Dealing with condensation…

[HughF]

Background; 1946 end of terrace, block, filled cavity (2”) 300mm loft insulation, double glazing… two persons, 5 cats, gas central heating, flow temp is around 55.

 

I don’t know what the indoor air quality is like but it’s probably poor (I don’t live here at present, just visit occasionally).

 

Anyway, would I need a full Mvhr retrofit deal with the causes of this, or could I get away with just a couple of dMVHR through the wall upstairs. Leaving a window cracked open isn’t an option.

 

*yes, I spent an hour yesterday washing and de-moulding all the windows, and then had a rant at my wife for letting it get this bad - it’s her place.

[jayc89]

Anecdotally I've heard PIV works wonders for this type of problem. It's certainly a quicker and easier fix than MVHR. 

[Conor]

Are there trickle vents in 5h3 windows? I'm assuming not. We lived in an apartment like this, got the landlord to replace the three knackered extractor fans, and I left a couple of windows open on the second position and issues went away.

[HughF]

 No trickle vents (2012 windows), exposed location. The house is warm but stuffy. Getting the windows left open isn’t going to happen. I would need a fit and forget heat recovery solution really.
 

No extractor fans anywhere… 

 

It really needs a deep renovation but I don’t have anywhere to house the occupants whilst doing the work. Original heating and wiring from ‘86, one double socket in each room.

 

We’re going out the back this year which will give us a bit of space to put the occupants in and do one room at a time.

[Roundtuit]

Unless you can make it airtight, I would think hard before embarking on the mvhr route.  I'd invest in a decent dehumidifier or two and try that; we ran a cheap one (£100?) 24-7 in our last place over the winter months and it made a massive improvement condensation levels.

Edited January 22, 2023 by Roundtuit
typo

[JohnMo]

54 minutes ago, HughF said:

No trickle vents

 

54 minutes ago, HughF said:

No extractor fans

Think you have answered your own cause.

 

Best two fixes are PIV or MEV. PIV, one central unit in loft or elsewhere, one supply outlet. MEV, centralised extract unit taking air from all wet rooms, can get them so they only when required and close down or open extract points as needed.

 

PIV is either on or off, MEV, ventilation only as required, if specified correctly.  

 

You can retrofit trickle vents, or vents in the walls of dry rooms, but get them so they auto open and close based on humidity.  

 

MVHR without airtightness is a waste of money.

[nod]

50 minutes ago, Roundtuit said:

Unless you can make it airtight, I would think hard before embarking on the mvhr route.  I'd invest in a decent dehumidifier or two and try that; we ran a cheap one (£100?) 24-7 in our last place over the winter months and it made a massive improvement condensation levels.

Plus 1 

Weve a couple of our rentals that suffer this 

I’ve added bathroom fans and vents 

Supplying two dehumidifiers in each works well Cheap to buy and run 

[ProDave]

46 minutes ago, Roundtuit said:

Unless you can make it airtight, I would think hard before embarking on the mvhr route.  I'd invest in a decent dehumidifier or two and try that; we ran a cheap one (£100?) 24-7 in our last place over the winter months and it made a massive improvement condensation levels.

Why do you say that?

 

The house clearly has poor air quality, insufficient ventilation at the moment.  So some improvement is necessary.

 

Dehumidifiers will remove most of the excess moisture so will cure the most noticable issue, the condensation, at the expense of needing electricity to power them and generally being noisy irritating things.

 

But that does not cure the poor air quality.  for that you need proper ventilation.

 

I keep seeing people recommend DMEV or PIV for this, but all that does is blow in fresh cold air or suck out stale air with the same amount of cold air being sucked in any way it can.  Neither have heat recovery so while they will improve the air quality, they will cool the house / increase heating required.

 

Yes for sure for best results you want an air tight house.  But I don't understand the logic of saying mvhr is a waste of time if the house is not air tight.  If you do fit mvhr to a leaky house, at least some of your ventilation will benefit from the heat recovery.  Balance the system properly so you are not pressurising or depressurising the house and little else will enter or exit through all the leaks except perhaps on a windy day.  

 

I would certainly say if you get the chance go ahead with mvhr.

 

Since I appear to be in the minority here, I await incoming.

[MikeGrahamT21]

11 minutes ago, ProDave said:

Why do you say that?

 

The house clearly has poor air quality, insufficient ventilation at the moment.  So some improvement is necessary.

 

Dehumidifiers will remove most of the excess moisture so will cure the most noticable issue, the condensation, at the expense of needing electricity to power them and generally being noisy irritating things.

 

But that does not cure the poor air quality.  for that you need proper ventilation.

 

I keep seeing people recommend DMEV or PIV for this, but all that does is blow in fresh cold air or suck out stale air with the same amount of cold air being sucked in any way it can.  Neither have heat recovery so while they will improve the air quality, they will cool the house / increase heating required.

 

Yes for sure for best results you want an air tight house.  But I don't understand the logic of saying mvhr is a waste of time if the house is not air tight.  If you do fit mvhr to a leaky house, at least some of your ventilation will benefit from the heat recovery.  Balance the system properly so you are not pressurising or depressurising the house and little else will enter or exit through all the leaks except perhaps on a windy day.  

