HRV and air flow around the house

BarneyMc

What's the best way to allow air to flow around the house with HRV... cut the doors short at the bottom to leave a gap?

893bet

BarneyMc wrote: »

What's the best way to allow air to flow around the house with HRV... cut the doors short at the bottom to leave a gap?

I think that is standard. Should be 10mm clearance.

Calahonda52

There is a passive house design detail which passes the air through the top frame

BarneyMc

My friend suggested something the other day that I just half grasped. Something to do with taking a small slip out of the back of the top of the architrave that sits on top of the door. It would be invisible unless you stood up on a chair. I guess if you did the same on both sides of the door and left a small gap around the frame it might work? Sorry but I don't know enough to know if this would work.

BarneyMc

Calahonda52 wrote: »

There is a passive house design detail which passes the air through the top frame

Only saw this after I posted!!

rampantbunny

Calahonda52 wrote: »

There is a passive house design detail which passes the air through the top frame

I've also heard of this. Would you be relying on a gap between the top frame itself and the lintel, or do you cut a slot out of the top frame (if it sits tight to the lintel)?

BarneyMc

Only guessing here but leaving a gap between the frame and the lintel sounds like the easiest way.

rampantbunny

BarneyMc wrote: »

Only guessing here but leaving a gap between the frame and the lintel sounds like the easiest way.

...provided your brickies installed the lintels at the right height which wasn't the case in my build (bit lower than planned). Bit of a cock-up but I'm sure something can be done.

If you are buying door 'kits' which I believe come pre-assembled, then rebating/cutting the architrave might be more difficult. In the past I considered installing a small vent over/beside each door but don't think it would look too good.

I've said it before and I'll say it again; when installing MHRV there has to be a definite trade-off re. noise transmission. Even if you have the proper ducting and use dedicated runs from MHRV unit to rooms (as opposed to T-ing off a central duct) , the effect of closing the door shut to isolate you from noise in the other rooms is no longer possible. Something we'll have to get used to.

BarneyMc

How does the 10mm gap at the bottom of doors look? Might be ok upstairs but not so sure I'd like it downstairs.

gooseygander

I an totally missing the point about gaps in doors regarding mhrv, can someone explain what you mean and reason for same, I will have mhrv and doors currently being hung without gaps, have I made a balls of something.

hexosan

Calahonda52 wrote: »

There is a passive house design detail which passes the air through the top frame

Do you have a link

rampantbunny

gooseygander wrote: »

I an totally missing the point about gaps in doors regarding mhrv, can someone explain what you mean and reason for same, I will have mhrv and doors currently being hung without gaps, have I made a balls of something.

You need to allow air to flow between rooms. most rooms will have only a supply or extract.. If rooms are sealed, you'll end up with either positive or negative pressure in these rooms (depending on whether you have a supply or extract respectively).
If you have a room sealed stove, and have negative pressure, it can result in 'sucking' CO from the stove and could be fatal.

rampantbunny

BarneyMc wrote: »

How does the 10mm gap at the bottom of doors look? Might be ok upstairs but not so sure I'd like it downstairs.

I was advised to leave 10-15mm. Can't say how it looks personally as I've no doors installed yet. 15mm gap at bottom might look a bit like bad joinery.

I think I'll go around the house and for those rooms that have walls that back onto quiet spots I might put a vent provided the location is a sensible distance from the input/extract vent.
Otherwise, my preference is for a gap at architrave if going non-door kit.

gooseygander

Is there not sufficient air gaps around normal door installation, with key hole, regular clearance top and bottom for door to swing comfortably, also the door arcatrave has gaps behind it where it butts the wall whet I am sure air can move through also???

BarneyMc

rampantbunny wrote: »

I was advised to leave 10-15mm.
Otherwise, my preference is for a gap at architrave if going non-door kit.

I've just ordered a load of door kits!! :mad: Why will it be more difficult if using these kits?

rampantbunny

gooseygander wrote: »

Is there not sufficient air gaps around normal door installation, with key hole, regular clearance top and bottom for door to swing comfortably, also the door arcatrave has gaps behind it where it butts the wall whet I am sure air can move through also???

That's something you'll need to calculate. But I've paid someone to design my system and he maintains a 10-15mm gap is required.

I read on another forum that standard doors can pass 70 litres/sec at a pressure differential of 15 Pa. Where does that leave you, I'm not sure.

Dardania

gooseygander wrote: »

Is there not sufficient air gaps around normal door installation, with key hole, regular clearance top and bottom for door to swing comfortably, also the door arcatrave has gaps behind it where it butts the wall whet I am sure air can move through also???

often times with modern doors, no, because they put those in-tumescent strips which expand upon the heat of a fire to seal...they need tight enough clearances I believe

rampantbunny

BarneyMc wrote: »

I've just ordered a load of door kits!! :mad: Why will it be more difficult if using these kits?

