Should I Go For Single Room Heat Recovery Ventilation

shinokampros

Is it worth installing single room heat recovery ventilation units in my house?

I have a 1980s built house, with 'hole in the wall' air vents. And is non-airtight. Would it be worth it to replace some or all of these with heat recovery units?

Some of the units I've looked at claim about 85% of the heat is retained.

MicktheMan

No point if the house is not air tight.

What problem / issue are you trying to solve?

ted1

how can it retain heat that is escaping out of the walls, windows, doors, floor and ceiling ?

Sleeper12

80s house first needs to be insulated. Attic, walls & under the downstairs floorboards. Not cheap but makes a very comfortable home.

shinokampros

The immediate problem I'm trying to solve is that I have basically a hole in the ceiling of the utility room (with a dryer) that goes straight into the extension attic. It's just the plastic vent tubing that's coming down from the ceiling. There is a big draft coming in obviously. Is there something I can do about that? To reduce the draft at least?

We have a C2 BER at the moment.

Also, re. making the house airtight and insulating, would love to do it all in one go but will probably do it in stages. We have hollow block concrete walls so can't pump the walls, have to go for the wrap. I'm looking to see if I'm better off spending that money in other places first.

There is 40mm internal insulation in already. I believe this is all over the house but I know it is downstairs and in the extension at least.

There is a gap between the insulation board and hollow block of about 15mm. There is a cold air moving through there. Where is that coming from? And how can it be fixed?

Would there be any point in getting the house wrapped without fixing that?

I'm in the process of reinsulating the attic and making the ceiling airtight. Looking at maybe replacing windows. Doors are ok. But the rest of the house I'm clueless about.

What is involved in insulation the floors? Take them up, add insulation and relay them? Can the floors be made airtight at this stage?

Am I better off going for insulating floors and replacing windows over getting the wrap?

Would anyone recommend getting a blower door test as a first step to figure out what to target if the ambition is to get to A1 for example.

Lumen

If your utility room is venting into your attic (rather than through your attic to an external vent) then that's a very big problem that you need to address.

If you have a conventional dryer, consider a heat pump condensing dryer instead. I have one in an unvented utility room (apart from a catflap) and no damp or mould issues.

C. Eastwood

https://www.boards.ie/discussion/comment/118376072#Comment_118376072

shinokampros. Please see my comments in relation to installing insulation in an existing concrete floor. - https://www.boards.ie/discussion/comment/118333383#Comment_118333383

C. Eastwood

https://www.boards.ie/discussion/2058223744/should-i-go-for-single-room-heat-recovery-ventilation

I would not instal single room heat recovery ventilation units in my house. You could invest the cost of these in making other better improvements. I block these vents in my house with a rolled up T-shirt when the bedroom is unoccupied. Having a warm house with low costs, in winter in Ireland in a house built in the 80’s is very complicated. I will try to explain some parts in simple terms.

1. Above I have given you details of how to insulate an existing concrete ground floor. It is very expensive and I don’t think it is cost effective because very little heat will be lost through the floor especially the further away from the external walls.
2. Its 27th Dec and it’s 10 degrees C outside. If we want 20 Degrees C inside- there will be very little heat loss through the ground floor.
3. You said your house is 80’s built. Back then there was a requirement to fit 1 m wide x 25 mm thick aeroboard insulation under the 100 mm concrete floor, inside the perimeter of the external walls. It may or may not be fitted in your house.
4. Your house probably has a concrete slab ground floor through out. It’s fine and leave it as is.
5. The first thing I recommend is to stop exhausting the moist air from your tumble dryer in to the attic void of the extension.
6. This will cause excessive condensation in the attic. It may cause Wet Rot or Dry Rot in the roof timbers.
7. There will be excessive draughts around the plastic ducting and also draughts from the dryer when the door is open. This hole in the ceiling must be made air tight.
8. Do not change the dryer. Vent the dryer through an existing ventilation duct in the wall. Alternatively hire a coring contractor to drill a 100 mm diameter hole in the wall to vent the tumble dryer to the external air. Ensure that they drill from the outside inward so the external plaster is not damaged.

C. Eastwood

https://www.boards.ie/discussion/2058223744/should-i-go-for-single-room-heat-recovery-ventilation

shinokampros, heat is gained, or lost in 3 ways from a dwellinghouse, but only it there is a difference in temperature between inside and outside. Let’s assume cold outside and we want warm inside.