 

I would certainly say if you get the chance go ahead with mvhr.

 

Since I appear to be in the minority here, I await incoming.

im with you @ProDave having installed MVHR in a very leaky house, still the best money I’ve spent so far

[jayc89]

17 minutes ago, ProDave said:

Why do you say that?

 

The house clearly has poor air quality, insufficient ventilation at the moment.  So some improvement is necessary.

 

Dehumidifiers will remove most of the excess moisture so will cure the most noticable issue, the condensation, at the expense of needing electricity to power them and generally being noisy irritating things.

 

But that does not cure the poor air quality.  for that you need proper ventilation.

 

I keep seeing people recommend DMEV or PIV for this, but all that does is blow in fresh cold air or suck out stale air with the same amount of cold air being sucked in any way it can.  Neither have heat recovery so while they will improve the air quality, they will cool the house / increase heating required.

 

Yes for sure for best results you want an air tight house.  But I don't understand the logic of saying mvhr is a waste of time if the house is not air tight.  If you do fit mvhr to a leaky house, at least some of your ventilation will benefit from the heat recovery.  Balance the system properly so you are not pressurising or depressurising the house and little else will enter or exit through all the leaks except perhaps on a windy day.  

 

I would certainly say if you get the chance go ahead with mvhr.

 

Since I appear to be in the minority here, I await incoming.

 

Whilst I recommended PIV, I'm going for MVHR in my renovation. This is mainly because as part of that renovation we're paying special attention to insulation and airtightness.

 

If it wasn't for gutting the place already (to attend to those two points), there's no way I'd be considering MVHR in an existing building, it's a pretty big job to retrofit, whereas PIV alone to mitigate the direct problems makes the most sense in the majority of cases. 

[MarkyG82]

I am of the same view as prodave. I'm still designing our system around an extension based renovation. Upstairs only is easy and what a mate has done. Our downstairs is easy to do a basic in and out at opposite ends of the house. The hard bit is getting the supply to the living room. Still working that one out. I believe it will be worth the effort though. Even in a 1970s detached house.

[HughF]

There’s no way I’m fitting ventilation that doesn’t have heat recovery, blowing cold air in, or sucking out hot air and creating drafts is a total no-no and won’t get past my wife.

 

If it wasn’t moderately airtight then it wouldn’t suffer from condensation, mould and stuffiness, surely?

 

and as for the dehumidifier, I’ve already got two that we use for drying out clothes, but they’re hateful, noisy things that suck 500w (desiccant type)

[Radian]

16 minutes ago, HughF said:

If it wasn’t moderately airtight then it wouldn’t suffer from condensation, mould and stuffiness, surely?

 

Good point. Maybe worth rigging up a DIY test...

That thread could do with some more input 😄

[MJNewton]

1 hour ago, ProDave said:

Since I appear to be in the minority here, I await incoming.

 

No, you're in good company!

 

I retrofitted MVHR to a 'reasonably leaky' (never measured but it's a 2007 Persimmon with dot-and-dab plasterboard etc etc so can't be great) and it is superb. Were it not for the difficulties with such a retrofit I would unreservedly recommend it to anyone.

 

Passivhaus published a research paper in 2020, whose summary conclusion was:

 

Quote

[...] the perceived need for high levels of airtightness is based on outdated assumptions, and suggests that MVHR systems are, in fact, desirable in nearly all domestic situations, either new-build or retrofit.

 

If retrofit is a barrier then certainly worth exploring PIV too. This thread on the Pistonheads forum is worth a read - full of loads of people who have had great success with it.

Edited January 22, 2023 by MJNewton

[Roundtuit]

1 hour ago, ProDave said:

But I don't understand the logic of saying mvhr is a waste of time if the house is not air tight.  If you do fit mvhr to a leaky house, at least some of your ventilation will benefit from the heat recovery

I didn't say it was a waste of time, just that I'd hesitate before retrofitting it, due to the cost and inevitable disruption as you run the ducting and the reduced benefit you may get from the heat recovery.  I also don't disagree that ventilation is key;  'heat and ventilate' has long been the mantra for keeping your house dry.  A dehumidifier was a quick, unobtrusive fix for me in an imperfect house; just worth a thought that's all...

[JamesP]

1 hour ago, HughF said:

There’s no way I’m fitting ventilation that doesn’t have heat recovery, blowing cold air in, or sucking out hot air and creating drafts is a total no-no and won’t get past my wife.

 

If it wasn’t moderately airtight then it wouldn’t suffer from condensation, mould and stuffiness, surely?

 

and as for the dehumidifier, I’ve already got two that we use for drying out clothes, but they’re hateful, noisy things that suck 500w (desiccant type)

Regarding MVHR  even with heat recovery, during the recent low temperatures the incoming supply is about 16c which is then constantly lowering the internal room temperature which then requires more  UFH input.

Wondering if it is worth switching the unit off during these periods or is this a limitation of MVHR.

[ProDave]

5 minutes ago, JamesP said:

Regarding MVHR  even with heat recovery, during the recent low temperatures the incoming supply is about 16c which is then constantly lowering the internal room temperature which then requires more  UFH input.

