MVHR - Mechanical Ventilation with Heat Recovery - pros and cons

galwaytt

Frequent Poster
Messages
571
...I'm not up with the technical issues associated with air tighteness etc but I have been told that it is possible to achieve high levels of air tightness with a block build - obviously if the builder does his job! I suppose the real issue here is if not going with an airtight timber frame of SIP system is MVHR still worthwhile?

A secondary issue here relates to the Building Regs and the installation of solar panels. I was of the view that if you installed a renewable heat source like a geothermal heat pump this obviated the need to go with solar panels, at least that is what I have been advised. Thanks in advance
You've caught my eye with mention of SIP (it's what I do), so a few things there:
1. Even built well, unless you undertake a specific airtightness 'programme' in a block build, it will not be airtight. This is simply a reflection of the properties of blocks/etc. You can of course make it airtight, but that is a distinct separate task, and trade. And it brings a cost with it.
Another limitation is that you're only talking about walls - the roof is another huge issue, as is the connection of it, to the walls. Again, you're talking about time and materials. And , again, money. As you probably know what a SIP is, you'll know this is a non-issue in a SIP system.

2. As to the value of going with MHRV etc, well the fact is, that airtightness is now a measured requirement, so if you have a particularly good reading, you're probably going to need it anyway. Simply put, the choice of your building method shouldn't be influencing your decision on the MHRV, as your requirement for airtightness is the same, irrespective of the build type you choose.

3. In any modern house, built to a high standard, and working well, it's requirement for heating will be (relatively) low. This being the case, heating system choices, and their costs, need to be considered even more carefully than before. I like solar, because, in a new build, it is not a big cost as part of a new system, and imho, it does make a measurable contribution. As usual, YMMV and all that :)

4. I'm still not personally convinced about heating systems that are heavily reliant on electricity. Again, this is not a reflection on the systems themselves, but more the cost of electricity itself.
 
R

rugbyguy

Guest
Hi I recently installed a heat recovery system into my home. Initially I intended to do a diy job on it myself as posts here say it's diy friendly but decided to get a crowd home heat recovery to do it for me as i was busy working. Glad i did in the end as they had two ductors that spent 4 days doing the work so i greatly under estimated the amount of work on rigid ducting and the expertise required to do the job right. You pay for what you get and if i done the job i would have done a cheap job far less professional to what the guys done.
 

buyingabroad

Frequent Poster
Messages
159
I have spent a fair bit of time researching MHRV and concluded it's not the way to go for me. Will be going with a Mechanical Extract Fan system that's humidity and presence sensitive with ducts extracting moisture from wet rooms. In habitable rooms, I plan to install either hole in the wall / trickle vents in windows, both of which would be humidity sensitive.
 

Patrick2008

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Messages
110
Hi All,

Very good thread and some very valid comments. Can I ask a question which is related to what we are discussing? Is timber frame the way to go in lieu of blockwork? e.g timberframe with 50mm cavity and external blockwork with render. I know of some people who are using cavity wall with 80mm cavity insulation and sand cement, urethane board mushroom fixed to interna face of external walls.

I would have imagined timber frame is the way to go but this all depends on the quality of the timber frame contractor etc.
 

Buildright

Registered User
Messages
37
You can't ask a qustion comparing timber frame versus masonery. Its can't be done. Quality control is a big problem on our domestic building sites and generally results in a low quality product.

I have 2 specifications, both deliver near passive performance levels at slightly over conventional build rates. Performance levels are walls 0.14 u-value. I have other standards at 0.16 and 0.18. Airtighness is 1 air change @50pa underpressure. MHRV is used to run at 0.75 air changes per hour wit polyetheelenr ducts. Heating oil boiler with underfloor to tiled areas and 2 towel rails on a seperate circuit. 5m2 solar evc tube. 1000l buffer. room sealed stove.

One is masonery, 250 mm wide cavity masonry, precast first floor, cellulose filled double rafter roof with cellulose fill and softboard racking. Foamglass and Quinlite inner leaf starter blocks on standard rising wall.

Two is timber frame, vapour diffuse to outside: aquapanel renderboard rainscreen, panel vent racking board, 220 stud with 75 rail, cellulose filled, osb inner board, insulated services cavity, osb substrate, plasterboard. On an insulated formwork EPS raft.