Because you'll have to cutting into the architrave. The alternative is that you leave your architrave sit out from the wall. How else are you going to leave a gap for air to flow behind the architrave - or am I missing something?

I'm thinking that you would need to router the top piece of architrave (but not the full depth as you don't want to look up from underneath and see a gap).

BarneyMc

rampantbunny wrote: »

I'm thinking that you would need to router the top piece of architrave (but not the full depth as you don't want to look up from underneath and see a gap).

That's exactly what I was thinking. I'll need to speak to my joiner to see what he says.

rampantbunny

BarneyMc wrote: »

That's exactly what I was thinking. I'll need to speak to my joiner to see what he says.

I suppose you could get fancy with the plaster work above the door (leave an indent) but using a router at the back of the architrave would be much easier.

sydthebeat

nobody thinking of sound transfer?

rampantbunny

sydthebeat wrote: »

nobody thinking of sound transfer?

..yes, but are there alternatives (hopefully no one will say trickle vents)?
If a gap is required, no matter where it is, then noise will get through. Unless there's a material that will stop the noise but allow the air...some fancy osmosis thing

rampantbunny wrote: »

I've said it before and I'll say it again; when installing MHRV there has to be a definite trade-off re. noise transmission. Even if you have the proper ducting and use dedicated runs from MHRV unit to rooms (as opposed to T-ing off a central duct) , the effect of closing the door shut to isolate you from noise in the other rooms is no longer possible. Something we'll have to get used to.

delfagio

Does anyone have a picture of what this gap at the architrave at the top of doors looks like, or a sketch of how it is done.....it sounds a bit confusing as to what it should look like???....

I don't like the sound of a 10-15mm gap at the bottom of the doors at floor level as personally I think that would look, in our great Irish tonque.....CAT. aka Sh#te. You could slide all your fingers under the door through a 15mm gap.

sydthebeat

i would be petrified what a 15 mm + gap under a door would do to toes caught in a door swing.

10-12mm is standard

if every habitable room has an air inlet from a central MHRV.... why is this gap in architrave needed at all? and why worry about air flow around a house?

ive only ever seen need for designed internal air flow where there is no central ducting system, and the extract and intake points are on opposite sides of a dwelling

rampantbunny

sydthebeat wrote: »

i would be petrified what a 15 mm + gap under a door would do to toes caught in a door swing.

10-12mm is standard

if every habitable room has an air inlet from a central MHRV.... why is this gap in architrave needed at all? and why worry about air flow around a house?

ive only ever seen need for designed internal air flow where there is no central ducting system, and the extract and intake points are on opposite sides of a dwelling

What about those areas that are not habitable rooms such as the hallway, the first floor landing, rear porch area etc. They also need ventilation and from what I've been told by various installers, there is not always a dedicated supply to these areas.
Plus how can you supply air to a room in an airtight house without giving it somewhere to escape to?
Surely your rooms are now positively pressurized, and those with extracts are negatively pressurized.

BarneyMc

Some ideas here but they might be.... CAT! :rolleyes:

rampantbunny

BarneyMc wrote: »

Some ideas here but they might be.... CAT! :rolleyes:

..you can do better than that Barney!

http://www.kulgrilles.com/

I'm in no way affiliated with this company nor pushing their products. Result of a quick google search for 'modern wall vents'

sydthebeat

rampantbunny wrote: »

What about those areas that are not habitable rooms such as the hallway, the first floor landing, rear porch area etc. They also need ventilation and from what I've been told by various installers, there is not always a dedicated supply to these areas.
.

you mean the main circulation spaces?

rampantbunny wrote: »

Plus how can you supply air to a room in an airtight house without giving it somewhere to escape to?
Surely your rooms are now positively pressurized, and those with extracts are negatively pressurized.

the rooms are not made air tight from each other.

rooms with extracts are generally left with open doors to indicate availability.

much ado about nothing in my opnion

BarneyMc

rampantbunny wrote: »

..you can do better than that Barney!

http://www.kulgrilles.com/

I'm in no way affiliated with this company nor pushing their products. Result of a quick google search for 'modern wall vents'

Snob! :P

rampantbunny

BarneyMc wrote: »

Snob! :P

You could probably make your own vent with a bit of that expanded metal over a hole in the wall barney...just tell your plasterer not to cover it over...job done

rampantbunny

sydthebeat wrote: »

you mean the main circulation spaces?
the rooms are not made air tight from each other.

True, but air must be allowed flow between areas, agreed?
And this airflow should be accommodated, not restricted. The less restriction, the less draughts. The less restriction the less pressure on the system to pull and push air.

sydthebeat wrote: »

rooms with extracts are generally left with open doors to indicate availability.

Personally I wouldn't leave the doors to the bathrooms or ensuites open. Especially after a night on the beer I'd also close the door to the utility/plant room to hide the mess.

sydthebeat wrote: »

much ado about nothing in my opnion

Fair enough, but enough of us have been told by the experts we've employed about this gap, so we have to do something about the nothing.