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Ventilation system advice needed


Foggy
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Hi, since we stopped using and closed off our open fireplace we have had issues with mould forming on walls, ceilings and around windows (mainly upstairs). I know we need to increase ventilation but I’m completely lost about the best way to do this.

 

Our house is a two story 1920s three bedroom semi that’s around 225 cubic meters . We have cavity wall insulation, loft insulation and double glazing along with non insulated suspended floors. Our heating is now gas central heating with rads and smart TRVs.

 

We do not have a bathroom vent at all but we do have an extractor for the kitchen. So I know some kind of vent is desperately needed in the bathroom. 

 

I don’t know if it’s worth us getting a heat recovery system given the age of the house but I also want something as eco friendly (and cheap to run) as possible. Especially with uncertainty energy costs in our futures. 

 

Given how many different options there are I’d love some advice so that I don’t get taken advantage of when I start getting quotes. 
 

So far I’ve looked into options including a standard bathroom extractor and a piv unit, dmev units, heat recovery dmev, a central heat recovery unit for the whole house or if just having vents for the upstairs would work as our loft is relatively open.
 

Money is very much an issue but I don’t want to go cheap on the installation and then be pumping hundreds in heat out of the house each year. 

 

I’ve gotten myself completely lost basically.

 

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18 minutes ago, Foggy said:

We have cavity wall insulation, loft insulation and double glazing along with non insulated suspended floors.

 

I don't wish to alarm but as soon as I see cavity wall insulation I get an uneasy feeling. What do you know about the type of fill you have and whether there are any known issues with it? And which walls have the mould - the party wall, just the outside walls, or what?

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Sounds very much like you have a ventilation issue.  I take you sleep with the windows and vent strip closed?  Without cross flow ventilation, your breath moisture is condensing on the cold areas around the windows.  Would also guess the CO reading in your bedrooms are very high, not good for your health.

 

Where you have mold clean off with a weak bleach solution.

 

Your closed off fire places should have a ventilator grid in them, this can be internal or external.

 

First things to do.

Do your windows have vent strips, if so  open them all, if you don't you will need to open the window slightly. 

 

You need extractors in your wet rooms, I would go with dMev, these are quite and run all the time, get ones with humidity detection so they boost only when needed, not every time you switch the light on or walk into the room. 

 

Or the other option would be dMVHR, but you need them installed in most room to be effective, quite like Prana units https://ecostream.org.uk/d-mvhr/

 

You can do all the above quite easily, mvhr will need you rip the house apart to install.

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1920 house should be leaky enough to have sufficient background ventilation. Please make sure you have not blocked any air brick vent for the suspended floor.

 

Forget heat recovery ventilation for a leaky house, no point and no payback. 

A simple WC extract fan would help your wetroom. Timer setting would be helpful. If using humidity sensor control type, make sure to tune down the set point otherwise you would have the fan running most of the time during cold winter (when RH is high indoor).

 

Open up trickle vent (windows vent strips).

 

Also please let us which wall you have condensation issue. 

Cavity insulation, if not installed properly, could mean bridging the DPC and cause damp at wall low level. 

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I don’t understand that, a leaky house is only leaky when it is windy or very windy.

 

A balanced heat recovery ventilation system will work 

 

relying on draughts for ventilation doesn’t work when it is calm and works progressively better til it becomes insanely wasteful as the wind speed increases

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10 minutes ago, tonyshouse said:

I don’t understand that, a leaky house is only leaky when it is windy or very windy.

 

A balanced heat recovery ventilation system will work 

 

relying on draughts for ventilation doesn’t work when it is calm and works progressively better til it becomes insanely wasteful as the wind speed increases

 

The time that you need "heat recovery" is when the outside temperature is low (e.g. below 10 degC). In such scenario the temperature difference between indoor and outdoor would be big enough that stack effect will come into play, particular in a leaky house, driving fresh cold air in and warm air at high level leak through the roof. the heat recovery system as such is not going to reduce your heating bill much.

 

 

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1 hour ago, Foggy said:

I’ve gotten myself completely lost basically.

Hi Foggy.

 

This is not uncommon, owning a house is a journey.

