Tue, 06 Oct 2026 02:15:59 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307283#Comment_307283 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307283#Comment_307283 Sat, 23 Nov 2024 11:00:41 +0000 daveking66
My sister in laws house (old, poorly insulated and single glazed) suffers from condensation and is considering installing PIV. From what I’ve read on other posts it seems that a dehumidifier, or two, might be a better option. Any comments or considerations?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307284#Comment_307284 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307284#Comment_307284 Sat, 23 Nov 2024 12:38:35 +0000 djh
Dehumidifiers might work. I don't know anything about their costs or effectiveness. Somebody else will have to comment.

One thing I know works is increasing the ventilation. When we lived for a while in an old damp house we opened the windows wide even in winter for a while every day. That added to the heating bill of course. But heating bills are bad anyway in old, poorly insulated, single glazed buildings.

The windows can be improved fairly cheaply by adding secondary glazing, and/or shutters at night.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307285#Comment_307285 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307285#Comment_307285 Sat, 23 Nov 2024 16:14:41 +0000 Mike1
I've only used a dehumidifier to help dry out new construction, but I'd say it was worth trying a well-rated inexpensive one from Amazon /elsewhere.

If kitchen & bathroom extractor fans aren't already fitted, I'd add them; if they are present then upgrade at least the bathroom one with a humidistat. The next step up would be dMVHR (decentralised mechanical ventilation with heat recovery), but then the costs start mounting so a good idea to consider it (and alternatives) as part of a plan to upgrade the whole house. In connection with that, keep a look out in case any useful grants / loans emerge from the Government's upcoming Warm Homes Plan - details expected next year.

Also worth thinking about what can be done to reduce the production of moisture. In particular not cooking with open pans, not drying washing indoors, and running the cold water into the bath before adding the hot.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307286#Comment_307286 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307286#Comment_307286 Sat, 23 Nov 2024 16:48:16 +0000 djh Posted By: Mike1running the cold water into the bath before adding the hotOn that topic, it's surprising how good oil is at reducing evaporation. Because oil floats on the surface.

A shower uses a whole lot less water than a bath of course!]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307287#Comment_307287 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307287#Comment_307287 Sun, 24 Nov 2024 08:38:37 +0000 Cliff Pope
That depends how long a shower you take. A quick one just to wash off dirt, obviously - just in and out, about a minute. But if you have a long hot luxurious shower it can use as much water as a bath.
I tried an experiment once by leaving the plug in the bath while having a shower. 5 minutes and I had a bathfull.

Also a shower is perfect for producing as much steam as possible - ypou couldn't really improve on a device that trickles hot water from a height:) So you need a powerful extractor as close to the shower as possible, which is chilly when you get out.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307288#Comment_307288 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307288#Comment_307288 Sun, 24 Nov 2024 09:59:27 +0000 Jonti On the OPs original topic, I would suggest buying a dehumidifier and using it in one room which is effected by humidity to see how it works.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307289#Comment_307289 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307289#Comment_307289 Sun, 24 Nov 2024 12:01:27 +0000 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307290#Comment_307290 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307290#Comment_307290 Sun, 24 Nov 2024 12:40:57 +0000 Kenny_M
In a room which has high humidity and if you have electric heating, a dehumidifier is more energy efficient than heating and ventilating, because at all of the energy being used by the dehumidifier is converted to heat so it is at least as energy efficient has an electric heater, and if you don't then need to ventilate you are not losing any heat to the outside. In fact I believe a dehumidifier is more energy efficient than an electric heater because of the latent heat effect from the desiccant. If your heating is of a cheaper type, such as GCH, then the dehumidifier will be more expensive to run, but probably not much if you take into account the fact that you are not losing any heat by ventilating.

If its just condensation on single glazed windows there might not actually be a humidity problem. If its cold enough outside you will still get condensation on windows with normal indoor RH. Those window vac cleaners are good for condensation on window panes.

