Ventilation

[John Brown]

Any ventilation experts here?
The house we moved into in August is a barn conversion, done maybe 30 years ago. It is all double glazed, and has dreadful condensation problems.
At the moment we have a dehumidifier on the upstairs landing which has stopped the mould appearing on the walls, but I am thinking this is probably a short term solution. Last night it was pretty cold here in Gloucestershire, and the inside of the oak front door was dripping with condensation when I went to bed. Admittedly we have a very full house right now, with 6 adults and 4 grandchildren.

Anyhow, I was looking at the idea of positive input ventilation, with the device in the attic that blows fresh air into the house, when I realised there is no fresh air in the attic. The rafters are covered in 10mm of Kingspan, and there seem to be no eaves/soffits or anything.
Can I get some sort of PIV system to pull in fresh air from outside into tye attic, and thence through ports into the house? Is this feasible? Any other suggestions?

 

[Rorschach]

This time of year all you will do is bring in cold damp air and make your problem worse.

 

[Rich C]

This time of year all you will do is bring in cold damp air and make your problem worse.

At this time of year the outside air is actually pretty dry because cold air holds a lot less moisture.

 

[sunnybob]

Condensation occurs when hot humid air meets a surface colder than 20c.
And also when said hot air meets cold air.
People breathe out hot humid air. The more people, the more hot air ( :shock: :roll: )

The only certain way of stopping condensation is to get the outer surfaces above dew point, or keep the air in the room below 20.
Most people dont want to live in a room that cold so in a barn conversion with stone walls that are almost certainly not insulated, youre on a hiding to nowhere. Central heating works best because it dries the air. Open fires and gas flame fires make it much worse.

The absolute WORST thing you can do is inject more cold air. If you could get a portable air conditioning unit and set that to heat, blowing the hot air towards the outer wall in the worst condensation area, you would improve matters quite a bit.

 

[John Brown]

I think our walls are fairly well insulated. The temperature only drops by a degree or so overnight, when the heating's off.
So are all the testimonials about PIV just plain wrong?

 

[sunnybob]

I dont know what PIV is, sorry.
Get a couple of thermometers, place them one in a corner of a bedroom and 1 low down behind the front door. No good checking the temp on a thermostat set in the middle of the room, that isnt where you get condensation. Get the lowest temp to 22 c and the condensation will disappear. But your heating bill is going to scare the pants off you.
Or, send everybody home. :roll: =D> :shock: :lol:

 

[John Brown]

I have checked temp and humidity in numerous locations, and logged it to spreadsheets. The problem is ventilation, I'm fairly certain.

 

[Petehpkns]

Hi, We have a converted Chapel School with a mezzanine, so a large open space. When we first moved in 4 years ago we had a similar problem.

Other than heating the place the solution is adequate ventilation, so agree a PIV would work. We actually just use the wall vents which are the original fit, and simply leave them open year round, which works.

Because the kitchen is open-plan we also made sure any moisture is vented and fitted a cooker hood to cope.

Hope you find a fix....

Pete

 

[HappyHacker]

I installed a PIV for a customer with a stone house which suffered form damp in some of the walls. His damp proof man recommended it. The customer was very happy with it and said his damp problem had been resolved. But the air is cold from the attic in winter although there is a small built in heater which takes the chill off the air. There is very little water in cold air so it does not add to any damp/condensation issues.

My daughter currently rents out her small house which is reasonably insulated but a couple of the tenants have complained about condensation. The main cause is drying clothes, baths/showers and cooking and windows not being opened. There is cold bridging around the windows and the top edges of the external walls in the bedrooms.

The only solutions to condensation are to reduce the amount of water in the air or to stop the walls getting colder than the dew point of the air. Extractor fans can help with the first and the second is more difficult in an existing house. Extractor fans get rid of all the warm air in the house as well though. The alternative is the heat recovery extractor fans but I have no experience of them.

 

[Rorschach]

This time of year all you will do is bring in cold damp air and make your problem worse.

At this time of year the outside air is actually pretty dry because cold air holds a lot less moisture.

Cold air does hold less moisture of course but we are in the UK, it's wet all year round and the air outside still has plenty of moisture in it during the day. You do not want to bring that into your house.

 

[Rorschach]

From a cost perspective in the colder months you want to use a dehumidifier to dry the air and keep the warmth in. You can ventilate but to get enough ventilation to dry everything out you are are just blowing all your expensive warm air outside and on mild days the air you are bringing in is just cold and wet and will make your problems worse.

Close the vents, run the dehumidifier, it will be cheaper and better in the long run.

 

[John Brown]

In our old house which was built in 1894, we had no double glazing, and numerous draughts. All the moisture ended up on the windows.
This house is heated to around 22 during the day(my wife's American, they seem to like hot houses), and really only drops a degree or two over night. But there is almost no ventilation, apart from three or four trickle vents in window frames. I can't realistically ask the family not to breathe, or not to shower or cook, for that matter, but the humidity upstairs(without the dehumidifier turned on) gets up to around 70%. So when I read about PIV, I thought maybe it was worth a try.

