting board. I used silicon sealant (we have wooden floors).
Between upstairs and downstairs, ie under the floorboards upstairs, there is no plaster on the wall, and our breezeblock leaked a lot. In fact there were holes right through to the cavity there. I used squirty foam and lots of it, ahh fun times.
All kitchen / bathroom pipes that are hidden had big gaps.

While it might seem a lot of stuff, you can tackle it bit by bit, if you know what to do. Here's a link to what I did:
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=7396&page=1#Item_0

Fitting the mvhr will make your home more pleasant, and maybe reduce ailments, and slightly cheaper to run. Fixing the above leaks will make it cheaper to run again.]]> MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261114#Comment_261114 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261114#Comment_261114 Wed, 06 Sep 2017 22:52:37 +0100 Dickie MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261244#Comment_261244 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261244#Comment_261244 Fri, 15 Sep 2017 08:25:49 +0100 Dickie If I want MHRV I have to submit a floorplan and they will 'tell me' where the ducts should go. Might be entertaining, so I'll give it a go.

In the meantime, can anyone tell me where and why the ideal location for input vents is? Middle of the ceiling? as far from the door as possible? near or away from windows?
Ta very glad.]]> MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261246#Comment_261246 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261246#Comment_261246 Fri, 15 Sep 2017 08:45:41 +0100 gravelld MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261249#Comment_261249 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261249#Comment_261249 Fri, 15 Sep 2017 11:05:44 +0100 Simon Still Posted By: DickieIn the meantime, can anyone tell me where and why the ideal location for input vents is? Middle of the ceiling? as far from the door as possible? near or away from windows?

My design was done for me but looking at my vent positions they're generally towards the corner of the room furthest from the door. That makes sense as the door's where the air will be exiting or entering and you don't want any 'dead' areas.]]> MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261252#Comment_261252 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261252#Comment_261252 Fri, 15 Sep 2017 11:55:30 +0100 djh MHRV worth it? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261257#Comment_261257 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15273&Focus=261257#Comment_261257 Fri, 15 Sep 2017 13:14:33 +0100 Greenfish
I do wish some of mine were just a little more into the room, and in hindisght in front the windows (furthest from the door) could be a better location. I suspect that possible routing of duscting will have an impact.

What DJH said too.

Oh and back in 2014 getting quotes for MVHR was a nightname, so slow to respond, so lacking in detail. Hard to believe that actually wanted to sell anything. I hope better now, but I expect that patience and persistence still needed.]]>