Green Building Forum - Retrofitting continuous ventilation after fitting new windows Wed, 03 Jun 2026 06:06:22 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290819#Comment_290819 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290819#Comment_290819 Thu, 05 Aug 2021 11:05:23 +0100 Shevek
The most cost-effective method I think is to add trickle vents (easy retrofit in our case because there is a roller shutter above each window with an internal access panel they can be fitted into) and then swap the current intermittent extract fan in the bathroom for a continuous extract fan + humidity booster sensor. All internals doors have a 5-10 mm undercut.

Am I taking the right approach?

My main concern is noise. What is the quietest fan on the market and what can we do to make sure we minimise noise? A suspended ceiling in the bathroom to provide sound-proofing to a fan unit is definitely on the cards; it needs one anyway because it's currently a concrete soffit and attracts condensation because if it's surface temperature.

We may also fit a hot water cylinder with integrated heat pump of some description in the little room next to the kitchen. Could that factor into a ventilation strategy?

I did also wonder if we could fit a dMEV fan unit (e.g. Brookvent airstream) but fitting ductwork at a later date.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290823#Comment_290823 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290823#Comment_290823 Thu, 05 Aug 2021 13:44:02 +0100 Mike1
Ideally you'd want to be fitting an MVHR unit - maybe in the laundry. ICW this and your other thread on suitable heating, this thread may be worth a read: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17129]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290825#Comment_290825 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290825#Comment_290825 Thu, 05 Aug 2021 14:25:26 +0100 Shevek
My intention would be to fit acoustically attenuated trickle vents like Brookvent's SM Acoustic.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290830#Comment_290830 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290830#Comment_290830 Thu, 05 Aug 2021 20:38:56 +0100 Ed Davies Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290839#Comment_290839 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290839#Comment_290839 Fri, 06 Aug 2021 08:40:53 +0100 PeterStarck Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290849#Comment_290849 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290849#Comment_290849 Fri, 06 Aug 2021 13:21:09 +0100 fostertom
Ventilation guru Peter Rickaby, who's done lots of work on IAQ in far-from-ideal housing like Thamesmead, for buildings like yours swears by centralised MEV (MRHV but without the ducted intake or heat recovery!) https://www.vent-axia.com/range/centralised-mechanical-extract-ventilation-mev, as a lot cheaper and tenant-foolproof.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290856#Comment_290856 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290856#Comment_290856 Fri, 06 Aug 2021 16:10:05 +0100 djh Posted By: fostertomYou can get trickle vents that have a humidity sensor that shuts them automatically when not needed.
But if Shevek fits an EAHP then surely any sensor in a trickle vent will see more of the external air's properties as it is sucked in? And with an EAHP they'll need to be always open in any case?

Ventilation guru Peter Rickaby, who's done lots of work on IAQ in far-from-ideal housing like Thamesmead, for buildings like yours swears by centralised MEV (MRHV but without the ducted intake or heat recovery!)

"Sorry, the page or file you were looking for couldn't be found
"We've recently redesigned the Vent-Axia.com website"

But that's essentially how an EAHP behaves isn't it, as far as ventilation goes? It acts as an MEV unit.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290863#Comment_290863 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290863#Comment_290863 Fri, 06 Aug 2021 17:24:45 +0100 fostertom works for me.

Posted By: djhsurely any sensor in a trickle vent will see more of the external air's properties as it is sucked in
So you'd think but apparently they've solved that, whether 'sucked' in (by fan, or more usually by passive stack effect) or 'blown' in by wind. Hopefully the fan's humidistat would fairly well sync with the trickle vents' stats - at any rate you'd want to have whatever kind of air inlet open only at times of ventilation need.

