Positive Input Ventilation advice

[Doug71]

Looking at fitting a PIV to help a damp old house.

Was thinking of maybe one of these Vent-Axia Pure Air Home with Heater Positive Input Ventilation 240V (I know it will be available cheaper elsewhere).

Just wondered about peoples experiences and thoughts on if I needed a heated one like in the link or if the slightly cheaper non heated ones do the job okay?

I was just worried if the non heated would make the house colder this time of year but obviously the heated will cost a lot more to run.

It will be hanging in the loft of a smallish 2 bedroom house.

Thanks, Doug

 

[Fitzroy]

I think the other option is a MVHR unit, where you recover the heat out of the air leaving.

 

[artie]

This old house is pretty damp, I have been running a dehumidifier 24/7/365 and I hate to think what it would be like without it.

My, and possibly your problem is that the humidity outside is as high if not higher than inside and pulling that into the house may not help a lot unless there is quite a good throughput.

I have purchased some gear which will measure outside RH and inside RH and only circulate air when outside RH is lower than inside RH.

I haven't set it up yet cause RH is always high outside this time of year.

 

[Jacob]

Positive air extraction is the other alternative. We've got two "Passivent" extractors in two top floor bathrooms which dry out the rooms very quickly, and the assumption is that they will carry on drawing air through the whole building. They don't need power - they open and close according to humidity.
Seem to work very well.
You need a straightish run to vents fixed close as poss to the roof ridge.

 

[Jacob]

......

I haven't set it up yet cause RH is always high outside this time of year.

But the absolute humidity will often be very low outside in winter and relative humidity even lower if you bring it in and warm it.

 

[John Brown]

Just typed a long reply and lost it....Try again..
Our property is a three or four hundred year old barn, converted 30 or 40 years ago. Solid mudstone walls, oak framed double glazing.
We were getting real problem with condensation and black mould, so I took a gamble and bought a Nuaire Drimaster LC(£267 including free next day delivery from Fastlec).
I was pessimistic, but had to try something.
Installed it on a Thursday just before Christmas. No noticeable difference Friday morning. Went to Surrey for a couple of nights and returned Sunday lunchtime to a different house.
I just wish that I'd done it two year ago, when I was first toying with the idea. I also wish that I'd taken some "before" photos.
Best £300 I've ever spent.
As it happens, I was boring one of my neighbours in the village with this story last Friday, and it turns out he went through the same experience a couple of years back. He also said it was the best 300 quid he'd spent.

 

[John Brown]

I think the other option is a MVHR unit, where you recover the heat out of the air leaving.

Agreed, but not an easy retrofit in our property. Also way more expensive, I imagine.

 

[Jameshow]

Just typed a long reply and lost it....Try again..
Our property is a three or four hundred year old barn, converted 30 or 40 years ago. Solid mudstone walls, oak framed double glazing.
We were getting real problem with condensation and black mould, so I took a gamble and bought a Nuaire Drimaster LC(£267 including free next day delivery from Fastlec).
I was pessimistic, but had to try something.
Installed it on a Thursday just before Christmas. No noticeable difference Friday morning. Went to Surrey for a couple of nights and returned Sunday lunchtime to a different house.
I just wish that I'd done it two year ago, when I was first toying with the idea. I also wish that I'd taken some "before" photos.
Best £300 I've ever spent.
As it happens, I was boring one of my neighbours in the village with this story last Friday, and it turns out he went through the same experience a couple of years back. He also said it was the best 300 quid he'd spent.

How does it not cause the loft to be damp??

 

[John Brown]

How does it not cause the loft to be damp??

Why would it? It's not pushing air from the house into the loft, it's pushing air from the loft into the house.

 

[accipiter]

Interesting information found from the details for the Drimaster LC unit. Got me wondering if I could use such as suffering this year with condensation more than in previous years.

However, I live in a stone constructed terraced property with a build date of around 1796. Not "solid" walls as such as there are random size cavities between the inner and outer faces with smaller stones "filling" (?) the gaps - sort of as per a dry stone wall construction. It also has a double pitch roof, no "landing" as such where I could site the PIV in a ceiling (above the stairs) because the stairway is along the centre wall of the property. Inner pitches of the double pitch roof rest on this wall - sorry if a poor description. Loft openings (as such) are also in the lower pitch areas of the roofs - little headroom... cracked skull if not wary... instead of central to the "ridges" of the roofs.

