Best location for my MVHR unit

[Adsibob]

I've only just realised (thanks to a comment by @joe90 on another thread) that ideally my unit should be placed centrally. This was not my original plan. Oops!

This is what my loft floor looks like (or will look like once the builders get around to converting the loft later this year):

In case it's relevant, this diagram is shown with:

• the party wall with the attached neighbours at the top (north);
• the street is to the right (east);
• a side passage at the bottom (south) between my house and my detached neighbours; and
• my garden is to the left (west).

 

I had planned on siting my MVHR unit mounted against the external brick wall in the eaves storage that is to the bottom right corner, as this is:

1. close to all three bathrooms in the house (one is directly under the eaves storage and the third is directly under the bathroom shown);
2. the same side of the house as the kitchen (which is under bedroom 4 but out a bit into the garden (where we are extending at ground floor)
3. not adjacent to any bedrooms or living spaces, so won't disturb anybody.

 

But if the unit needs to be placed centrally, then this really isn't central at all as it is in the corner of the top floor of a three storey house.

 

Another option is to place it in the larger Eaves storage space that is on the other side of the stairwell. That is more central although further away from all the wet rooms and very far from the kitchen. There is also no external brick wall there to mount it to other than the party wall, but that would defeat the purpose of mounting it centrally. I work from home in the "home office" most days (even before the pandemic) so the idea of having an MVHR unit so close to me is not something I'm keen on, because I have stupidly sensitive hearing and will probably hear it. That room also doubles as our guest room, so not great for guests either. The other option is in the utility room on the ground floor, that is up against the same external brick (southern) wall, but I thought it needed to go close to the roof.

 

Any thoughts?

[joe90]

Even tho I mentioned my shortest pipe route being near a guest bedroom (noise wise) you can only hear it when on boost, at all other times it’s innaudible in any room , my unit is hung from roof rafters and on rubber mounts so no noise from the up unit/fans is transferred to ceiling  joists/rooms. Location is also constrained by external vent location (mine is North wall location).

Edited February 1, 2021 by joe90

[Adsibob]

10 minutes ago, joe90 said:

Even tho I mentioned my shortest pipe route being near a guest bedroom (noise wise) you can only hear it when on boost, at all other times it’s innaudible in any room , my unit is hung from roof rafters and on rubber mounts so no noise from the up unit/fans is transferred to ceiling  joists/rooms. Location is also constrained by external vent location (mine is North wall location).

Thanks @joe90. Apologies if I've asked you this already on another thread, but which unit did you go for?

[joe90]

6 minutes ago, Adsibob said:

Thanks @joe90. Apologies if I've asked you this already on another thread, but which unit did you go for?

An Ebay special (Kingspan ) Mitsubishi lossnay unit. A real punt as it was cheap.

[Adsibob]

11 minutes ago, joe90 said:

An Ebay special (Kingspan ) Mitsubishi lossnay unit. A real punt as it was cheap.

This one https://www.bpcventilation.com/mitsubishi-lgh15-rvx?gclid=Cj0KCQiA6t6ABhDMARIsAONIYywxIlW6CPGkPqQ3nsbvoN58-Uuo_c8WXffGujQ2IyYvX4iTg6IVFnoaAmetEALw_wcB ?

 

[joe90]

4 minutes ago, Adsibob said:

This one https://www.bpcventilation.com/mitsubishi-lgh15-rvx?gclid=Cj0KCQiA6t6ABhDMARIsAONIYywxIlW6CPGkPqQ3nsbvoN58-Uuo_c8WXffGujQ2IyYvX4iTg6IVFnoaAmetEALw_wcB ?

 

Very similar, same outside by the looks of it but different model number (newer I guess). @ProDave also has the same and he is pleased with his.

[Adsibob]

2 minutes ago, joe90 said:

Very similar, same outside by the looks of it but different model number (newer I guess). @ProDave also has the same and he is pleased with his.

So did you and @ProDave ignore the bit in the specs that says not suitable for extracting from bathrooms? Or maybe that's limited to this iteration of this model.

[ProDave]

6 minutes ago, Adsibob said:

So did you and @ProDave ignore the bit in the specs that says not suitable for extracting from bathrooms? Or maybe that's limited to this iteration of this model.

Yes I have that unit.  It was a cheap ebay purchase.

 

When you drill down into the detail, my understanding was it cannot extract entirely from a humid area so no good for a swimming pool or large changing room.  But in a domestic setting ours extracts from 2 bathrooms, a kitchen and a utility room.  It is rare for more than one bathroom to be in use at once and the utility and kitchen are rarely very humid.  So the high humidity while showering is "diluted" by the other rooms.

 

It certainly does not give any issue in use and the heat exchanger core never appears to be wet or in any distress.

 

As to the question in the OP, mine is off to one side in the house not central with the shortest vent run being about 3 metres and the longest about 10 metres.  It was no problem balancing it.

[Russdl]

@AdsibobI have no practical experience as ours isn't switched on yet, still waiting on electricity, however I would have thought there would be absolutely no issues mounting it in either of those eaves spaces regarding the duct run lengths and lack of centrality to the building.

 

Whilst the bottom right option gives you an external wall to go through you say it is south facing and between two properties so potentially the intake air could get quite hot in the summer months. Your other option in the top right would mean you would have to go through the roof with your intake and exhaust. If you went for the top right option I should think you could mitigate any noise transference issues without too much difficulty.

 

 

[PeterW]

@Adsibob out of interest how airtight are you making this renovation / extension..?? MVHR retrofit into older properties is variable in its success as it needs a decent level of airtightness. 

