Condensation in bedrooms. Positive Input Ventilation PIV?

[rangor gubbins]

Anyone got experience with installing a PIV fan unit?
Our house is old-ish, but has been refurbed with lots of insulation and double glazing, there are no radiators and all heat is provided by underfloor heating and an ASHP. When we put the (wooden) windows in we decided not to have trickle vents. For most of the year its fine but when its very cold outside we get quite a lot of condensation on the windows and its goes mouldy.
Running the wood burning stove helps a lot, but I'd like a more constant solution to the condensation. I originally thought that we should retrofit some trickle vents. However, our house is in quite an exposed position and i think we'd get a lot of draft coming through the trickle vents.
I'm wondering if positive input ventilation would work.
It would be installed so that it will move air from our loft (which has lots of insulation in and under the rafters, so is not cold) to the main corridor on the first floor, which connects the bedrooms and bathroom. But I'm not sure whether it will reduce/stop condensation in the bedrooms if there is not much air gaps in those rooms for the fresh air to push out the humid stale air.

 

[rangor gubbins]

If you have a warm loft PIV needs to be installed above that. Otherwise you would just be moving the same air from one room to another rather than from outside to in.
Have you thought about a dehumidifier?

above the loft is the outside!
The loft is well insulated but i don't think its air tight. i see what you're saying though, we might just be moving house air from the loft to the first floor, and it finds it way back up there again, without bringing much fresh air in.
Maybe i should do some humidity measurements and see what the levels are in the first floor and loft.

I guess an alternative setup would be some kind of MVHR system, with ducting bringing in air from the outside.

 

[rangor gubbins]

Thanks for the advice everyone.

 

[rangor gubbins]

We've got EmonPi from OpenEnergyMonitoring installed, and they do add-on temp and humidity sensors. I'll buy a couple of these to check temps and humidity levels in bedrooms and loft before biting the bullet on installing a PIV.

 

[rangor gubbins]

@b0rn2sk8 thanks for the suggestions.
First point, while it is a warm loft, it isn't sealed to the outside and there are gaps so *I think* air would be pulled in from outside if a PIV was installed. Having said that, I do agree with you there's a risk that pushing air from the loft into the first floor won't help because most of the air in the loft has simply come from the first floor rather than the outside. We might end up just circulating air between the loft and first floor. But if there is enough gaps in the loft that we get outside air coming in, then the air we push to the
I've picked up some humidity and temp sensors, which i will put in the loft and bedrooms and compare temps and humidity for a few nights.

I'm not keen on running a dehumidifier, due to space of where to put it and cost of running. However, if we did install a PIV and it didn't work well enough I did think we could add a dehumidifier into the loft to lower the humidity of the air being push down.
We do open the windows, but this is only practical if unless one of us is working from home, I don't want to leave them open all day. Also if its raining we get rain blowing inside as the house is quite exposed to the elements.
Trickle vents. definitely something we're considering.
decentralised ventilation and heat recovery - will look into this some more. Thanks for the video.
MVHR, as you say, i don't think we can do this.

 

[rangor gubbins]

Firstly, try and eliminate the possible source of the problem, ease tally the humidity being created in the house.

Do you dry clothes inside, either on a clothes horse or radiators, do you use a proper extractor in the kitchen (that vents outside) and extractors in the bathrooms?

Also, how old is the house, is it solid wall (say pre-1930s) or a cavity? The wrong internal insulation inside an old house can cause no end of problems, they were not designed for it. It's really complicated and many people will get it wrong, even some soo called experts.

Clothes are dried in a condensing tumble dryer in a separate part of the house.
Kitchen has a proper extractor venting to outside. Bathrooms are the same.
House is about 1910, with solid brick walls.
Internal insulation is plasterboard backed with PIR (25 mm i think), dot and dabbed onto the original wall. No signs of damp on the walls, only condensation on the windows.

One thing that has dawned on me, we haven't used the shower in the bathroom on the first floor for a few weeks (it needs repairing), and there also hasn't been any condensation in the bedrooms for the past couple of weeks. Might be a coincidence, or maybe i just need to improve the extractor in the bathroom.

 

[rangor gubbins]

When you say it is not sealed to the outside, what do you mean? I'd expect there to be a few small vents for trickle ventilation but that is about it.

A PIV isn't a golden ticket some people make it out to be, they work well in specific circumstances but not in others. If your house is fairly well sealed which is sounds like it will be without any trickle vents, it is not going to work well if there is nowhere for the air to go and it will be like taking a wee into the wind. Likewise, it is the same for when you are running extractors in the kitchen/bathroom, if there is nowhere for the air to enter, you'll not be extracting anything.

The windows thing was explained a few posts above, the idea isn't to open them for a long period of time, its to do it for just 3 minutes to air the house and and close them all gain.

A dehumidifier will not cost much and may not be anything more than running a PIV or fully venting the house daily. That you spend in electricity, you save a bit in heating costs from less air changes. You also wouldn't need to run it all day every day, a few hours overnight will probably be sufficient.

But fundamentally, your house sounds like it lacks a bit of ventilation, it is a requirement under building regs to have vents or mechanical ventilation across the house, that is usually in the form of trickle vents in a typical build or MVHR in a high performance build.

I mean the loft has some air flow which i think is coming in somewhere around the wall plate. It not loads, but when its windy outside you can feel some air movement.

The house is well sealed, but it certainly not a passivehaus, there are still little gaps around the place, plus the ducted extractor in the bathroom. If air is pumped into the first floor from the loft, won't it find the easiest a way out somewhere, e.g. through the bathroom ducting for the extractor, or any other gaps around windows? The loft hatch might need sealing so the air doesn't just go in circle between loft & 1st floor.

You are right, the house needs a bit more ventilation. The question is how best to achieve this.