1. Heat Loss by Radiation:- Ignore this one.
2. Heat Loss by Conduction: - heat lost through a structure. Window; Wall, Floor; Ceiling.
3. Heat Loss by Convection:- heat lost out of the house through air gaps together with draughts from outside blowing cold air in to the house through the air gaps/ draughts. Usually extremely very bad on Attic Rooms.
4. Heat loss by Convection is usually the cause of an amount of heat loss in many dwellinghouses. It is generally caused by warm air travelling out through gaps and holes in the fabric and structure of the house.
5. Concrete Ground floors usually have no gaps/ holes.
6. Timber suspended ground floors will be draughty because of the through ventilation in the void below the timber, which is necessary to prevent Dry Rot. Draughts in these floors will cause a lot of heat loss and uncomfortable draughts, but are easy and cheap to fix.
7. Walls:- gaps between external doors and frames; gaps between opening sashes and window frames; Room Vents (required by Building Regulations). Warm air rising up chimneys of open fires (can be blocked with pillow in plastic bag); draughts from wall cavity between plaster and door and window frames, and from under cill boards (can be sealed with silicone mastic). Upper timber floors- draught from the wall cavity in between the floor joists and up through the gaps in Tongued & Grooved flooring boards, and also between the flooring boards and bottom of skirting boards (can be sealed)
8. Heat loss from the house by convection through the ceiling, and the same gaps will allow cold air draughts from the attic void in to the house. (The Attic is generally the same temperature as the outside air).
9. The attic is possibly one of the biggest cause of heat loss by Convection- draughts, which are cheap to fix.
10. The Ceiling/attic is one of the greatest heat loss by Conduction, and the cheapest to correct.
11. I will post details below - of sealing gaps between the house and attic to reduce heat loss, which I posted in Boards.ie recently.

C. Eastwood

https://www.boards.ie/discussion/2058223744/should-i-go-for-single-room-heat-recovery-ventilation

shinokampros, Below are details of heat loss by Convection (moving air) between the warm house and the cold attic.

Bear in mind that it is very important to have through ventilation in the attic to reduce the risk of surface condensation. 

The holes/gaps referred to below need to be sealed air/tight to prevent heat loss by Convection from the house, and to reduce the draughts of cold air from the attic in to the house. It is best to seal these gaps before fitting insulation in the attic.

The more insulation fitted on the ceiling in the attic, will reduce heat loss from the house by Conduction, and will therefore lower the temperature in the attic, which will increase the risk of condensation, and will therefore require more attic void through ventilation 

1. In most instances the condensation in the attic is caused by moisture created in the house escaping in to the attic. 
2. Firstly, it is important to reduce the amount of condensation within the house. 
3. it is also important to prevent as much condensation created in the house from escaping in to the attic space. In doing this you will also reduce the amount of draughts from the vented attic space from getting in to the house. 
4. There are 5 main areas in most houses where air is exchanged between the house and the attic void, especially in older houses. (A) holes in the ceiling of the hot press where the pipes from the plumbing and heating pass through at this point. (B) Attic access doors that are poorly fitted and are not fitted with draught excluders. (C) Where the electric wires from the attic void pass down through the ceiling to the Fuse Board (consumer electrical distribution board) and (D) through the holes in the ceiling where the electric wires pass down through the ceiling to the electric light fitting in every room. (E) Downlights that are not air sealed above the ceiling, and /or not properly sealed below the ceiling. 
5. To reduce heat loss and draughts and reduce the amount of condensation getting from the house to the attic these holes should be completely blocked and made air tight. Downlighting should be replaced with sealed units. 
6. Health & Safety. Only persons competent in walking in the attic, should go in to the attic to carry out the sealing of these holes. No person except a competent electrician should open any electrical fittings. Expanded foam should only be used by competent persons and strictly in accordance with the manufacturers safety instructions. 
7. All of these holes could be sealed with silicone mastic —-( would be my choice of sealant.) For large gaps mastic can be built up over a few days. 
8. The attic access door should be fitted with a rubber draught excluder with some fittings to compress the rubber. Also put 100 minimum Insulation on the upper side of the access door ( could be glued on with silicone mastic). 
9. To reduce the amount of condensation in the house:- 
10. Don’t dry clothes on radiators,
11. Fit mechanical extractor in the shower/ bathroom and kitchen. Must be exhausted to the external air. Must never be exhausting in the the attic void. 
12. When cooking/ creating steam - turn on the extractor and open window. Close the kitchen door to prevent moist air escaping in to the other parts of the house. 
13. After a shower/ bath - switch on the extractor, or before you leave - open the window and then close the bathroom door behind and allow the moist air created to escape. 
14. Rooms in the attic would have other gaps and air leaks which are not mentioned above.

shinokampros

Thanks for the detailed response @C. Eastwood

Two questions:

1. Re. Floors - stupid question but how do I find out if I have concrete or wooden suspended floors?

2. Re. Condensation in attic. I have recently made this airtight and added extra insulation and there is heavy enough condensation there. I need to add insulation and rubber seal to the attic hatch. I will need to look at the other areas you mention on reducing mousture in the air. But I'm not sure that will fix the problem. What do you think about lap vents to help with this condensation?