Edit: corrected to 'domestic use' in first line, not 'indoor use'. Would have to be some dehumidifier for outdoor use! :)]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307292#Comment_307292 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307292#Comment_307292 Mon, 25 Nov 2024 08:17:16 +0000 revor https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307321#Comment_307321 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307321#Comment_307321 Wed, 27 Nov 2024 13:43:00 +0000 gravelld
Precisely the reason I opted against it too. Installed a dcMEV instead - Aereco. It means you have to run some ducting, but I think it's safer long term and you don't necessarily have to run it _everywhere_.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307326#Comment_307326 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307326#Comment_307326 Wed, 27 Nov 2024 16:51:09 +0000 fostertom
What are you doing about inlet? I like the idea of trickle-vent type inlets in every room, controlled by inbuilt mechanical humidity sensor. So in any one room, rising humidity opens the trickle vent - only high-CO2 rooms get full ventilation. That much seems established, but I'd a thought that the fan should also detect the pressure differential across itself and throttle back when that differential increases, as it does when more inlets are closed. Was that part of your scheme?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307328#Comment_307328 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307328#Comment_307328 Wed, 27 Nov 2024 18:16:10 +0000 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307329#Comment_307329 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307329#Comment_307329 Wed, 27 Nov 2024 20:45:45 +0000 djh Posted By: fostertomI'm interested in those, since i heard vent guru Peter Rickaby prefer MEV to MHVR, for simplicity, and lower elect consumption which partly compensates for the lack of the (small) energy saving by recovery.I worked out the numbers for my house recently as it happens.

The power required if I had to heat my ventilation air from freezing to 20°C (which is admittedly a slightly worse case than reality at the mo) is about 830 W (just under 3 kWh per day). My MVHR recovers about 700 W of that, at a running cost of 29 W IIRC (0.7 kWh per day).

So if you have a reference of Rickaby spouting some contrary nonsense, I'd appreciate a link.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307331#Comment_307331 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307331#Comment_307331 Wed, 27 Nov 2024 23:07:22 +0000 fostertom http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9383&page=1 - what debates we had back then!]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307332#Comment_307332 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307332#Comment_307332 Wed, 27 Nov 2024 23:09:31 +0000 fostertom Posted By: tonyI hate trickle ventilators with a vengeanceMe too, but the hummidity-controlled (proxy for CO2) ones cost more than peanuts and seal tight(er) when closed.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307333#Comment_307333 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307333#Comment_307333 Thu, 28 Nov 2024 08:08:43 +0000 PeterStarck Posted By: gravelld> The problem is that it supplies fresh filtered air, yes, but where does the humid stale air go?

Precisely the reason I opted against it too. Installed a dcMEV instead - Aereco. It means you have to run some ducting, but I think it's safer long term and you don't necessarily have to run it _everywhere_.

I will be using PIV and will be extracting from the bathrooms and kitchen using a continuous running fan.

https://www.epicair.co.uk/products/greenwood-unity-cv2gip-dmev-fan

Min 1.1W to Max 4.1W shouldn't be too bad.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307334#Comment_307334 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307334#Comment_307334 Thu, 28 Nov 2024 08:14:58 +0000 Victorianeco
Thanks]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307335#Comment_307335 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307335#Comment_307335 Thu, 28 Nov 2024 08:17:56 +0000 Victorianeco https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307336#Comment_307336 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307336#Comment_307336 Thu, 28 Nov 2024 08:32:56 +0000 fostertom https://www.bpdstore.co.uk/glidevale-energy-saver-humidity-sensitive-trickle-ventilator/p/182 and many others]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307342#Comment_307342 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307342#Comment_307342 Thu, 28 Nov 2024 21:49:23 +0000 Victorianeco
Or just fit a MVHR unit and skip all these extra air leakage points?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307343#Comment_307343 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307343#Comment_307343 Thu, 28 Nov 2024 23:39:47 +0000 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307344#Comment_307344 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307344#Comment_307344 Fri, 29 Nov 2024 09:36:39 +0000 Doubting_Thomas
https://www.passivhaustrust.org.uk/UserFiles/File/research%20papers/MVHR/2020.04.27-The%20Case%20for%20MVHR-v7%20new%20cover.pdf]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307351#Comment_307351 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307351#Comment_307351 Fri, 29 Nov 2024 13:10:28 +0000 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307352#Comment_307352 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307352#Comment_307352 Fri, 29 Nov 2024 13:23:24 +0000 Doubting_Thomas Posted By: fostertomAt a quick look, the report only really compares MVHR with 'natural' ventilation, hardly with MEV, PIV or other alternatives.