Heres where the fun starts..... Firstly, I need to build a thermal bridge free rising wall/edge beam and get the Radon barrier right. I need to get the building windtight from outside, softboard on the roof does this. Then when the windows are in, I get the inside airtight using OSB rather than intello. Then the trades come in and poke holes everywhere... thats why I use OSB.

There is no difference in performance if you detail the build well and have good quality control on site. The build spec I have selected, is the optimum level which balances enhanced performance against cost. It is an affordable spec which delivers a thermally stable, good quality indoor climate and healthy air, with a spec designed for longevity and very low running costs. The spec, its devised using a systems approach. What is saved on heat pumps is simply put into insulation. Its common sense, heat pumps with a payback of 20 years vs insulation and airtightness with a payback of 3.

Running costs can be calculated from your PHPP (passive house planning package) MHRV will half your space heating bill. The house to the above spec, is a celtic tiger design, two storey with gables and dormers and stuck on stone. Perched on a hill. ' hey look at me' you know the type. At about 250 square metres it will cost about €700 a year for space heating and hot water, pumps etc.

MHRV uses a pair of Santos units with solid ducts (no flexis or flatpacks). two 25w fans in each running continuously.
 

galwaytt

Frequent Poster
Messages
571
Hi All,

... Can I ask a question which is related to what we are discussing? Is timber frame the way to go in lieu of blockwork? e.g timberframe with 50mm cavity and external blockwork with render. I know of some people who are using cavity wall with 80mm cavity insulation and sand cement, urethane board mushroom fixed to interna face of external walls.

I would have imagined timber frame is the way to go but this all depends on the quality of the timber frame contractor etc.
You can't ask a qustion comparing timber frame versus masonery. Its can't be done. Quality control is a big problem on our domestic building sites and generally results in a low quality product.
And buildright has nailed it on the head, in one. Naturally, I have an interest, as I build homes in a timber based system, but the single biggest issue is, and will continue to be, quality. Good materials, poorly assembled, still gives a poorly built house.

The current downward ratcheting of prices, is only going to end in tears, as you always, always, get what you pay for. Get a quote for X, and then get the job done for x/2 - then, you don't need to be scientist to figure out that that saving is coming from somewhere..........and it isn't your future energy bills !

When we did our accrediation with the BRE, a major thing for them is 'How do you manage quality on-site' ? And every second visit that they make to us is to a site, to check. For us, the simple way to control quality, is use factory-employed staff directly - we don't use subbie's - for too long, they've been paid on a per sq ft basis (and bring your own fixings ! :eek: ), and that only gets you one result.........


Back on-topic, btw - quick question - if people are considering NOT using MHRV, I'd love to know what they ARE planning to use, in lieu.......
 

feileacan

Registered User
Messages
29
Mhrv

re topic: has anyone any experience with or comment on finewire HRV? am considering this on grounds of cost and simplicity
 

buyingabroad

Frequent Poster
Messages
159
A thought struck me recently. Why do MHRV systems need filters (and need regular replacing of those filters) while the old hole in the wall and demand/humidity driven ventilation systems don't. Is it to keep debris/insects out of the fans to prevent damage or is it an air quality issue?
 

L Driver

Registered User
Messages
11
re topic: has anyone any experience with or comment on finewire HRV? am considering this on grounds of cost and simplicity
Hi,
Looks very impressive and simple. Will be looking more into it. I think it will be the way to go
 

sunnyside

Registered User
Messages
46
Really interesting posts. I was hoping to reignite the discussion as we are now in 2013. Have any of the original contributors any updates? Or does anyone else have a view ?

Are heat recovery systems more advanced now?

I am in the midst of choosing a builder for a 2300 sq foot house and today the builder who are leaning toward told me he thought they weren't worth the money. It goes against my research to date.... I'd love to hear any opinions
Cheers
 

lowCO2design

Frequent Poster
Messages
575
I am in the midst of choosing a builder for a 2300 sq foot house and today the builder who are leaning toward told me he thought they weren't worth the money. It goes against my research to date.... I'd love to hear any opinions
Cheers
there not worth the money when a builder cant achieve a decent standard of air-tightness!

if you dont have a performance spec for your builder forget about it.

btw do you have a provisional BER done?
 

sunnyside

Registered User
Messages
46
Thanks very much for the reply.

