What exactly is positive pressure ventilation and how does it fit into your home?
They’re also often referred to as positive input ventilators (PIV) and are often sought out and installed by people who find they have condensation issues in their home.
These systems typically comprise of a small unit which sits in your loft and is ducted through your landing or hallway (in a bungalow) ceiling.It’s ducted in these areas because they’re communal locations and have direct access to the majority of rooms in your home.
Within the unit is a ventilation fan which draws fresh air in from outside your property, either via your loft area (meaning your loft needs to be ventilated) or via a duct direct from outside. The fan then pushes this fresh air into your hall or landing.
As you’re now pushing air into your home the air pressure inside the house will increase, and since air moves from areas of high pressure to areas of low pressure, the moisture laden air within your home is going to try to escape.
This positive pressure air in your house will look for any tiny gaps in the fabric of the building such as trickle vents, suspended timber floors, cracks in walls, gaps around window and door frames and chimneys etc. As the moisture laden air escapes it’s replaced by fresh air from outside thus reducing the chances of condensation occurring within the property.
The main reason they get installed is to try and reduce problems with condensation and black mould in homes. But they can also be installed to improve air quality in your home. Read more on the benefits of ventilation here and whole house ventilation here.
Yes , it can be installed in any property. However that doesn’t mean that it’s ideally suited to any type of home.
A nice modern newly built house which is very well insulated and well draught proofed, in my opinion, would lend itself better to mechanical ventilation and heat recovery (MVHR) because you don’t really want to pump cold air into your lovely warm house at it will cool your house down.
Plus a well sealed home will have limited gaps in the fabric meaning the added air has nowhere to go and that will just stress the motor in your PIV unit.
It is possible to buy a PIV system with a heater, or some systems allow you to add a heater, but I’m still of the opinion that a MVHR unit should still be more efficient. Provided you can install it at the building stage on a two or more storey building.
MVHR units can be retrofitted quite easily to existing bungalows, but gaining access to all the ceilings in a two or more storey house can prove to be tricky and expensive.
Prior to 2000 older properties didn’t tend to be affected by condensation to the same extent as today. Mainly because they were pretty leaky. By which I mean they weren’t air tight and allowed draughts to get in around windows and doors etc. Plus they wouldn’t have been well insulated.
In other words the leaky fabric of the building did the job of the ventilation system.
Today however, we all want out homes as air tight and well insulated as possible. So we seal the gaps around our window frames and fill the cavities in our walls and our roof-spaces with insulation. Which all helps reduce draughts and maintain that precious heat.
But it also means the moist air in our homes doesn’t get to escape and causes condensation which in turn leads to black mould.
As you can see the only obvious disadvantage is the additional heating costs, but I wouldn’t let it put you off. Simply by opening your windows you'll make you heating system work harder and getting rid of the water vapour is essential.
If you have an existing home that isn’t going to suit MVHR and you have a condensation problem a Positive Pressure Ventilation system might just be the answer (or indeed Negative pressure ventilation).
I say MIGHT be the answer because there are a huge number of variables that will contributed to condensation issues. But all things being equal creating positive pressure in your home will reduce the level of water vapour in the air and therefore reduce your risk of condensation.
Positive Pressure Ventilation systems tackle the second one and a heated system will tackle both. Provided you can accept the downsides.