There's a paragraph and table on page 3 which compares Nat Vent, MVHR & MEV

"Mechanical Extract Ventilation (MEV), whilst able to provide a good level of fresh air, draws this air from the outside, through gaps in the fabric and trickle vents. Thus, the air is not filtered, and external pollutants are actually sucked into the building. There is also no real control over where air enters the building, so good levels of air exchange cannot be guaranteed in all rooms or areas. The stack effect means that vents or open windows in upstairs bedrooms may become an exhaust route for stale air rather than inlets for fresh."

and more on page 8:

"Lowe concludes that MEV ventilation will result in lower emissions than MVHR systems of intermediate levels of performance at air permeabilities of greater than 3 m³/m².hr. However, he also notes that MVHR equipment which is ‘efficient by current standards’ is likely to outperform MEV at all levels of air permeability.

Lowe also notes that dwellings using natural ventilation with an air permeability of less than 8 m³/m².hr are almost certainly likely to lead to underventilation as occupants will not open windows and, as a result he does not evaluate the relative performance of natural ventilation below 5 m³/m².hour in comparison to MVHR or MEV. In effect, he considers that natural ventilation is inappropriate below 5 m³/m².hour."]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307353#Comment_307353 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307353#Comment_307353 Fri, 29 Nov 2024 15:11:38 +0000 fostertom
BTW I think the report exagerates MEV's 'no real control over where air enters the building' as it doesn't consider an MEV where inlet to each room is opened or closed by humidistat. System 'suction' would be such that flow is significant when a room's humidistat is open, relatively much less (by leakage) when it's closed - and system 'suction' would ramp down when total inlet resistance goes higher as inlets close.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307354#Comment_307354 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307354#Comment_307354 Fri, 29 Nov 2024 15:19:30 +0000 djh https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307355#Comment_307355 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307355#Comment_307355 Fri, 29 Nov 2024 17:25:47 +0000 fostertom
If the house were perfectly airtight, and all humidistat-controlled inlets closed, so no flow in the ductwork, the fan would throttle back to almost nothing, just a nominal suction so when an inlet opened, some flow would start, while pressure differential across the fan would drop and it would ramp up to maintain the differential. Flow (and electricity consumption) would be proportional to the number of room calling for ventilation, and to what degree. A minimum differential could be set, so a minimum vent rate (thro leakage) would be maintained 24/7.

The other feature advocated - the humidistat-controlled inlets - is not a fan function, is readily available.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307356#Comment_307356 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307356#Comment_307356 Fri, 29 Nov 2024 17:28:27 +0000 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307357#Comment_307357 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307357#Comment_307357 Fri, 29 Nov 2024 18:16:29 +0000 gravelld Posted By: fostertom
What are you doing about inlet? I like the idea of trickle-vent type inlets in every room, controlled by inbuilt mechanical humidity sensor. So in any one room, rising humidity opens the trickle vent - only high-CO2 rooms get full ventilation. That much seems established, but I'd a thought that the fan should also detect the pressure differential across itself and throttle back when that differential increases, as it does when more inlets are closed. Was that part of your scheme?That implies a constant draw from the unit. Mine works in a different way; once any of the outlets detects high humidity, or in the case of the wet rooms movement, the outlets open wider. This allows the unit to draw more air.

The 'inlet' is therefore the building fabric. Obviously I'd like an airtight home, but there was no financially practical way to achieving one. I prefer drawing colder air into the house than pushing warmer air out of the house, due to the concern about interstitial condensation.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307358#Comment_307358 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18242&Focus=307358#Comment_307358 Fri, 29 Nov 2024 18:17:33 +0000 gravelld Posted By: Victorianeco@Gravelld Where did you buy your unit from and what is your experience and current setup?Direct from Aereco. They were extremely good with support - although it didn't really need much handholding.]]>