The site we have bought has just the foundation poured and services in so, no Ber yet.

What do you mean by a builders Performance spec?

Any other tips when choosing a builder ?

Am I to take it that your a fan of hRv systems?
Any and all advice appreciated.

Thank you
 

Lanni

Registered User
Messages
8
Mvhr

It is important to clarify exactly what you want from the building. I am not sure what details are included in your drawings, but sometimes you need a list of specifications.It is better to have everything agreed before engaging with the builder.
A MVHR system is great if you have suitable insulation and air tightness levels in place. Current regulations require an air tightness minimum level of 7m3/hr/m2, but you really need to be under 3m3/hr/m2 for the system to operate more efficiently. Otherwise you are looking at trickle vents, extractor/intermittent vents and permanently open vents for rooms with combustion appliances.
The preliminary BER or DEAP calculations is a condition for certain County Councils which must be issued with the commencement notice. It serves a vital purpose in that from the outset you are confident that the design is compliant with the current building regulations.
 

lowCO2design

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Messages
575
Thanks very much for the reply.

The site we have bought has just the foundation poured and services in so, no Ber yet.


  1. What do you mean by a builders Performance spec?
  2. Any other tips when choosing a builder ?
  3. Am I to take it that your a fan of hRv systems?
Any and all advice appreciated.

Thank you
1.:eek::eek::eek:
am in the midst of choosing a builder for a 2300 sq foot house and today the builder who are leaning toward told me he thought they weren't worth the money.
your choosing a builder and you have mentioned detail tender/constriction drawings and you dont know what a performance specification is.



2. you need an architect to specify and detail the drawings so there is no squirming in an builders price. you need an engineer because you dont know what foundations/floor you bought, and you need to do a BER assessment at a minimum, so you can comply with building regulations

3. HRV is the least of your worries as others have said - the road your heading down seems more like this


i wish you all the best
 

vicar1

Registered User
Messages
5
HRV in old house

Hello!
Looking for some advice please.
Can you install HRV in an old house, or are there any 'stand alone' type units that could be installed in the damp / hot rooms such as bathrooms / kitchen?
Any advice much appreciated - and are they worth the money in terms of heating bills and comfort?
Thanks!
 

Leo

Moderator
Messages
10,661
Can you install HRV in an old house, or are there any 'stand alone' type units that could be installed in the damp / hot rooms such as bathrooms / kitchen?
How air-tight is the house? This will play a significant role in the efficiency of MHRV.
 

David Pritchard

Registered User
Messages
1
I know this is an old thread, but I thought I'd add my experience of HRVs since it might help somebody.

I have a HRV unit in a dry climate (Spain) and I'm an absolute convert to it. I think the benefits of these systems are actually undersold - I get the impression that the idea is so new, that even the businesses selling it don't realise all the implications of living with these systems. Most articles focus on the energy-saving aspect, and conclude that it may not be worthwhile in some climates (for Ireland I imagine you'd get your money's worth in a few years). But even in a moderate climate such as Spain, I reckon that if you add up all the benefits, it's a no-brainer.

Apart from the obvious point that an HRV/ERV squares the circle of insulation and good ventilation, which are otherwise contradictory objectives, here are the plus points I've noted:


- Indoor pollution and smells are expelled. Waking up in the morning with fresh air, but without draughts and cold from open windows, is just great.

- Outdoor pollution is filtered. This is a big deal in cities. My filters were filthy black when I took them out after 2-3 months. I have photos of the filters but I'm not sure how to upload them.

- No bugs! Living next to some gardens, I usually get mosquitos for about 11 months of the year, believe it or not. The filters trap them all.

- Less noise. If you don't have to open windows to ventilate, you keep the noise out. There are some annoying tropical birds in the gardens next to the apartment that really make a lot of noise.

- Less humidity indoors. Obviously this depends on the outdoor climate. Ireland is more humid in general so you'd need to check this.
 

npgallag

Frequent Poster
Messages
171
Any recent reviews on MVHR systems installed in Ireland. I am currently looking at a Beam system for new build.
 
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