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ThunderGuts |
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ThunderGuts World Chat Champion
Joined: 13 Nov 2018 Karma :
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Posted: 16:46 - 17 Nov 2021 Post subject: Positive pressure ventilation |
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As the knowledge bounds of the BCF populace seem limitless, I'll throw this one in here to see what people's thoughts are.
We have a fairly common issue in that a period house has double glazing (with no trickle vents) so therefore is pretty well sealed, it's not practical (for security reasons) to have the windows either open or on "vent/night mode" 24/7. As a result, we get issues, particularly on the north side of the house and downstairs (where it's coolest) with high humidity, resulting in a bit of mould in corners, on the back of the sofa etc..
We have experimented with dehumidifiers and they do draw out plenty of moisture, but they're also noisy, require emptying fairly frequently and I suspect draw a noticeable collective power drain when ran as a permanent solution.
So my thoughts at present for a relatively economical but hopefully effective solution is to get trickle vents installed retrospectively, then get a positive pressure ventilation system installed in the loft (I saw installed, I think it's a DIY job as it looks very simple). The theory is they draw cool air from the loft void (ours is "roughly" converted, but still a hatch-access area and isn't sealed from the outside very well, so should be no issue in getting outside air and if necessary I could locate the unit behind the stud walls), this air is then pumped into the house where it warms up, it's relative humidity drops and at the same time the increased pressure in the house encourages a gradual flow of air out of the trickle vents (and any other openings in the building fabric). Yes, there's an overhead with heating as there's some cool air which will need warming, but it's better than having mouldy walls.
Has anyone experience of these positive pressure ventilation systems?
Cheers. ____________________ TG. |
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steve the grease |
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steve the grease Crazy Courier
Joined: 26 Jan 2018 Karma :
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Posted: 17:09 - 17 Nov 2021 Post subject: |
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We have 2 fires- ( a Rayburn and a woodburner) , by September when we havent had a fire for months it starts to get difficult to close the internal doors because of the damp.
Ignoring the heat, the fires pull quite a lot of air through the house (before venting it up the chimneys of course) and dry the whole house out a treat . Positive ventilation sounds like a great idea and would do a similar job - moving air through the house, in a different way of course, but would cost a lot less than de- humidifiers would do, they can be expensive to run, and only affect one room rather than the whole house. ____________________ All the above is my personal opinion, you can see my lips move, but I'm talking out of my arse.
I've been riding, and fixing , bikes for 50 years, in that time the more I learn, the less I am absolutely sure of..... |
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tatters |
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tatters Exxon Valdez
Joined: 05 Jan 2004 Karma :
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Posted: 17:18 - 17 Nov 2021 Post subject: |
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A older house even with double glazing will not be very well sealed therefore the additional of a HRV (heat recovery ventilator) which can also dehumidify would not be ideal, you would also have to run ductwork and can not vent into or from an loft/attic space. There are ductless options such as below but they are designed for single zones.
https://foursevenfive.com/lunos-e/
For low cost dehumidification/air exchange the installation of a 150-200 cfm thru-wall exhaust fan controlled by a humidistat would work. With the house not being as airtight as a modern build this shouldn't created noticeable negative static pressure when it is running. ____________________ Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650 Present:G650XC,C12,KZ750,1190ADV |
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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Posted: 17:41 - 17 Nov 2021 Post subject: |
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High ceilings? Sometimes even a ceiling fan on low can move the hot air back down in larger living rooms.
Humidity in my house reduced massively after I fitted a proper, externally vented cooker hood.
Also worth making sure you don't have a leak somewhere under the floor. Lift a couple of boards and stick your head in and have a sniff and a good look with a torch. Mould on the back of the sofa sounds like a bit more that just condensation. That would tend to form on a cold surface when the surface temperature reaches the dew point. If you have any sort of wall insulation, I wouldn't expect the walls to get that cold. I get that in my porch but I grow plants in there and it's only a single skin of blocks. I put up insulated wallpaper in there which helped reduce condensation by keeping the surface temperature higher.
