Home Forums General Discussion What impact do ventilation systems have on heating performance

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    Nik Gregg

    Hey Team

    I’ve had a wee look (must admit, not a hard look), have read the Otago and Beacon studies on ventilation – but, has there been any other work, about what impact do ventilation systems have on the heating / temperature of the home? It seems to me that it’s a positive upside during the day and a negative downside at night? But…is this substantiated by any study anywhere?




    Hey Nik, I’m going to follow up and see if anyone got an alert to your message. i wasn’t alerted to this being sent out.

    On the ventilation, the Otago study is probably the most robust in terms of actually measuring temperatures. I haven’t read it in detail for a while but encourage you to do so.

    For another interesting case study see this from Richard P on p. 50 of the attached.

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    Jo Wills

    This is an observation from my own home, relevant to the article and case study mentioned but not specifically to Nik’s question. We had HRV installed years ago (before I have the knowledge I have now), and since working for CEN and learning via the HPA programme I have turned the system off (last year). It’s been incredibly dry in Tauranga for about the last 3 -4 months, although we are just starting to get rain again now. My partner and I have both made comments on how the house feels dry even though it’s raining outside, both times we mentioned it was during the day and with temperatures warm enough to not need heating – but very very wet (90mms over a couple of days). This is significant because the inside air always used to feel damp whenever it rained (summer or winter) and it’s so remarkably different now that we both noticed it. And the HRV system has been off for about a year. We have also done other things such as topped up our ceiling insulation, lined the curtains and put in an extraction fan in the kitchen. Curious.

    Andrew Pollard

    Hi Nik
    The primary function of a ventilation system is to reduce moisture.
    The Otago report showed there is not a large opportunity for these systems (roofspace forced air ventilation systems) to provide heating or improve temperatures within the spaces.
    They may be some heating/temperature advantage during the day however the Beacon work showed that during the day the roof space humidity levels were elevated and using a system during the day may not deal with the moisture appropriately.
    BRANZ currently is undertaking work within an experimental building on ventilation strategies and this will include some information on heat transfer…

    Norman Smith

    I know about four years ago HRV commissioned Professor Robyn Phipps at Massey to carry out a study into all this stuff. Good old EcoBob ran a strong debate on this, something over 120 comments, last year I think. Here is one, go to Ecobob for more. Cheers, Norman

    Re: HRV Units
    Posted 4 Jun 10 11:20 AM
    Hi all.

    Robyn Phipps has done dozens of studies over the years, the latest one was presented by her on the SB10 Sustainable Building Conference in Wellington last week.
    About R. Phipps: http://seat.massey.ac.nz/staff/profile_short.asp?StaffID=20129

    Some examples of quotes for her work:



    Vicki Cowan

    I’ll find and attach the presentation Lisa Burrough did on the BRANZ study. As Andrew says (since he did a lot of the work) essentially the air was warmer in the roof space during the day when it was sunny – but it was wetter than inside the house. And at night time the air was much colder inside the roof than in the house. So the forced air systems were pumping damp air into the houses during the day and cold air at night. Not at all an ideal situation, and certainly not one leading to an overall warmer drier home. So not really a positive upside in the day time.
    The study recommended that the thermostats be humidistats as well so that the systems only operated when the roof air was warmer AND drier than that in the house. I’m not aware that any manufacturer has actually done that.

    Norman, I tried the links you suggested, but they don’t work? I am aware of Robyn’s study and have a copy of her paper, but I didn’t see the presentation at SB10. From what


    Hi Team, I thought I’d pitch in on the old positive-pressure issue. Below I will mention a specific brand-name product. Hopefully that’s within the rules of the hub….

    Lois is right. Until recently, there were no PPVs available in NZ that included humidistats. Most of the available PPVs are controlled on roof temperature alone, and could therefore actually increase humidity in the home.

