Coldness/draught from a PIV (positive input ventilation) - is this normal?

oligopoly

I had a PIV fitted a few months ago under the Great British Insulation scheme (plus loft insulation). I felt a draught under the unit in the summer but didn't worry too much as it was warmer weather. Now that it's getting colder I'm worried that this unit is making the house colder. Is this normal for a PIV or has it been installed incorrectly?

You can see a short clip of it here. These are photos hung around 60cm away from the unit and you can see them moving in the draught.

https://youtube.com/shorts/fae0pLdBOHU

Kiran

Yes, completely normal unless you have the heater version. Its pulling in fresh air from the loft which will be cooler at this time of the year and using it to create a positive pressure environment in your house. 

oligopoly

OK thanks. So perfectly normal to increase heating in the house to compensate? Hopefully that won't be normal but I can feel cold air coming out of it. As long as you think it's normal then that's my main concern.

Kiran

It is normal to have the cool air flow from the unit. If you need the temperature higher to be comfortable then increasing your central heating use is the best option. Don't be tempted to isolate or turn the unit off as it is doing what it is meant to do 

rob7475

It's normal I'm afraid. I fitted a PIV unit in our house around 10 years ago. We noticed the cool breeze in winter but turned the heating up to compensate which was fine when gas prices were lower.

PIV works well and cured our condensation issues but the rising gas prices are probably making it outdated technology now. MVHR is the way to go but is much harder to retrofit to older houses.

I removed our PIV last year due to the rising heating costs. Any condensation build up our windows on cold mornings is now dealt with by a karcher window vac.

oligopoly

rob7475 said:

I removed our PIV last year due to the rising heating costs. Any condensation build up our windows on cold mornings is now dealt with by a karcher window vac.

This is what concerns me - I had no condensation issues beforehand. I applied for loft insulation as part of this grant. They installed the PIV first then the loft insulation and then when they came to do the wall cavities they discovered they couldn't due to the timber construction. The cynic in me thinks they just want to get these units fitted as some kind of quota/government mandate. Anyways, thanks for the advice.

FreeBear

MVHR is by far the better way to go. But these units are expensive and can be difficult to install. Palin old PIV systems are cheap and require minimal effort to install. The downside is you now have to heat the cold air coming in, so they cost more to run.

If you didn't have condensation before the PIV was installed, I'd suggest turning it off and plugging the main vent. You can purchase small slabs of PUR/PIR insulation boards from the likes of B&Q. Carefully cut to size, it would plug the hole quite effectively (or just stuff some loft insulation in). If condensation does become a problem, the PIV can be returned to operational status quite easily.

These companies doing work under ECO & GBIS type schemes follow a tick box sheet without any real concern about long term effects/costs for the home owner. The sheet says "upgrade insulation, install background ventilation". It should be saying "assess existing air change, and add BV IF required". Unfortunately, testing air change costs money and takes time.

greyteam1959

The PIV unit may have several different speeds settings.
Refer to the user manual.
If it has turn it down to a lower setting.

Mistral001

PIV's are useful where there the house is almost airtight.  They pump fresh air in, raising the pressure inside the house, thus ensuring that stale air is expelled through doors or windows that are open.  Air cannot come in through open windows and doors because of the positive pressure built up in the house.  

They are also useful in houses which have vents or small gaps in the external envelope, such as at loose fitting windows or external doors.  The positive pressure provided by the unit will ensure that air cannot come in through those places, it can only go out, thus practically eliminating these drafts at the loose fitting windows etc.  So lots of small drafts coming from vents and loose fitting windows and doors will be replaced by one larger draft coming from out of the PIV unit in the ceiling of a hallway or landing, but the house should feel less drafty.   

Albermarle

Mistral001 said:

PIV's are useful where there the house is almost airtight.  They pump fresh air in, raising the pressure inside the house, thus ensuring that stale air is expelled through doors or windows that are open.  Air cannot come in through open windows and doors because of the positive pressure built up in the house.  

They are also useful in houses which have vents or small gaps in the external envelope, such as at loose fitting windows or external doors.  The positive pressure provided by the unit will ensure that air cannot come in through those places, it can only go out, thus practically eliminating these drafts at the loose fitting windows etc.  So lots of small drafts coming from vents and loose fitting windows and doors will be replaced by one larger draft coming from out of the PIV unit in the ceiling of a hallway or landing, but the house should feel less drafty.   

I would guess though that if you had a house with loose fitting windows, doors etc. you would not have a problem with condensation, which is the usual reason to fit a PIV I think.

FreshAirMan

It sounds like the draught you're experiencing is a typical issue with Positive Input Ventilation (PIV) systems, particularly in colder weather. PIV units introduce fresh air into your home without conditioning it, which can create noticeable draughts. This is especially problematic in winter months, as the cold air enters your home directly, potentially making your living spaces feel colder. This issue may persist even if the system has been installed correctly. If you're looking for a more efficient solution that avoids draughts, you may want to explore Mechanical Ventilation with Heat Recovery (MVHR) systems. MVHR captures the heat from outgoing stale air and uses it to warm the incoming fresh air, ensuring a more comfortable indoor environment.