 

Often it's beneficial when you get stuck to go back to basics.

 

Start by going round the inside of the house and look at the openings.. doors and windows, wait for a windyish day and go round with the back or your hand feeling for drafts. If you have older double glazing you'll find a few. Often this is caused by the opening part of the window loosing it's shape as the glass holds the opening part square. What then happens is that the window does not shut right and make a tight seal on the gasket. Also the gaskets loose their flexibility so the locking mechanism has to work much harder to make a seal all round.

 

Pick a window and watch some videos on utube about how you adjust the window / door mechanisms. Have a go at it so the mechanism is working freely. Next look at the gaskets. There are load of different types but you can get sample kits to help you identify what gaskets you need.. see link below for idea.

 

https://www.handlesandhinges.co.uk/double-glazing-seal-gasket-sample-pack/

 

Now have a go at replacing the gaskets if need be, you are already on your way for little expense.

 

Next run you hand along the bottom of the skirting and find the drafts, note the position. At the same time see if there is mould at this level and note the position. Look up the walls in each room and note the position of any damp / mould. Next go into the attic and see how the insulation is laid, check to see it is not touching the underside of the roof / tiles and that the eaves are clear and the insulation is not clogging the eaves ventilation. Also look to see if you have downlighters in the ceiling that might be letting steam from say the shower into the attic.

 

The key in the attic is to look for places where you have moisture getting in and hitting a cold surface with no air flow. This applies elsewhere too.

 

Now go outside and look at where the outside walls are most exposed, check you gutters, down pipes and that the rainwater drains are running clear. Look under the floor and see if it is ventilated and that the air space is not full of rubbish. See how it all works.

 

Once you have got a handle on this then turn to your cavity wall insulation. Cavity walls in the 1920's were fairly new and the cavities we often smaller than they are today. The cavity wall insulation may be missing in places so look for odd mouldy spots in funny places, see if they marry up with the cold / exposed areas on the outside and ground levels that are say maybe higher and cooling the wall / stopping it breathing.

 

You need to be a bit of a detective and read/ learn a bit but once you get a feel for things you'll have a much better understanding on how your house is working fabric wise.

 

Next look at how you are living and using the house and identify the sources of moisture. Compare with your observations.

 

Once you have done this you'll be much more informed and thus able to target your spend most effectively and or make a small change to your living regime. It may be that by introducing ventilation in the right place, cutting out the drafts in the wrong place and adding the odd bit of insulation delivers the best return. Then if money to spare you can introduce more technology.

 

All the best.

 

 

 

 

 

 

 

Edited by Gus Potter
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13 hours ago, Radian said:

 

I don't wish to alarm but as soon as I see cavity wall insulation I get an uneasy feeling. What do you know about the type of fill you have and whether there are any known issues with it? And which walls have the mould - the party wall, just the outside walls, or what?


It’s not on exterior walls apart from in one bedroom along the very top corner where it meets the ceiling and the exterior bathroom wall. The latter is almost certainly because we don’t have a shower vent, the walls get wet in there when someone showers, even with the window open.

 

Other than those areas it’s mainly around and on windows, a couple of internal walls and some areas of ceiling. We have some curved corners on a couple of ceilings which are particularly bad, I know those can get missed with loft insulation so that’s another job I know we need to get done at some point. 
 

I forget to mention the relative humidity varies between 60% and 75% in the house.

 

13 hours ago, hb1982 said:

1920 house should be leaky enough to have sufficient background ventilation. Please make sure you have not blocked any air brick vent for the suspended floor.

 

Forget heat recovery ventilation for a leaky house, no point and no payback. 

A simple WC extract fan would help your wetroom. Timer setting would be helpful. If using humidity sensor control type, make sure to tune down the set point otherwise you would have the fan running most of the time during cold winter (when RH is high indoor).

 

Open up trickle vent (windows vent strips).

 

Also please let us which wall you have condensation issue. 

Cavity insulation, if not installed properly, could mean bridging the DPC and cause damp at wall low level. 