 

[John Brown]

Interesting information found from the details for the Drimaster LC unit. Got me wondering if I could use such as suffering this year with condensation more than in previous years.

However, I live in a stone constructed terraced property with a build date of around 1796. Not "solid" walls as such as there are random size cavities between the inner and outer faces with smaller stones "filling" (?) the gaps - sort of as per a dry stone wall construction. It also has a double pitch roof, no "landing" as such where I could site the PIV in a ceiling (above the stairs) because the stairway is along the centre wall of the property. Inner pitches of the double pitch roof rest on this wall - sorry if a poor description. Loft openings (as such) are also in the lower pitch areas of the roofs - little headroom... cracked skull if not wary... instead of central to the "ridges" of the roofs.

I believe they sell a wall mounted version, but I have no personal experience of that.

 

[accipiter]

I believe they sell a wall mounted version, but I have no personal experience of that.

Thanks John. I'll look a bit further for that. I messaged them to ask re double pitch roof and they just linked to a YouTube video

 

[NFav]

Well this could be just I need.
We have a 1920's solid brick walled detached house, we've always had to be a bit careful with getting mould spots on the interior of the exterior walls in the bedrooms.
Having fitted Honeywells Evo Home central heating controls, and so the radiators are on much less than they used to be, we can now see visible condensation an the walls. So far we've been having windows wide open, drying the walls with a towel, and running dehumidifiers.
So I'm definitely going to be looking into this.

 

[joncooper27]

Hi if you Have a PIV unit do you still need bathroom extraction or can you get a PIV unit to do bathroom extraction as well?

 

[DeanN]

Another vote for the Nuaire Drimaster. I installed one into my parents bungalow after they had suffered condensation and mould issues for years. It literally cured the problem within 48hrs. No condensation and once the mould had been treated and painted, its never reappeared. I've since installed one into my own house, and again don't suffer from condensation. It also seems to dry clothes quicker - could be down to the fresh air being pumped around the house?

 

[John Brown]

Hi if you Have a PIV unit do you still need bathroom extraction or can you get a PIV unit to do bathroom extraction as well?

PIV doesn't do extraction. It may help with your bathroom situation, but my gut feeling is that you have an extractor you should probably keep it.

 

[porker]

Installed a Nuair Drimaster about 5 years ago in our large old non cavity, single glazed house and it's been great. Turned it off about a week ago to save electricity and it was back on again within 48 hours. I was sceptical when I bought it as I've seen positive and negative reviews but it's worked for me. I bought one with a heater but never used it.

Ideally I could do with one in the other end of the house which is the main bathroom but am going to install dedicated extraction there

 

[joncooper27]

Currently I am refurbing the property I have no extraction in bathrooms yet. The whole house is lime plastered and I have been using breathable clay paint. I currently have a dehumidifier downstairs which has a humidistat in it. It does not run all the time thou.
Just wondering if to use PIV and extract or use 2 x PIV units no extraction or what’s best as I have a freehand at the moment? The other thing is one extract unit connected to 3 bathrooms?

 

[porker]

Personally I would extract in each bathroom whatever else you do. There is a good video on YT where CharlieDIY goes through ventilation and extraction. The only reason I haven't done it in one of my bathrooms is because the roof is about to be replaced and it's easiest to wait and vent through the roof. The PIV is blowing into the hallway so has a more general affect through the house Reducing internal sources of damp is also worthwhile like drying clothes and ventilating the house by opening windows occasionally. By far my biggest problem is teenagers and the shower!

 

[HappyHacker]

A few years agoI installed a PIV for a customer in an old sandstone house. It was recommended by the guy who had done some damp proofing for them as the only way he recommended of getting rid of the damp in their sort of house. It worked for them and they were happy with it. Not sure of the make but it had a small heater in it to take the edge off the cold air bing blown onto the landing. I am not sure about the impact on heating costs and would recommend MVHR but it is difficult to retrofit in most existing properties.