 

[SammyQ]

John, I've just (a month ago) had PIV fitted. Condensation on our D/G windows disappeared that night and has not returned. Cost was approx 40%, or less, of mechanical heat recovery - itself not an option in an older bungaloid like ours.
We had hidden terminal mould in two rooms, that I heavily suspect the previous owners threw massive heating bills at to suppress it. [When we moved in a year ago, we had to replace a 6 year old gas boiler/C.H. source that blew up 10 days later. Its guts were completely knackered]. So far, so good, so we would be one of the positive P.I.V. reviews. No estimate of electric costs yet, but the two fans are reputed to be 8W and 4W respectively. Installation was 3 hours, dust and mess free, and straightforward. Only repair was to relocate the shower extraction (humidity sensing fan) directly above the cubicle, and then close/replaster the old aperture.

H.T.H. Sam. P.M. or follow post if you want more gen.

 

[John Brown]

Thanks, Sam, for those words of encouragement.
What make is yours, and does it pull in air for the loft, or directly from outside?
Maybe I'll call one of the suppliers next week and have a chat. The fitting is possibly within my capabilities.

 

[SammyQ]

Environvent. Pulls air from the loft, but has built-in heater for Arctic periods. Output is via a vent in our roof, just above first roof tile. Internal fixings might be easy, but unless you are confident on slates/tiles, I would think carefully about piercing felt and slate/tile replacement. They do this every day and have a van-full of hardware.
If you are in N.E. U.K., around NewKassel (as they pronounce it here), I can give you a contact for this area's rep, one A. Hunter. If not, Head Office is pleasant to deal with; lass there on the 'phones is cogent and intelligent.

Sam

 

[John Brown]

We have Cotswold stone tiles, so I would not attempt that.
Not in north east, situated between Bristol and Gloucester.
However, I will call them next week, and the other crowd "Nuaire".
From what I've read, I thought the exhaust route was via the various natural leaks and gaps in the building. But I'm no expert, obviously. Until Friday morning I'd never heard of PIV.

 

[Rorschach]

Yep great, spend money heating your house and then blow it all out again through the roof. :roll:

While you are at it, get rid of all the insulation you put in and open all your windows.

 

[SammyQ]

Yep great, spend money heating your house and then blow it all out again through the roof. :roll:

While you are at it, get rid of all the insulation you put in and open all your windows.

No, No, No, gently does it Man. I - as an empirical scientist - was as full of doubt as you are. But, the 'turnover' of air is so gentle, that the heat imparted by our gas boiler has time to soak into the fabric of our wee building before the humidity sensing fan in the bathroom sucks the air out. I know, sounds like snake oil, but Deity Dammit(!!) it works!
I have a dependent with a compromised immune system, for whom humidity+fungal spores represents a catastrophic complication. This P.I.V. system takes away a component of that scenario, that would otherwise lead to said complications, so they are nullified. It does so with less thermal emphasis than I expected, and I am - if not 'converted' - at least impressed. And I am one of the most cynical sons of she-dogs you are likely to meet on a day's walk.

Sorry Rorschach, gotta 'suck it'n'see' in this case.

Yes, I know, I don't yet have the figures to objectively measure thermal impact, so I may yet have to 'eat crow' in that respect, but the health rewards are hard to put a value on.

Sam.

 

[Fitzroy]

Thought I’d run some numbers. You know just for fun. I like to live on the edge on a weekend.

100% relative humidity water content of ai r:
At 5 Celsius is 6.8g/m3
At 10 Celsius is 9.4g/m3
At 20 Celsius is 17.3g/m3

Average sized house is 250m3.
Fairly air tight house 0.75 air changes/hour.

Average person water respired & perspired is approx 800g per day.

Any water vapour given off by people or cooking will increase the water content of the air. If this air drops in temperature below it’s dew point then condensation occurs.

Some numbers:
If 5 Celsius air enters a dwelling at 100% relative humidity (common on a damp winters day) and then warms up to 20 Celsius it can absorb up to 10.5 g/m3 water vapour. ( 17.3 -6.8 = 10.5). If this air contacts a surface at any temperature less than 20 Celsius then condensation will occur.

If said air only absorbs 2.6 g/m3 of water vapour then it can contact a surface at down to 10 Celsius before condensation occurs. 100% relative humidity at 10 Celsius = 9.4g/m3 = 2.6+ 6.8.

Based on the assumptions above:
Water give off by family = 8 x 800 = 4800 g/day + 1000g from cooking = 5800 g/day. Assumed 8 adults equates to 6 adults and 4 kids.

Equating to a water content increase of 5800 / 24hrs / 250 m3 / 0.75(hr-1) = 1.28g/m3

Dew point for air with moisture content of (6.8+1.28)= 8.08 is 8.5 Celsius. Condensation will occur on any surface with temperature below 8.5C

At an air change per hour of 0.3, which is low condensation would occur on any surfaces below 12C.

If water content were doubled due to showers and cooking with poor extraction condensation would occur at 15C.

Overall in a house with poor ventilation it’s easy to build up moisture to a level where condensation will occur on even mildly cold surfaces.

I love maths.

Fitz.

 

[John Brown]

Interesting.
So based on that, what's your opinion on PIV?