    A local supplier SIMX has recently started marketing a product called Smartvent Evolve. This system includes three humidistats – mounted in the roof, suffit, and interior. It has a setting which specifically targets dew point. This is interesting, since many homeowners are concerned primarily about condensation on glass.
    According to the manufacturer, the system only operates when the air source will reduce humidity. Once dew point on the windows is above the outside temp, the system shuts down.

    It appears therefore that the design addresses the two main criticisms with PPVs – unnecessarily increased heat load, and wetter houses.

    It will be interesting if the any of the other manufacturers/ high-pressure-sales-people follow the lead on this and release comparable products.

    Today one of my clients decided that they want to install one of these new-fangled systems (against my reservations…). Once it’s installed I’ll pass on their feedback.

    Phil Squire

    Thanks Simon. I was just up at my parent’s home in the weekend. They have a reasonably a 1900 concrete house with thick walls and no dampcourse between the foundations and the walls. Hence some wicking of moisture (though the house is raised above the theoretical wicking height- whatever that is).

    Anyways, the southern rooms get awfully cold and damp in the winter, and are usually unused. The best practice theory is that they open the windows every day but my guess is that the humidity in the house isn’t going to be affected by passive ventilation. So I’ve recommended they install a heat transfer system (from the lounge log burner) to the other three back rooms. From my own experience with a standard gas central heating, the internal pressure differences in various rooms also encourage internal/external air exchange, and in their situation the addition of heat (from an existing source) and some forced ventilation may yield the result they are after.

    Norman Smith

    Hi Phil,

    Heat transfer systems can be great to at least break the cold in other parts of the house but do require the log burner to have reasonable capacity. If your folke have been running theirs to heat, but not overheat, their lounge they will need to burn more wood to create more heat for the other rooms – you don’t get nothing for nothing. However, if their log burner is of a modest size (12-14 kW) it may be pushed to generate enough surplus. Having said that its a modest investment and a realtively straight forward DIY if they have a dilligest and attentive son to carry out the installation! [Don’t forget to ensure the ducting is well insulated]

    Cheers, Norman

    Scott Willis

    Hi all,
    Yesterday a community member dropped promo material and a quote he’d received for a “Solar Pro” system. It may be nowhere else in the country at present as the material tells me “Solar Pro is an Otago & Southland Company that specialises in Heating and Ventilation systems. Soar Pro’s Solar Air Panel System has been created designed and thoroughly tested right here, with each one getting manufactured by ourselves in our Invercargill premises.”

    Still, I’d be interested in any independent information there is on this system, as we’re starting to see it promoted now.

    “How it works: The suns energy passes through our specialised polycarbonate extrusion lid and is absorbed by the solar collector inside. Warm air is taken from the roof cavity and drawn under then over Solar pro’s collector, transferring energy available to the passing air. The heated air is then put through a specialised filter and fan system before being ventilated throughout your home.”

    The promoters offer it as “either a stand alone ventilation system or simply attached to your existing ventilation system”.

    Interested in any information anyone has on this product (apologies for brand name use, but necessary) or concept – it appears to me to be an innovative new way of getting rid of money.

    Oh, its all on the web too: http://solarpro.co.nz/
    I’ll definitely be keeping an eye out for anyone who has installed this system. Great thread BTW.

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    Norman Smith

    Hi Scott,

    I recall HRV were doing some work on such a system, will troll the memory banks.

    Its situations like this when I think a designated Home Performance Adviser should contact the company directly and ask them about the system. What is wrong with someone representing CEN fronting up to SolarPro asking for as much technical detail as possible so all advisers can talk to households about the system from an informed position?

    If it works then advisers will be valuable to SolarPro as they will recommend their system; and if they are not forthcoming or it doesn’t stack up then that’s valuable information for advisers quickly obtained.

    What do people think about formalising such a process when all new products arrive on the market which profess to be better at catching mice or slicing bread? Sure as heck this is not the first ‘amazing energy saving’ technology and won’t be the last.

    Cheers, Norman

    Scott Willis

    Would be very valuable to formalise such a process.

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