The cavity wall insulation was installed about 14 years ago and it’s only the last 2-3 years we have had a problem so I’m hoping that means it’s not causing the problem. The house was fine until we stopped using the open fire. My hypothesis is that open fires suck in a huge amount of air, heat it and then send it out of the chimney before writing us a bill for the fuel so it was acting as a negative pressure ventilation unit. That’s only my ponderings though. The chimney is capped properly with a small vent at the bottom and the top.

 

we don’t have any trickle vents, as far as I know the airbrick is not blocked but getting someone to check the ventilation under the floor is on my list.

 

 

12 hours ago, Gus Potter said:

Hi Foggy.

 

This is not uncommon, owning a house is a journey.

 

Often it's beneficial when you get stuck to go back to basics.

 

Start by going round the inside of the house and look at the openings.. doors and windows, wait for a windyish day and go round with the back or your hand feeling for drafts. If you have older double glazing you'll find a few. Often this is caused by the opening part of the window loosing it's shape as the glass holds the opening part square. What then happens is that the window does not shut right and make a tight seal on the gasket. Also the gaskets loose their flexibility so the locking mechanism has to work much harder to make a seal all round.

 

Pick a window and watch some videos on utube about how you adjust the window / door mechanisms. Have a go at it so the mechanism is working freely. Next look at the gaskets. There are load of different types but you can get sample kits to help you identify what gaskets you need.. see link below for idea.

 

https://www.handlesandhinges.co.uk/double-glazing-seal-gasket-sample-pack/

 

Now have a go at replacing the gaskets if need be, you are already on your way for little expense.

 

Next run you hand along the bottom of the skirting and find the drafts, note the position. At the same time see if there is mould at this level and note the position. Look up the walls in each room and note the position of any damp / mould. Next go into the attic and see how the insulation is laid, check to see it is not touching the underside of the roof / tiles and that the eaves are clear and the insulation is not clogging the eaves ventilation. Also look to see if you have downlighters in the ceiling that might be letting steam from say the shower into the attic.

 

The key in the attic is to look for places where you have moisture getting in and hitting a cold surface with no air flow. This applies elsewhere too.

 

Now go outside and look at where the outside walls are most exposed, check you gutters, down pipes and that the rainwater drains are running clear. Look under the floor and see if it is ventilated and that the air space is not full of rubbish. See how it all works.

 

Once you have got a handle on this then turn to your cavity wall insulation. Cavity walls in the 1920's were fairly new and the cavities we often smaller than they are today. The cavity wall insulation may be missing in places so look for odd mouldy spots in funny places, see if they marry up with the cold / exposed areas on the outside and ground levels that are say maybe higher and cooling the wall / stopping it breathing.

 

You need to be a bit of a detective and read/ learn a bit but once you get a feel for things you'll have a much better understanding on how your house is working fabric wise.

 

Next look at how you are living and using the house and identify the sources of moisture. Compare with your observations.

 

Once you have done this you'll be much more informed and thus able to target your spend most effectively and or make a small change to your living regime. It may be that by introducing ventilation in the right place, cutting out the drafts in the wrong place and adding the odd bit of insulation delivers the best return. Then if money to spare you can introduce more technology.

 

All the best.

 

 

 

 

 

 

 


Thank you for that, that’s really helpful.

 

we are currently waiting to get most of our double glazing replaced because we have some issues with the current units. My worry was that the new UPVC will just make the mould issue worse due to the house becoming less leaky.

 

I’ve been wondering about buying a thermal camera to check for missing spots of insulation as they aren’t too expensive, perhaps that should be something I do this winter.

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13 hours ago, hb1982 said:

 

The time that you need "heat recovery" is when the outside temperature is low (e.g. below 10 degC). In such scenario the temperature difference between indoor and outdoor would be big enough that stack effect will come into play, particular in a leaky house, driving fresh cold air in and warm air at high level leak through the roof. the heat recovery system as such is not going to reduce your heating bill much.

 

 


So that basically means heat recovery is a waste of money in the U.K. unless the house has very low air permeability? 

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4 minutes ago, Foggy said:


So that basically means heat recovery is a waste of money in the U.K. unless the house has very low air permeability? 

I don't agree.