C. Eastwood

https://www.boards.ie/discussion/comment/118381795#Comment_118381795

Skinokampros. Tap the floor with the handle of a sweeping brush - if you get a solid noise then it’s a concrete ground floor. If you get a hollow noise like a drum it is possibly a timber suspended floor. (Suspended means that the floor is not resting on the ground, and is therefore resting/ supported by the walls.

If you suspect that is timber take a look outside at the external wall of the room and look for a vent at ground level. It will be approx 9” x. 4” high. See photos.

If there are vents then these are to provide through ventilation under the floor to prevent Dry Rot. There should be corresponding vents in the outside of the opposite external wall.

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If possible, lift the floor covering to check is it a concrete or timber floor below the covering.

I think that since the mid 60’s most ground floors are concrete.

let my know what you discover.

C. Eastwood

https://www.boards.ie/discussion/comment/118381795#Comment_118381795

shinokampros. It is best to fit attic insulation on the upper side of the ceiling slabs.

Ensure that there are no holes/ gaps/ draughts which will enable air to flow from the Attic area in to the house and vice versa.

I would recommend 300 mm (12”) of insulation on top of the ceiling slab. This will give a U value of approx 0.16W/m2/degreeC/hr.

An unsulated Ceiling - slab only would have a U value of approx 2.1W/m2/degC/hr

Therefore, the uninsulated ceiling will have approx 13 times more heat loss than a ceiling with 300 mm wool insulated- as above.

The Ceiling is the cheapest element in a house to insulated compared to Ground Floors, Walls and Windows.

Now with very little heat in the attic and no damp air from the house escaping to the attic, there is still a possibility of surface condensation forming on the underside of the roofing felt in the attic.

To prevent this condensation in the attic the Building Regulations were made law on 1 June 1992, and these regulations require ventilation in the attic of all new houses built since then. Houses that were renovated should also comply with these regulations for ventilation in the attic.

In an Existing house, I would recommend cutting/drilling 75 mm dia holes in the soffit board. These holes must be fitted with plastic Fly grids at approx 1 m centres. This soffit ventilation must be fitted at both sides of the house to provide through ventilation. See photos.

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Where the insulation meets the felt - there must be a gap here of approx 25 mm to allow the attic void to be ventilated by the soffit vents.

Check the attic in damp wet winter days to ensure that Surface Condensation is not forming on the underside of the roofing felt. If the felt is dry then the attic ventilation is working.

shinokampros

Thanks @C. Eastwood

Re. Concrete/suspended floor. The house proper is concrete but the extension seems to be suspended floor. There is a hollow sound - although there are no vents at floor level to the outside. It's a tiled floor so difficult to take up. Will try and look under the sink area.

Re. Condensation, I have about 500mm insulation on the ceiling and is all airtight, apart from the hatch which will be done in the next week.

Where the joists meet the ceiling I have installed plastic rafter trays to ensure the insulation does not bloc airflow coming from the soffit.

I was looking into soffit vents and alternative to this is to make a gap in the roofing felt - where the overlap happens. I've seen people putting scrap pipe insulation into the gap and this ensure airflow come into the attic from the under the roof tiles.

This seems to be by far the easier option?

C. Eastwood

https://www.boards.ie/discussion/comment/118397299#Comment_118397299

shinokampros. Your understanding things and will now be able to sort out these problems. All of these building problems can be difficult to understand.

Most houses in Ireland since the 60’s have concrete ground floors which rest on the ground underneath.

Some concrete ground floors are supported at each end on the walls and are called concrete suspended floors. Your extension floor could be one of these and sound hollow. It could also be a concrete floor with a few inches of insulation under the concrete and would also sound hollow.

It there is no through ventilation under the extension floor, then I doubt that it is a timber suspended floor, because without ventilation Dry Rot would have the timber in a decayed collapsed state in a few years.

The best way to check if there is a any Surface Condensation in the Attic is to look at the underside of the felt on a very damp day when the external RH Relative Humidity is approx 95%. If there is no surface condensation then the roof ventilation is working.

shinokampros

Thanks for all the info @C. Eastwood - you are a fount of knowledge.

C. Eastwood

https://www.boards.ie/discussion/comment/118397561#Comment_118397561

Thanks shinokampros.

Kind Regards and Happy New Year. C Eastwood