MHRV vs regular vents - decision!

TKD SC

Hi,

We're starting a new build soon (in coming weeks) and wanted to check people's thoughts on MHRV vs regular air vents (holes in the wall).

We're going timber frame, top insulation, air tightness, double / triple glaze windows etc. House is 260sqm, two stories, flat roof. Our architect is pushing for MHRV and doing lots of research. However, we're just a bit nervous of it - it's new enough to Ireland, is it a bit of a fad or is it a no brainer and you'd be absolutely crazy not to go for one?!

We're on a tight budget and trying to decide on things and this is one decision we need to make pretty soon. We are going to put in gas anyway to the house as we want some heating system there (along with a stove in kitchen) and either way have some radiators (another q's being how many radiators might you need normally vs needing in a house like with with MHRV?)

Our alternative is to just forget the whole HRV and put in regular hole in the wall type air vents for ventilating the house.

Our objective is to have a nice warm house (hence the timber frame, air tightness, window u value etc), not stuffy or windows condensing up or mould because there is no air circulating etc and decision comes down to:
Regular Air Vents or a MHRV system??

Any advise would be hugely appreciated as I'm changing my mind every day on this and just not sure what to do. I don't want to be looking back in 10yrs when every other new house has MHRV and regretting it yet I don't want to be signing up for an expensive fad when old fashioned air vents would be just as good.

Thanks very much

Simon

Juantorena

Sorry but I'm not going to help you here one bit....

We have MHRV (good airtightness) and you don't notice it. Which, I suppose, is indicative of how well it is probably working. It should be like a good referee, you shouldn't realise it's there.

Having said that, I'm not sure there are not either cheaper alternatives and/or simpler/dumber methods to do the same thing. Vents are obviously one but without the 'warming' of the incoming air. I'd love to investigate a passive, non-mechanical system which may work in our relatively windy climes. Also I'm not convinced of the theory that air taken from 'wet' areas will help heat the incoming air any better than taking it from any other room (almost). Kitchens and bathrooms do need good venting but the amount of times they are noticeably 'warmer' than other rooms is few in my experience. But that's by-the-by tbh.

To reiterate, I'm not saying the system doesn't work, it most likely is working, it's just hard to tell. Is it a fad? I personally don't think 'systemised' (for want of a better word) ventilation is a fad, but I wonder whether or not the current configuration of MHRV for domestic dwellings won't be usurped by other technologies or means.

If I was in your shoes I feel I'd consider it a severe disconnect between your (correct) concentration on insulation and airtightness (i.e., keeping generated heat in) and your consideration of essentially having open holes in the walls. It seems somewhat counter-productive and diluting your primary aims.

But budget is budget. And apologies if this has complicated matters further for you!

Good luck with your build.

MicktheMan

TKD SC wrote: »

Hi,

We're starting a new build soon (in coming weeks) and wanted to check people's thoughts on MHRV vs regular air vents (holes in the wall).

We're going timber frame, top insulation, air tightness, double / triple glaze windows etc. House is 260sqm, two stories, flat roof. Our architect is pushing for MHRV and doing lots of research. However, we're just a bit nervous of it - it's new enough to Ireland, is it a bit of a fad or is it a no brainer and you'd be absolutely crazy not to go for one?!

We're on a tight budget and trying to decide on things and this is one decision we need to make pretty soon. We are going to put in gas anyway to the house as we want some heating system there (along with a stove in kitchen) and either way have some radiators (another q's being how many radiators might you need normally vs needing in a house like with with MHRV?)

Our alternative is to just forget the whole HRV and put in regular hole in the wall type air vents for ventilating the house.

Our objective is to have a nice warm house (hence the timber frame, air tightness, window u value etc), not stuffy or windows condensing up or mould because there is no air circulating etc and decision comes down to:
Regular Air Vents or a MHRV system??

Any advise would be hugely appreciated as I'm changing my mind every day on this and just not sure what to do. I don't want to be looking back in 10yrs when every other new house has MHRV and regretting it yet I don't want to be signing up for an expensive fad when old fashioned air vents would be just as good.

