dMVHR or trickle vents

[HughF]

Discuss.....

 

Background: 15m3 mono pitched roof rear extension, UFH in slab on 200 PIR, 150 cavity, full fill. Triple glazed 1200 wide window one end, 1800 wide sliding door other end.

 

I'm aware that we need some ventilation under Approved Document L, I'm trying to convince the wife that we need dMVHR in this space. She doesn't like the windows open (at all, it would seem)... She hates drafts and feels the cold.

Edited June 22, 2023 by HughF

[JohnMo]

Other options are

dMEV and trickle vents trickle vents. Can be set to run with humidity control trickle vents. Super cheap to run compared to MVHR or dMVHR.

 

I just installed a Greenwood CV2GIP (dMEV), in my wife's summer house (massage room - so needs to be silent), it's 16m2. Have set to just above min speed, so about 5-6 l/sec, and pulls about 1.1 W. Stated noise is 10.1db(A). Cost £55 delivered from eBay. Has smart humidistat and smart over run timer.

 

You could set it the speed higher for building control sign off, then set to low speed.

 

 

[HughF]

dMEV = extract only?

 

so the air comes in from the trickle vents and out through the extractor…

[Dave Jones]

have a look at single room MVHR units with heat recovery. Really dont want trickle vents if you have made a big effort to air tight the room.

 

https://www.bpcventilation.com/bsk-zephyr-single-room-heat-recovery-unit

 

 

[JohnMo]

1 hour ago, HughF said:

dMEV = extract only?

 

so the air comes in from the trickle vents and out through the extractor…

I've assumed as an extension and your are asking about dMVHR etc, your existing house doesn't have MVHR. Yes trickle vent - auto humidity controlled trickle vents, so should be closed most of the time. Replace one of the existing vent fans in a bathroom or toilet with dMEV fan, ideally in close proximity to the extension.

 

 

[HughF]

12 minutes ago, JohnMo said:

I've assumed as an extension and your are asking about dMVHR etc, your existing house doesn't have MVHR. Yes trickle vent - auto humidity controlled trickle vents, so should be closed most of the time. Replace one of the existing vent fans in a bathroom or toilet with dMEV fan, ideally in close proximity to the extension.

 

 

We don’t have any vents in the house, or trickle vents in the current windows. We have two open fireplaces though….

 

I was assuming a dMEV in the wall of the extension? Is that not the correct place for it?

 

There is an upstairs bathroom that had a north facing airbrick right through the wall that we plastered over years ago as it was blowing a gale through in the winter.

Edited June 26, 2023 by HughF

[JohnMo]

If you have open fire places you are going to getting high ventilation rates already. So I would just go with humidity controlled trickle vents. No electric usage, limited energy usage heating room.

 

Humidity levels and CO2 levels are closely linked, so the only likely time for humidity to rise, is if you have a few people in room for a few hours and during the drying out phase after building.

 

So - High humidity in extension, trickle vents open, small cross flow across room out of one of the chimneys. Humidity returns to normal vents close, cross flow stops.

 

Cheap enough to install, passive activation, no electric required. Vents only when needed.

[HughF]

The open fireplaces are being replaced with a couple of wood burners, probably with external air supply into the floor void (my wife’s winning the stove argument, I’d rather take the chimney down)…

 

would trickle vents still be the best option in this case?

[JohnMo]

I think you need to step back and look at what you are planning for the whole house ventilation wise. As once the fireplace is sealed up (assume the chimney will be ventilated from outside, not inside), your ventilation for the rest of the house will be compromised; as the open fire places are really your ventilation at the moment.

 

 

[HughF]

2 hours ago, JohnMo said:

I think you need to step back and look at what you are planning for the whole house ventilation wise. As once the fireplace is sealed up (assume the chimney will be ventilated from outside, not inside), your ventilation for the rest of the house will be compromised; as the open fire places are really your ventilation at the moment.

 

 

At the moment there isn’t a plan…. Trickle vents, I guess.

 

It will be a hard sell to go for anything electrically powered. Despite my wife watching an inordinate amount of TV, she hates electrically powered things. ‘Too modern, too complicated’ 🤦‍♂️

[HughF]

OK, revisiting this thread as we’re up to lintel height and it’s time to measure up and order the windows…

 

Humidity controlled trickle vents still seem the sensible option to you? The plan is to not seal up the fireplaces, but to put a couple of small (4kW max) multi-fuel stoves in them.

 

If I go with trickle vents, is it a ‘fit them to every window/door’ scenario, or should I calculate the required size and spec accordingly?

 

We’re not going all-out nuts on the air tightness, but our brickies are pretty good and the pointing seems tight. I’ll probably tape the windows back to the reveals before d&d’ing the linings on.

[JohnMo]

3 hours ago, HughF said:

trickle vents, is it a ‘fit them to every window/door’ scenario, or should I calculate the required size and spec accordingly?

I assume English building regs have a minimum size in mm2 for a room, I would go with that. If you can fit to only one window do that.

[HughF]

They do, yes. I’ll read up on the regs and get the minimum. I’m replacing the upstairs bedroom windows at the same time, also facing the worst of the south westerly exposure. I’ll get vents fitted to those too.

[HughF]

Arghhhh, decisions decisions… my builder said ‘why go to all the trouble of paying extra for 3G then put trickle vents in them, I’d fit a dMVHR into the gable end wall’….

 

Really not sure what to do now.

[JohnMo]

Is that £3k for trickle vents - why so expensive? If that's the case do what the builder says

[HughF]

2 hours ago, JohnMo said:

Is that £3k for trickle vents - why so expensive? If that's the case do what the builder says

Paying extra for triple glazing instead of settling for 2g,  that’s what I was on about… The trickle vents aren’t much of an addition to the cost of the window from what I can see.

 

The uplift in U value between double and triple seems worthwhile for the small uplift in costs.

[JohnMo]

I would stay with your base plan 3G and humidity controlled trickle vent(s)

[HughF]

We're replacing the windows in the upstairs at the back of the house too, mainly to make them 3" smaller and remove the tiled cills, so we can gain 6" of uplift on the extension wall plate.

 

MVHR in the upstairs only, with something in the loft? There are 2 double bedrooms, a single, and a bathroom. Or should I stick with trickle vents in the bedrooms....

[HughF]

Update... had to get the windows and doors ordered, because, 2 week lead time. Banged a trickle vent in each of the opening panes of the bedroom windows (3 windows in total, each with a single opener, our bedroom has 2 windows), left the vents out of the extension windows/doors and will fit a dMVHR into the gable end wall.

 

 

[HughF]

On 12/07/2023 at 11:52, HughF said:

Update... had to get the windows and doors ordered, because, 2 week lead time. Banged a trickle vent in each of the opening panes of the bedroom windows (3 windows in total, each with a single opener, our bedroom has 2 windows), left the vents out of the extension windows/doors and will fit a dMVHR into the gable end wall.

 

 

Change of plan, will retrofit the windows with humidity controlled trickle vents...

[HughF]

Honestly, this has been the most head scratching decision on the whole extension build.... and I still don't know if I've made the right one.

[HughF]

On 19/07/2023 at 15:42, HughF said:

Change of plan, will retrofit the windows with humidity controlled trickle vents...

Change of plan, the humidity controlled vents I bought won’t fit on the window at all where the supplier has drilled/routed out for the vents.