[PeterW]

Oh and another vote for the Lossnay units. They are very good and have an enthalpy heat exchanger as standard - hence why they cannot be used in permanently wet environments. What is interesting is in winter the external intake RH is consistently higher than the extract, even from bathrooms, as it is blended with extract air from all “wet” sources which are unlikely to all be creating steam or moisture at the same time. 

[Adsibob]

1 hour ago, PeterW said:

@Adsibob out of interest how airtight are you making this renovation / extension..?? MVHR retrofit into older properties is variable in its success as it needs a decent level of airtightness. 

This is a good question and something that I have been pondering. The whole house has been gutted completely and we are installing new windows throughout (without trickle vents) and replastering, retiling and effectively redoing every single surface. I'm also putting in a wood burning stove which will be sealed with a pipe connecting it to the outside for intake of air. There is a gas fireplace that I will have to temporarily seal with a metal (fireproof) lid so that it is airtight when not in use, but that still leaves the issues of making the walls, floors and ceilings airtight, which I've read a lot about on this forum.

 

I only learnt about MVHR after I agreed the contract price with my builder, so haven't had the "air tightness conversation" with him yet. Keeping in mind almost the entire ground floor will be a solid slab with either a polished concrete floor or a porcelain tile finished floor, am I right that there are unlikely to be any air tightness issues from the ground floor? We are also soundproofing the entire party wall at ground floor level so that we are no longer blessed with the neighbours' TV whenever they watch it (which is virtually 24h a day!).

 

As for first and second floor, these will be built up with rockwell between the ceiling and floor, then a 6mm layer of rubber iso mat, then water based UFH (first floor only) then engineered wood planks or if I've run out of money by then laminate such as quickstep. So with all these buildups I'm not expecting a great deal of leakage.

 

I expect you will say that I need to tell the builder to seal all possible joins/gaps with sealant and/or tape. I haven't included that in our contract. Is it likely to add a lot to the project cost? To give you an idea of sizes, here is a table setting out floor areas and volumes:

 

GROUND	Floor area	height	volume
Zone 1	31.53	2.7	85.131
Zone 2	35.56	2.7	96.012
Zone 3	14.47	2.7	39.069
Unzoned	5.7	2.7	15.39
FIRST
Zone 4	23.3	2.5	58.25
Zone 5	11.92	2.5	29.8
Zone 6	10.365	2.5	25.9125
Zone 7	15.93	2.5	39.825
SECOND
zone 8	15.205	2.5	38.0125
zone 9	16.36	2.5	40.9
Total Area	180.34	Total volume	468.302

 

 

[Russdl]

@Adsibob is the airtightness something you can do you self? It’s very labour intensive, so it would be expensive to get your builder to do it for you, plus if they don’t pay a lot of attention to what they are doing it probably won’t be thoroughly effective. 
 

@Jeremy Harris made his own air test rig out of a car radiator fan iirc, with something like that you could find where the air leaks are and set about sealing them. 

[Adsibob]

3 hours ago, Russdl said:

@Adsibob is the airtightness something you can do you self? It’s very labour intensive, so it would be expensive to get your builder to do it for you, plus if they don’t pay a lot of attention to what they are doing it probably won’t be thoroughly effective. 
 

@Jeremy Harris made his own air test rig out of a car radiator fan iirc, with something like that you could find where the air leaks are and set about sealing them. 

In an ideal world this makes sense, but in reality it's just not feasible. Both my wife and I have full time jobs and with two young kids and no support due to the pandemic we're struggling. We have been planning this building project for almost 2.5 years and I had hoped that once it actually started all I would be doing is checking up on the builder every couple of days and ordering the various items I have decided to order myself. But it turns out my hopes were rather naïve. The ordering process is terribly time consuming (I probably spend on average a couple of hours a day chasing various suppliers to give me accurate quotes for windows and skylights and sliding doors - why that industry cannot provide a prompter and more accurate service is beyond me). Checking up on the builder is going okay, but it is a very complex project - in some ways more complicated than building from scratch because we have the limitations imposed on us by the existing building and its idiosyncrasies - e.g. this week we discovered the corbels are at different levels depending which part of the foundations one uncovers - not something any of the team expected. It also turns out my architect and structural engineer's drawings were not as detailed as I thought they were and so it's all a bit busy at the moment.

 

Sorry, rant over.

 

In due course, things will hopefully fall into place and I might have time to do it over a weekend. Or is this more of a several weekends worth of work? When you say it is very time-consuming - what are we talking about (it's a five bed house on three storeys with dimensions in the table above)? I also would benefit from understanding why this isn't a case of diminishing marginal rates or return. I appreciate airtightness improves performance of the system which in turn reaps energy efficiencies, but given the whole house is being gutted and redone with new insulation everywhere, no trickle vents or other fans, new plastering/tiling/flooring etc, will the "new" house really be that leaky if I don't specifically go over every join with mastic and/or tape? If we are talking about a 5% to 15% difference in performance I'm not sure it's worth the additional stress.

[Mr Punter]

Make sure you leave enough space around the unit to get to the filters.  Tomorrow afternoon I have the fun task of climbing around a very tight loft to swap out the filters in a Vent Axia Sentinel Kinetic plus, followed by swapping out a sewage pump in a mini pump station in the same house.  Glamorous job being a property developer!

[Russdl]

@Adsibob, it sounds like you’ve got your hands pretty full dealing with COVID, the house and suppliers, rant away.
 

We were pretty anal about it and it took a good weekend, plus a couple of evenings to check what had already been done by the Timberframe company and fill in the bits they’d missed because we felt getting as airtight as possible was fundamental to what we were trying to achieve, which is also bound to be easier on a new build. Life can be too short sometimes and I understand your frustrations so perhaps concentrate on the biggies, windows and doors could provided lots of air leaks if not installed correctly and it would seem that they frequently aren’t.