Positive Pressure Ventilation

[Nintendofan]

Not sure if this is the correct section as there isn't a ventilation section but here goes. I've got a new build house with a positive pressure ventilation system with outlet on the landing, I have no trickle filters anywhere and a single extractor fan that's on 24/7 in the utility room that's as far as you can get from the landing outlet.

I have a bathroom and en-suite that have no extractor fans at all just an opening window. Now the weathers getting colder after a shower as you can imagine there's a lot of steam in the bathroom/en-suite. Naturally I open the window whilst showering but how long after should I shut the window and should I then just leave the bathroom door open, allow what's left of the steam out and allow the positive pressure unit to do its job?

 

[MJN]

Is it definitely a positive pressure system? I am surprised it would meet the building regs for a new build given the lack of explicit extraction (and the counter requirement for air tightness).

As to your specific question though, I suppose the only answer is 'until humidity levels resume to normal levels'. Would be worth getting some humidity sensors to enable you to work out how long it takes in practice. Basing it on apparent levels of steam is unlikely to be effective.

 

[Nintendofan]

Is it definitely a positive pressure system? I am surprised it would meet the building regs for a new build given the lack of explicit extraction (and the counter requirement for air tightness).

As to your specific question though, I suppose the only answer is 'until humidity levels resume to normal levels'. Would be worth getting some humidity sensors to enable you to work out how long it takes in practice. Basing it on apparent levels of steam is unlikely to be effective.

Yes definitely positive pressure ventilation, it's a Nuaire Drimaster. Why would it not meet current building regs?

 

[MJN]

I didn't think a new build would be 'leaky' enough to enable the PIV to function correctly, particularly without the likes of trickle vents. I guess it does though, at least on paper? Does the bathroom clear of its own accord without the window being open? Note that with continuous whole-house background ventilation it will inevitably take longer than what you might be used to with localised extraction.

 

[Nintendofan]

I didn't think a new build would be 'leaky' enough to enable the PIV to function correctly, particularly without the likes of trickle vents. I guess it does though, at least on paper? Does the bathroom clear of its own accord without the window being open? Note that with continuous whole-house background ventilation it will inevitably take longer than what you might be used to with localised extraction.

But doesnt a local extraction system (negative pressure ventilation) rely on the same principle of the house being 'leaky' to replace the air extracted? I always though PIV was better as at least the air travels through a number of filters first and bad air expelled.

By the way the EPC certificate shows how 'leaky' the house is and says Air Tightness Air permeability 4.4 m³/h.m² (as tested).

 

[MJN]

But doesnt a local extraction system (negative pressure ventilation) rely on the same principle of the house being 'leaky' to replace the air extracted?

It does, but I was assuming that with it being a new build and with a design that includes continuous mechanical ventilation that they'd also be aiming for high air tightness levels and so might have provisioned for improving localised ventilation such as trickle vents in wet rooms.

I always though PIV was better as at least the air travels through a number of filters first and bad air expelled.

Oh absolutely, not to mention being far more 'active' and controllable e.g. doesn't depend on which way the wind is blowing etc! With

By the way the EPC certificate shows how 'leaky' the house is and says Air Tightness Air permeability 4.4 m³/h.m² (as tested).

So that does meet the building regs but is arguable leaky enough to enable PIV to function. It's a difficult one really as the approved documents don't explicitly cater for PIV and so it's left to manufacturers and test institutes to justify equivalence of the regs (noting that the approved documents are just examples of how the regs can be met - they are not the regs themselves and are not exhaustive).

Back to your issue/query, I'd do some testing to see how it is actually performing. Presumably there's a boost function that can be used, and you could perhaps look to seeing if that can be automated so as to respond to rise in humidity and not have to rely on manually presses of a button (which I certainly couldn't rely on my family necessarily doing!).

 

[Nintendofan]

Back to your issue/query, I'd do some testing to see how it is actually performing. Presumably there's a boost function that can be used, and you could perhaps look to seeing if that can be automated so as to respond to rise in humidity and not have to rely on manually presses of a button (which I certainly couldn't rely on my family necessarily doing!).

The PIV is on 24/7 but has an automated control where it switches off if the ambient temperature of the loft is above a certain temperature.

Also no trickle vents in any room, when queried with builder they stated that they're not needed for a PIV system and removing them helps keep the outside noise down as well.

 

[JP_]

I think you need an extractor fan in the bathroom. How old is it? Tell the builder to install one if you've only just moved in.

 

[Nintendofan]

I think you need an extractor fan in the bathroom. How old is it? Tell the builder to install one if you've only just moved in.

But wouldn't the negative pressure created by an extractor just work in opposition to the PIV

 

[JP_]

But wouldn't the negative pressure created by an extractor just work in opposition to the PIV

I don't think so - the PIV is sending fresh air into the house, it needs to leave somewhere. But of the bathroom has no vents or extractor, then how will the steam get out of that room, of the pressure in the landing area is higher?

My understanding is that PIV is to continuously push stale air out of the home which can help stop mould and associated damp problems - as mentioned, it is usually in older homes with poor insulation but lots of ventilation, ie drafts.

In a new build, that air has to escape somewhere. If there are no trickle vents (which I though all new builds had to have in all windows?) then how does the air ever get out?

But on a more practical level - you want to get the steam out of the bathroom and en-suite asap, not wait for the steam to drift through your bedroom, down the stairs, and through to wherever the utility extractor is. Well, it would never get that as it will likely condense somewhere along the way.

Seems pretty off not to put ventilation in bathrooms - that's taking energy efficiency too far IMO!

 

[Nintendofan]

I don't think so - the PIV is sending fresh air into the house, it needs to leave somewhere. But of the bathroom has no vents or extractor, then how will the steam get out of that room, of the pressure in the landing area is higher?

My understanding is that PIV is to continuously push stale air out of the home which can help stop mould and associated damp problems - as mentioned, it is usually in older homes with poor insulation but lots of ventilation, ie drafts.

In a new build, that air has to escape somewhere. If there are no trickle vents (which I though all new builds had to have in all windows?) then how does the air ever get out?

But on a more practical level - you want to get the steam out of the bathroom and en-suite asap, not wait for the steam to drift through your bedroom, down the stairs, and through to wherever the utility extractor is. Well, it would never get that as it will likely condense somewhere along the way.

Seems pretty off not to put ventilation in bathrooms - that's taking energy efficiency too far IMO!

wouldn't the pressure in the bathroom not be the same as the rest of the house (i.e greater than the outside) once the door is opened so the moist air will be forced outside where the pressure is less? that's the theory anyway.

Also from reading up a PIV system it is more suited to a modern air tight house as it can then create the positive pressure it needs to work. In an old house with lots of drafts etc. as you mention the PIV system wouldn't be able to pressurize the house to work properly.

You mention building regs requiring all new builds to have trickle vents, apparently you can substitute these vents with mechanical ventilation in every room, as the PIV system works the entire house I presume this is the reason I don't have them and the house was still signed off.

 

[Harry Bloomfield]

But wouldn't the negative pressure created by an extractor just work in opposition to the PIV

My two pennarth - no, with air flowing in, it needs an outlet. The outlet works much better if it is a planned outlet, taking air from rooms where it can do most good, ie the bathroom, kitchen and utility rooms. Basically anywhere where smells or moisture are generated. Forced extract ventilation trumps natural ventilation.