# Mechanical Ventilation & Heat Recovery Systems Information



## Lemlin (19 May 2010)

Hi folks, 

I'm new to the site here but am presently completing a self build for a 3151 square foot two storey. 

Just wondering if someone could give me some quick information on heat recovery systems. I know there's plenty of information available but I'm keen to cut through all the BS and get to the truth. I'd also like to get people's opinions on them. I'm at sub floor level on my project and just got the pipes fitted for the central vacuum system. However, the agent from Beam mentioned a heat recovery system and said that they could do one for 7k. I've had a quick look and there seems to be plenty of information about them but I'm wondering if someone could explain in layman's terms what they do?

Bearing in mind that I am going with a geothermal underfloor heating system. Not sure if that effects it or not. Also, we have two fire places and are changing one to a stove but plan to go with one open in the sitting room. One agent did say to me that we could put a balloon in the chimney though and that would not negate the Heat recovery. Is he just saying that though to get a sale?

The agent said a heat recovery system would negate the need for vents in my house when built and would result in 80% of heat being kept. The price though is 7k which sounds steep. I priced ProAir in Galway and they said 6k which still seems steep. 

From people's experiences and knowledge, are they worth it and what way do they work? 

Also, would I need to go with triple glazing and ensure that I have an air tightness test done on the house?

I just want to make sure that if I did go with a system that my 6k couldn't be better spent elsewhere. 

Any help is greatly appreciated.


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## Superman (19 May 2010)

If you are putting in MVHR you should design your house around it - so no air vents in the windows, good draughtproofing details, no open fireplaces/stoves.
It does also render your underfloor heating slightly redundant. I'd be very wary about the idea of stuffing balloons up chimneys to get air tightness. Also, everytime you are finished with the fire, you'd have to shove a new balloon up.

Air tightness testing is required for all houses (some exceptions for developers).

Triple glazing will depend on what your BER assessor has told you. It has no effect on your decision to go with MVHR.


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## onq (19 May 2010)

You need to stop for a minute.

Take some advice from a professional competent in doing compliant work.

Consider going for the _passivehaus_ standard at least NOW as opposed to whatever your list of suppliers tell you they each can do.

Because in 2020 when you look back and realise you could have done it well, as opposed to doing it for the lowest cost and that houses built since 2013 are all to Carbon Neutral standard, you may feel a bit upset.

Measure twice, cut once - get competent professional advice - this is not just a kit of parts approach.



ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                       as a defence or support - in and of itself -  should       legal        action    be      taken.
Competent legal and building professionals should be asked to advise in                       Real Life with rights to inspect and issue reports   on     the         matters    at      hand.


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## Lemlin (20 May 2010)

I think I'll just stick to underfloor heating and have an air tightness test done on the house and then taping to ensure good insulation. The MVHR seems a bit over the top if I test the insulation in the house and ensure it is well insulated.


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## Mystic Oil (20 May 2010)

Just to add to the points that Superman made, there are a (limited) number of heating stoves on the market that are "room sealed" and therefore don't impact on airtightness.


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## onq (20 May 2010)

Lemlin said:


> I think I'll just stick to underfloor heating and have an air tightness test done on the house and then taping to ensure good insulation. The MVHR seems a bit over the top if I test the insulation in the house and ensure it is well insulated.



Lemlin,

Without trying to ludgeon you to death with logic, you do not appear competent to assess the matter.

Yet if you don't have a main contractor on board on a self-build, you are deemed to be the main contractor under Health & Safety regulations.

Please the Self Build Faq http://www.askaboutmoney.com/showthread.php?t=126261

Please note that only competent people should carry out work to a building.

Please ask some competent person to advise you on this matter.

Its not some figment of my fevered imagination - its the law!



ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                        as a defence or support - in and of itself -   should       legal        action    be      taken.
Competent legal and building professionals should be asked to advise in                        Real Life with rights to inspect and issue reports    on     the         matters    at      hand.


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## RKQ (22 May 2010)

Heat recovery in lay mans terms:-
Basis idea is to suck out damp moist stale air from kitchen, bathrooms, bedrooms etc. Then suck in fresh air from outside. This ventilates your house.
The clever part is to use the warm moist stale air to heat the cold fresh air by putting the wet warm air through a heat exchanger.
Most systems add filters to clear the fresh air - good for ashma sufferers etc.

Its important to have an airtight house and to regularly clean or replace the filters.

As above, do your homework and get professional advice. If using a stove, get one that is fed air directly from outside, via a pipe. 

The rubber "baloon" cost €20 -€50 and is reusable. Its main function is to prevent a draught in an unused fireplace. I don't belive it was invented for use in an airtight house.


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## onq (22 May 2010)

No, it wasn't as far as I can see.
There wouldn't be a chimney open to air in an "air tight" house.
One might thank that the balloon is to stop the chimney sucking air out of the house.

The opposite seems to be the case - when the fire is unlit, the chimney is a source of open entry for cold air from outside.
Anyone sitting opposite an open unlit fireplace with a chimney will confirm you can get a blast of cold air from it - its not venting air, its supplying it.
Cold damp air from outside is more dense than warm air inside - gas expands when warm, becoming less dense - the colder dense air displaces the air inside the house and moves down the chimney creating a draft.

[broken link removed]

A similar principle, but using laminar flow that follows a surface, occurs at windows. The window, being colder than the room air, accepts heat from it,.
The air gets colder and becomes more dense and starts to descend along the pane of the glass in a laminar flow that makes your feet cold on the far side if the room - unless you have a radiator under the window to counteract this.
Laminar flows tend to remain coherent along a surface and not disperse.

http://www.commercialwindows.umn.edu/issues_hf4.php

So you can see that placing heat sources properly can help combat drafts from glazing.
Also a highly sealed house may give rise to problems with open fires unless there is supply air.
It pays to consider a building "in the round" and ask somebody competent for advice - it brings good results.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                         as a defence or support - in and of itself -    should       legal        action    be      taken.
Competent legal and building professionals should be asked to advise in                         Real Life with rights to inspect and issue  reports    on     the         matters    at      hand.


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