This is an alternative to
Posted By: djhShevek fits an EAHP
]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290867#Comment_290867 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290867#Comment_290867 Fri, 06 Aug 2021 20:09:05 +0100 djh Posted By: fostertomhttps://www.vent-axia.com/range/centralised-mechanical-extract-ventilation-mev
works for me.
It works for me too, but that isn't what you posted. It was another example of including a trailing punctuation mark in the URL :cry:]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290868#Comment_290868 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290868#Comment_290868 Fri, 06 Aug 2021 20:17:10 +0100 djh Posted By: fostertom
Posted By: djhsurely any sensor in a trickle vent will see more of the external air's properties as it is sucked in
So you'd think but apparently they've solved that, whether 'sucked' in (by fan, or more usually by passive stack effect) or 'blown' in by wind. Hopefully the fan's humidistat would fairly well sync with the trickle vents' stats - at any rate you'd want to have whatever kind of air inlet open only at times of ventilation need.
Have you got a link (without a comma :bigsmile:) to such a product?

This is an alternative to
Posted By: djhShevek fits an EAHP

Sorry, I don't understand this at all. The whole discussion is in the context of Shevek's "We may also fit a hot water cylinder with integrated heat pump of some description in the little room next to the kitchen." or even his continuous extract fan.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290871#Comment_290871 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290871#Comment_290871 Fri, 06 Aug 2021 21:11:25 +0100 bxman

How many occupant and what volume is the flat ?

how many months is it necessary to keep the windows closed .

Are you able to dry any washing outside the envelope ?

How much moisture is generated by cooking ?

if you were on your own you might find you could control the R H and have an acceptable air quality without the need for any forced air movement

My experience is that if you can eliminate air movement you will feel 2 degrees warmer than before .]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290873#Comment_290873 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290873#Comment_290873 Fri, 06 Aug 2021 22:00:11 +0100 fostertom https://www.glidevale.com/article/68/automatic-ventilation-from-glidevale-trickle-vents semi colon https://toma24.com/productcart/humidity-sensitive-trickle-vent-higroster stop new line
Don't know what they cost, never used em.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290906#Comment_290906 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290906#Comment_290906 Sun, 08 Aug 2021 15:06:05 +0100 minisaurus Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290916#Comment_290916 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290916#Comment_290916 Sun, 08 Aug 2021 22:00:50 +0100 Shevek
- Occupancy is currently 2 but could be 4 when rented out. Or 3 if we have a little one :confused:
- Volume is approx. 170 cu m
- Windows needed to be closed, at least at night, for 2-3 months if I recall correctly (lows and highs of 6º to 15º Dec to Feb)
- Washing is dried outside the envelope for most of the year, but in winter needs to be brought in at night to finish off.
- We do cook a lot but moisture hasn't been a problem, although that was probably because the laundry window next to the kitchen used to have a large vent grill at the top (because of the gas boiler). We removed that when we fitted new windows.

Thanks for the heads up on the trickle vents with humidity sensors Tom. Pretty cool how they work without electricity. No more expensive than acoustically attenuated vents too (€32 on that second link of yours). Is shutting off trickle vents based on humidity alone a good idea though? Could that lead to build up of CO2 in bedrooms over night?

An exhaust air heat pump is an option. Open to suggestions. I think from listening to MEP seminars I've also had it drummed into my head that MEV with trickle vents in this context will be the simplest, most cost-effective and healthy option. I've got to keep in mind that there's €2500 EU funding available for a heat pump system but not a ventilation system for whatever reason, but if I could combine the two then the funding is probably available for the heat pump element.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290917#Comment_290917 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290917#Comment_290917 Sun, 08 Aug 2021 22:02:43 +0100 Shevek Posted By: minisaurusAn EAHP could handle this and your heat question. I have a Bosch Compress
Is that a system with an external fan unit?]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290940#Comment_290940 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290940#Comment_290940 Mon, 09 Aug 2021 18:00:40 +0100 minisaurus Posted By: Shevek
Posted By: minisaurusAn EAHP could handle this and your heat question. I have a Bosch Compress

Is that a system with an external fan unit?

No, internal fan, and you can regulate the flow to suit.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290961#Comment_290961 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290961#Comment_290961 Tue, 10 Aug 2021 16:23:47 +0100 Shevek
But the second configuration? Exhaust air heat pump?

https://energie.pt/en/products/aquapura-monobloc]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290966#Comment_290966 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290966#Comment_290966 Tue, 10 Aug 2021 20:43:52 +0100 minisaurus Posted By: ShevekI was looking into this Aquapura Monobloc unit from Energie. The first configuration is air source heat pump.