Mrs stinkwheel lived in a house at her last work that was chronically damp. A few years later we found out there had been a burst water pipe under the house and it was effectively sitting on top of a swamp. They had to take up the floor and dig a hole in the soil under the house which kept filling with water which they then pumped out. Took weeks to dry it all out. ____________________ “Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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ThunderGuts |
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ThunderGuts World Chat Champion
Joined: 13 Nov 2018 Karma :
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Posted: 17:44 - 17 Nov 2021 Post subject: |
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steve the grease wrote: | We have 2 fires- ( a Rayburn and a woodburner) , by September when we havent had a fire for months it starts to get difficult to close the internal doors because of the damp.
Ignoring the heat, the fires pull quite a lot of air through the house (before venting it up the chimneys of course) and dry the whole house out a treat . Positive ventilation sounds like a great idea and would do a similar job - moving air through the house, in a different way of course, but would cost a lot less than de- humidifiers would do, they can be expensive to run, and only affect one room rather than the whole house. |
We have a woodburner in the living room, but in practice it isn't lit that frequently or for long enough to be a real benefit (if we worked from home it might be a different story of course).
tatters wrote: | A older house even with double glazing will not be very well sealed therefore the additional of a HRV (heat recovery ventilator) which can also dehumidify would not be ideal, you would also have to run ductwork and can not vent into or from an loft/attic space. There are ductless options such as below but they are designed for single zones.
https://foursevenfive.com/lunos-e/
For low cost dehumidification/air exchange the installation of a 150-200 cfm thru-wall exhaust fan controlled by a humidistat would work. With the house not being as airtight as a modern build this shouldn't created noticeable negative static pressure when it is running. |
The type I'm thinking of doesn't operate heat recovery, instead it literally just pumps air into the house from the roof void. It is intended to just generally (slightly) pressurise in the inside of the house, creating a flow of air from the input of the positive ventilation fan out to the trickle vents and any other gaps in the building fabric. ____________________ TG. |
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ThunderGuts |
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ThunderGuts World Chat Champion
Joined: 13 Nov 2018 Karma :
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Posted: 17:55 - 17 Nov 2021 Post subject: |
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stinkwheel wrote: | High ceilings? Sometimes even a ceiling fan on low can move the hot air back down in larger living rooms.
Humidity in my house reduced massively after I fitted a proper, externally vented cooker hood.
Also worth making sure you don't have a leak somewhere under the floor. Lift a couple of boards and stick your head in and have a sniff and a good look with a torch. Mould on the back of the sofa sounds like a bit more that just condensation. That would tend to form on a cold surface when the surface temperature reaches the dew point. If you have any sort of wall insulation, I wouldn't expect the walls to get that cold. I get that in my porch but I grow plants in there and it's only a single skin of blocks. I put up insulated wallpaper in there which helped reduce condensation by keeping the surface temperature higher.
Mrs stinkwheel lived in a house at her last work that was chronically damp. A few years later we found out there had been a burst water pipe under the house and it was effectively sitting on top of a swamp. They had to take up the floor and dig a hole in the soil under the house which kept filling with water which they then pumped out. Took weeks to dry it all out. |
So, yes we do have high ceilings (circa 10ft downstairs). One of the first things I did when I got the house was fit an externally vented cooker hood, so that's ticked too.
In terms of damp underneath, well yes there is an issue there (as you may or may not recall from a post a few years ago). Unfortunately, no easy fix for that one - high water table means there's often standing water under the house but I have explored many options to deal with this and haven't arrived at a suitable solution; there are three "solutions";
1) Simplest, dig a pit, fit a sump pump and backfill with gravel. There are issues with the water table being lowered locally (which can upset the foundations as the house is sitting on clay) but the bigger issue is there's going to be a flow of water through the brick footings into the void, eroding both the lime mortar and potentially the soil too
2) Tank the floor void; line the void floor with concrete, tank the walls and floor and have a sump pump. Definitely the best for humidity control, but again concerns over the water table and erosion
3) French drains (deep ones!) around the perimeter of the house; partial effectiveness unless the neighbour agrees their house is included in the scheme. Massive upheaval and still the issues with changed ground conditions for the foundations
Essentially, all of these have risks which are significant, albeit ones which might not manifest themselves (either in the short term or possibly ever). The thing is, if they do manifest themselves, we're talking structural movement . . . not good. Options 2 and 3 are properly expensive too.
