Home Forums General Discussion Positive pressure systems and heating

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    Jonny Parker

    Hi Guys,

    I’m keen to track down some information on PPS effect on heat within the home. I’ve had many customers complain that they feel cold even when the heating is up full. I’ve suggested they try switching off the PPS when they run the heating to see if they feel warmer. Some have reported that this works but I haven’t had feedback from everyone.

    I’ve always suspected that these systems can reduce heating performance by introducing cooler air from the attic space. However Consumer’s recent curtain study has found that blown air from fans within the home can actually break up the stratification of heat and reduce heat loss?

    Can anyone point me towards a study of PPS effect on home heating and I’m not sure what we should advise?

    Ian McChesney

    Hi Johnny
    As we head towards winter the temperature of the air blown from a positive pressure system sourcing from the ceiling cavity will become increasingly cold, especially in evenings and throughout the night, because it reflects ambient external temperatures rather than any short term heat storage offered by a ceiling cavity during the day. Under still night air ceiling cavities can even become colder than ambient.
    So, no surprises that people feel cold from positive pressure systems. And it is a different ‘cold’ than that referred to by Consumer – they are talking about mixing the heat that is already contained within the room to minimise stratification and maximise its warmth effectiveness; a PP system introduces an additional source of cold air which will diminish the warmth in the room.
    I wrote a report on home ventilation systems for EECA in 2009 – the report is on their website and link is below:

    Bear in mind that this report is 6 years old now, and there are a better range of balanced pressure/heat exchange systems now available

    Norman Smith

    As general comment, the ability of such systems to provide ‘free’ heat from the roof cavity is over the shoulder periods of spring and autumn when there can be a temperature difference between roof cavity and the living space. In summer this warm air boost is not needed and in winter its not there. Cheers, Norman

    Jonny Parker

    Thanks Guys, That’s a great resource Ian, I’ll tell the other assessors to check it out.

    Vicki Cowan

    Lisa Burrough (then BRANZ) did some work in this space when we were in our reserach consortium phase, here’s the link to the page:

    Christian Hoerning

    Hi Jonny,

    These links might help you:

    EECA energywise webpage on ventilation systems:

    Otago Uni report “Heating and cooling potential of roof space air: implications for ventilation systems”


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