Wondering if it is worth switching the unit off during these periods or is this a limitation of MVHR.

16C is way better than the 0C or less it would have been here for the last few weeks if you did not have heat recovery.

 

turn off the ventilation and you have poor quality stuffy and probably moist air.

 

MVHR is not perfect but it is way better than the alternatives.

[JamesP]

4 minutes ago, ProDave said:

16C is way better than the 0C or less it would have been here for the last few weeks if you did not have heat recovery.

 

turn off the ventilation and you have poor quality stuffy and probably moist air.

 

MVHR is not perfect but it is way better than the alternatives.

Thanks for the reply. I do appreciate MVHR in the new build, do some MVHR systems have a heater to boost the heat recovery supply?

[SimonD]

1 hour ago, MJNewton said:

Passivhaus published a research paper in 2020, whose summary conclusion was:

 

This isn't really a research paper and in my view it's unfortunately flawed both in its assumptions and conclusions. I've critiqued this paper on one of the other forums and suggested how dissapointing it is to see such a poor quality publication from an organisation that really should know better. It clearly needs to do its research properly, particularly around natural ventilation strategies. It reads more like an industry sponsored paper trying to sell additional tech.... What it actually needs to do is differentiate between building fabric design as well as geographic local and local climate in order to come to more a more reliable conclusion.

 

6 minutes ago, ProDave said:

MVHR is not perfect but it is way better than the alternatives.

 

I do think MVHR has its place, but I think it's important to position ventilation in terms of whole house design and function, which it rarely is. If you've got a house/building that has been built for high levels of airtightness but uses non-moisture buffering materials as part of its fabric, then MVHR is most likely the only option due to the ventilation requirements such a design requires. This is because the greatest burden of mechanical ventilation is down to the removal of moisture as opposed to air quality.

 

On the other hand, if the fabric of the building is designed to be fully moisture buffering, hygroscopic, and vapour permeable, this can reduce peak internal relative humidity by as much as 25% which massively reduces ventilation requirements and therefore properly designed natural ventilation strategies are both effective and energy efficient.

 

As you said earlier though, the op has multiple issues fundamentally caused by the fabric and lack of ventilation all which lends itself to some kind of MVHR , although with the single room options, I'd be concerned that they don't provide sufficient flow and movement through the whole house.

 

I'll await the incoming now....😁

 

[MJNewton]

1 minute ago, SimonD said:

I'll await the incoming now....😁

 

😁

[MJNewton]

29 minutes ago, JamesP said:

Thanks for the reply. I do appreciate MVHR in the new build, do some MVHR systems have a heater to boost the heat recovery supply?

 

They do, but your house already has its own heating system which is likely to be more efficient (or certainly no less) than that provided by one in/around an MVHR.

 

Even at relatively low supply temperatures (eg 16C like you say) I've never noticed a cooling effect from the system. It must of course being doing so, but it's not noticeable in terms of cold draughts etc.

Edited January 22, 2023 by MJNewton

[JohnMo]

Atamate_SDAR+Paper+2019+(1).pdf

 

[HughF]

All interesting points of discussion, thanks. I’ve solved the problem for now by flying somewhere warmer, dryer, and with better building quality 🤣

 

Back in the hateful UK end of the week though. Back to looking at the solutions to this problem.

[AliG]

Clearly opening windows is not the long term solution, but before spending money and time fixing this, it is probably good to know how big the problem is.

 

By the description the house I assume it maybe just has a bathroom upstairs and kitchen downstairs.

 

Can you try opening the windows in these rooms just slightly for a few days to see if that modest amount of ventilation is enough to stop the condensation? It will be quite a bit warmer next week so less of a hit having windows open.

 

I would assume that most of the condensation comes from showers, cooking or clothes drying?

 

If so perhaps a through the wall MVHR unit in the rooms where this happens is all that is necessary. These are cheap and just require a 100mm core through the wall plus electricity, so can be installed without interfering with the occupants. You could maybe just in stall one in the kitchen or bathroom and see if that is enough before installing another one.

 

A full MVHR system or centralised extraction is going to be very expensive to install. and a dehumidifier very expensive to run with current electricity prices.

 

[HughF]

It’s my wife’s house where she lives with her sister. My wife works from home so it’s occupied and heated pretty much 24/7. Single upstairs bathroom, small downstairs kitchen. 
 

Indoor air quality and winter condensation is the main issue as we’ve been on a draft proofing and sealing up mission to try and make it less expensive to heat. It is a very exposed end of terrace, on a hill, facing south west, in the south west.

 

I’m sure when it was single glazed with coal fires in every room, it didn’t have a condensation issue. Most of the condensation is on upstairs bedroom windows, so I suspect some upstairs ventilation is required.

 

Indoor air quality has improved since I’ve banned them from smoking inside 🤣 I’m pretty sure the condensation is the result of an increase in clothes drying (she has an open vent dryer in the outhouse, which I’m about to replace with a heat pump dryer) in the house and baths/showers. They don’t cook much.

Edited January 26, 2023 by HughF