My plan with the floor void is to increase the ventilation with a combination of upgraded existing airbricks and some new ones. ____________________ TG. |
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Kawasaki Jimbo |
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Kawasaki Jimbo World Chat Champion
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JackButler |
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JackButler Traffic Copper
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ThunderGuts |
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ThunderGuts World Chat Champion
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ThunderGuts |
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ThunderGuts World Chat Champion
Joined: 13 Nov 2018 Karma :
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Posted: 10:13 - 18 Nov 2021 Post subject: |
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Edit: little diagram; essentially my idea is there should be a slight movement of air from the house into the floor void in addition to out through the trickle vents, but then good airbrick ventilation to the floor void. This should prevent moist air moving from the void into the house, but also allow the void to be well ventilated.
Edit edit: sorry if stating the obvious, but R/H is relative humidity
https://www.bikechatforums.com/files/ppv.jpg ____________________ TG. |
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A100man |
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A100man World Chat Champion
Joined: 19 Aug 2013 Karma :
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Posted: 13:47 - 19 Nov 2021 Post subject: |
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You say period house but how old?
Has the DPC failed or been breached somehow causing damp to enter the house form the ground? I assume all rainwater goods are in sound working condition
I've not heard of venting a house in this way. I mean trying to force enough damp air through tiny trickle vents seems implausible. More (under floor) vents/airbricks - yes and also extractor fan in damp room, but I think if possible try and address the cause. ____________________ Now: A100, GT250A, XJ598, FZ750
Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600 |
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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Posted: 19:19 - 19 Nov 2021 Post subject: |
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My worry would be that the air will take the path of least resistance. So it'll come down out of the attic then make a bee-line for the nearest vent.
So I'd imagine you'll get a cold draught upstairs and slamming doors into the stairwell. Because how is it going to get through the floor to move this air downstairs? The floors in my house are pretty much draught-proof because they have carpet and underlay on top and plaster underneath.
That said, maybe it does work, I do know I wouldn't want to leave my loft hatch open! It's bloody freezing cold in there in the winter, and draughty. As it should be with a cold roof.
Any reason you couldn't fit a radiator behind the sofa against the North wall? ____________________ “Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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F18 |
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F18 Renault 5 Driver
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stinkwheel |
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stinkwheel Bovine Proctologist
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DJS |
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DJS Nitrous Nuisance
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kramdra World Chat Champion
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ThunderGuts |
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ThunderGuts World Chat Champion
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Posted: 10:28 - 24 Nov 2021 Post subject: |
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Thanks all for the responses.
Will have to investigate the heated options. ____________________ TG. |
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ThunderGuts |
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ThunderGuts World Chat Champion
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defblade |
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defblade World Chat Champion
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Posted: 01:38 - 25 Nov 2021 Post subject: |
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Drimaster is bloody brilliant.
Wife insisted we bought the heater extra part the first winter, but I wouldn't have bothered.
Seems kinda pricey for what is effectively a large fan with filters, but it works so well you have to forgive it.
Feels (on the landing near the vent) sort of like you've got a window open somewhere.
Yes, very easy DIY fit, so long as you can get electric into the loft.
Early 1700's stone house here, no more streaming windows since 2 days after fitting the PIV - maybe 8 or 10 years ago now. ____________________ Honda Varadero 125cc => Suzuki Bandit 650 33bhp => 77bhp =>
BMW K1200R Sport 163bhp => Aprilia Shiver GT 750 95bhp |
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Ribenapigeon |
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Ribenapigeon Super Spammer
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Old Thread Alert!
The last post was made 2 years, 117 days ago. Instead of replying here, would creating a new thread be more useful? |
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