 

The alternative is no ventilation and trust to natural leaks in the building which is usually poor and unreliable.  Or mechanical extraction that draws COLD air in to replace the heat you are expelling from the building and in 99% of cases allows cold air to blow IN when the fan is not on.

 

Of course mvhr works better in an air tight building but I bet it would still be of benefit in a less than perfect building.

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So if it's not windy, you don't have trickle vents - you don't have ventilation.

 

Back to basic - open the windows, get a fan in the bathrooms.

 

The average person looses between half to one litre of water per day just by breathing.  If you don't ventilate you end up with damp house - you have a damp house.

 

Your problem was being masked by open fireplaces.

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Just now, JohnMo said:

So if it's not windy, you don't have trickle vents - you don't have ventilation.

 

Back to basic - open the windows, get a fan in the bathrooms.

 

The average person looses between half to one litre of water per day just by breathing.  If you don't ventilate you end up with damp house - you have a damp house.

 

Your problem was being masked by open fireplaces.


Certainly, we do try to open windows a crack when we can but it’s not enough. I didn’t want to waste money getting a bathroom vent installed if a central unit was going to be a better long term solution. It seems like a bathroom extractor is the first thing to do though along with other insulation problem solving.

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dMVHR is what I would be going for unless you plan to do major refurb - run ducting between floor levels, air seal all rooms etc. Regarding the room with damp at the top of the ceiling, it may be that the cavity fill has settled a bit there. Is the top of the cavity exposed to the loft such as you could get an inspection camera in to find out? You can pick up an Inspection Camera for peanuts and it would help in numerous investigations. If you fancy a thermal camera and have the money for it, then yes they're great. I've had loads of use out of mine but I do use it for electronics development.

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1 hour ago, Radian said:

dMVHR is what I would be going for unless you plan to do major refurb - run ducting between floor levels, air seal all rooms etc. Regarding the room with damp at the top of the ceiling, it may be that the cavity fill has settled a bit there. Is the top of the cavity exposed to the loft such as you could get an inspection camera in to find out? You can pick up an Inspection Camera for peanuts and it would help in numerous investigations. If you fancy a thermal camera and have the money for it, then yes they're great. I've had loads of use out of mine but I do use it for electronics development.


I actually went ahead and got a thermal camera on Amazon. I figure I can sell it after I’m done and recoup some of the cost. I’ve often wondered if there’s any gaps in the cavity insulation so I can give the house a good look over now and see what needs doing. 
 

dmvhr is appealing, especially as I can spread the cost by doing one at a time. 

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1 minute ago, Foggy said:

I actually went ahead and got a thermal camera on Amazon.

 

 Cool. Looking forward to some piccies ? Now get a bullet camera and poke that into the cavity for a more detailed examination ?

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4 minutes ago, Radian said:

 

 Cool. Looking forward to some piccies ? Now get a bullet camera and poke that into the cavity for a more detailed examination ?


This is going to get expensive! It would be good to look under the floors though…..

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22 hours ago, ProDave said:

I don't agree.

 

The alternative is no ventilation and trust to natural leaks in the building which is usually poor and unreliable.  Or mechanical extraction that draws COLD air in to replace the heat you are expelling from the building and in 99% of cases allows cold air to blow IN when the fan is not on.

 

Of course mvhr works better in an air tight building but I bet it would still be of benefit in a less than perfect building.

 

I should say

Heat Recovery is good and should be considered

Benefit of heat recovery ventilation would subject to the house air tightness

It is an expensive investment. If money is tight, it may not be the best use of money.

 

For a house without continuous extraction (MEV) or MVHR, trickle vent should be opened / manually adjusted to maintain sufficient background ventilation. A trial and trusted method although not the most energy efficient. 

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Thank you for the input everyone. I think I will try to get dmvhr units installed starting with the bathroom. The information here has been really useful and made me feel  a lot more confident dealing with companies when I start getting quotes.

 

 

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Good good. Maybe get a £5 humidistat to get some before and after RH readings.

 

I installed a central. MEV in my parents loft in their uninsulated house. It has reduced the damp in the house for sure. 

 

Any chance you’d share some of the thermal pics. I’m interested in purchasing one, 

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