Thanks very much

Simon

You are asking a very wide ranging question and cannot be answered without a lot more information and really you should be asking your architect or an energy professional to advise as there is a lot more to building a low energy house than meets the eye.
My advice is to seek out a good independent professional who will take your house plans, specifications & budget, calculate heat loss figures, advise on heating system, condensation risk, ventilation strategy etc and explain / present to you the pro/con's of each. As you say you don't want to look back in the future and regret your decision.

TKD SC

Juantorena wrote: »

Good luck with your build.

Thanks for the reply. Some interesting points. All worth considering. Decision time pretty soon!!

Simon

TKD SC

MicktheMan wrote: »

You are asking a very wide ranging question and cannot be answered without a lot more information and really you should be asking your architect or an energy professional to advise as there is a lot more to building a low energy house than meets the eye.
My advice is to seek out a good independent professional who will take your house plans, specifications & budget, calculate heat loss figures, advise on heating system, condensation risk, ventilation strategy etc and explain / present to you the pro/con's of each. As you say you don't want to look back in the future and regret your decision.

My architect is looking into all this for us, but tbh I wanted some other general advise from people with experience of heat recovery systems and what they think of them etc. I.e, is it pretty much a no brainer, where anyone doing a timber frame air tight house would be crazy to consider anything else, or is there a lot of maybes out there in relation to how good they are, cost/benefit etc. Just trying to get a feel from people on boards who might have some personal insights, so that I can take these on board as well as what my arhitect tells me...

uptowngirly

You can't really have an airtight house without MHRV because the hole in the wall vents make the house not airtight.

My honest opinion - get MHRV - or for a cheaper alternative - you could take a look at demand controlled ventilation.

Juantorena

TKD SC wrote: »

Thanks for the reply. Some interesting points. All worth considering. Decision time pretty soon!!

Simon

TKD SC wrote: »

My architect is looking into all this for us, but tbh I wanted some other general advise from people with experience of heat recovery systems and what they think of them etc. I.e, is it pretty much a no brainer, where anyone doing a timber frame air tight house would be crazy to consider anything else, or is there a lot of maybes out there in relation to how good they are, cost/benefit etc. Just trying to get a feel from people on boards who might have some personal insights, so that I can take these on board as well as what my arhitect tells me...

If your architect has the remit to investigate and propose solutions for you then I would tend to err towards what he/she is suggesting. They (should) know a whole lot more on these things than most (including me).

However what I would say is that - from my experience spec'ing and tracking down these various systems myself - one shouldn't get too hung up on them. Remember what your doing here - you're building a home within which you (and yours) will live and do all the things people do in homes.

Our regulations appear to increasingly reward system overload. So many people building (over the last decade or so) integrating so many technologies - peer pressure becomes a factor. Internet experts - and the various opinions/knowledge/experience that appear thereon - can often confuse more than enlighten....this post being a case in point, no doubt.

I'd suggest you focus on what's important to you. MHRV is probably not one of those things. Comfort, safety, running costs and budget are maybe some of the things of more interest. If you are convinced that whatever is being proposed fits into your priority list then go for it! House building can be so stressful at the best of times without having this new, additional, 'technology race' to contend with.

MicktheMan

Juantorena wrote: »

If your architect has the remit to investigate and propose solutions for you then I would tend to err towards what he/she is suggesting. They (should) know a whole lot more on these things than most (including me).

However what I would say is that - from my experience spec'ing and tracking down these various systems myself - one shouldn't get too hung up on them. Remember what your doing here - you're building a home within which you (and yours) will live and do all the things people do in homes.

Our regulations appear to increasingly reward system overload. So many people building (over the last decade or so) integrating so many technologies - peer pressure becomes a factor. Internet experts - and the various opinions/knowledge/experience that appear thereon - can often confuse more than enlighten....this post being a case in point, no doubt.

I'd suggest you focus on what's important to you. MHRV is probably not one of those things. Comfort, safety, running costs and budget are maybe some of the things of more interest. If you are convinced that whatever is being proposed fits into your priority list then go for it! House building can be so stressful at the best of times without having this new, additional, 'technology race' to contend with.

You are right to a point. But ventilation and it's importance needs to be fully understood.
When it comes to ventilation in the context of an air tight house you need a ventilation strategy to exhaust the moisture. MVHR is just one type of system to achieve this.
Comfort, safety, running costs and budget are important but knowledge on how a modern energy efficient house works should also be included to help prioritise. Hence my previous post on an independent adviser.