But the second configuration? Exhaust air heat pump?


Could be EAHP - input air isn’t shown? You’d want some input air hole(s) somewhere.

Only does hot water, no radiators? Don’t forget that the “Nordic” EAHPs give you radiator and/or underfloor heating, as well as hot water :)

Why do you get wine bottles with the second configuration?]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290969#Comment_290969 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290969#Comment_290969 Tue, 10 Aug 2021 21:05:41 +0100 gravelld Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290976#Comment_290976 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290976#Comment_290976 Tue, 10 Aug 2021 22:10:36 +0100 djh Posted By: minisaurusWhy do you get wine bottles with the second configuration?
The label says it is also indoors, so presumably it's a chilled wine cellar. Well spotted!]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290986#Comment_290986 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290986#Comment_290986 Wed, 11 Aug 2021 12:19:36 +0100 Shevek
Exhaust air heat pump to heat water only and refresh air internally seems like a strange concept to me. Basically cooling your house down whenever you heat your water.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290987#Comment_290987 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=290987#Comment_290987 Wed, 11 Aug 2021 12:23:05 +0100 Shevek Posted By: gravelldI like Aereco's demand controlled units. If you're under 5m3/hm2 you'll need vents.
That an interesting company, thanks. They even have trickle vents designed for exactly where I was thinking of putting them:
https://www.aereco.com/products/air-inlets/eah2/]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291036#Comment_291036 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291036#Comment_291036 Thu, 12 Aug 2021 17:27:56 +0100 Shevek
I would typically close the windows when this happens to stop the damp coming inside, especially if it's also a cold morning. But trickle vents with humidity sensors are likely to just increase their aperture as the moisture laden air creeps inside.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291298#Comment_291298 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291298#Comment_291298 Fri, 27 Aug 2021 10:45:27 +0100 Shevek
Very often a fog rolls in off the Atlantic. Summer and winter (it’s foggy most mornings at the moment). In warm weather it can mean waking up sweaty but it dries up soon enough. In cold weather it’s really problematic and clearly contributes to a small mould problem in the flat (coupled with significant thermal bridges at the floor slabs).

The problem with the extract + trickle vent method is that this just pulls the fog inside (and at the moment just windows cracked open for ventilation, resulting in same problem). The only option being to get a separate dehumidifier.

So unless there are dehumidifying trickle vents out there we should be looking at a solution with integrated dehumidifier.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291303#Comment_291303 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291303#Comment_291303 Fri, 27 Aug 2021 12:49:38 +0100 djh

https://en.wikipedia.org/wiki/Fog_collection]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291308#Comment_291308 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291308#Comment_291308 Fri, 27 Aug 2021 19:22:06 +0100 Shevek Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291312#Comment_291312 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291312#Comment_291312 Fri, 27 Aug 2021 20:35:00 +0100 djh ]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291327#Comment_291327 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291327#Comment_291327 Sun, 29 Aug 2021 20:26:21 +0100 bxman Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291330#Comment_291330 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291330#Comment_291330 Sun, 29 Aug 2021 22:47:12 +0100 WillInAberdeen
Fortunately the foggy air isn't any wetter than normal, just colder, so it isn't bringing any extra moisture into the indoors. It is easily evaporated by warming up the air again by a few degrees above sea temperature, so once it's at indoor temperatures it doesn't make things damp. Is this what you are finding, or is it different that far south?

We used the radical solution of moving house a few miles inland, the haar rarely gets that far inland before evaporating.]]> Retrofitting continuous ventilation after fitting new windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291355#Comment_291355 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17140&Focus=291355#Comment_291355 Tue, 31 Aug 2021 18:08:29 +0100 Shevek Posted By: bxmanmaybe the mower is intelligent enough that you do not cut damp grass
ha, yes, cutting damp grass will clog up the mower!]]>