Ceiling Vents to Help Heat Escape House at Night - Would It Work?

tomclancy on 29/11/2020 - 08:29

I'm trying to find out if installing cheap ceiling vents would help the heat escape our house on summer nights. Cheap ceiling vents like this one from Bunnings: https://www.bunnings.com.au/pacific-air-200mm-round-ceiling-…. Something that can be closed for winter. I'm no tradie but could easily install something like these and cut the insulation out above them.

The reason I'm wondering is because our bathroom is always substantially cooler at night than neighbouring bedrooms with the same aspect and the only things different about it are a ceiling exhaust fan and concrete/tile floor. Is the exhaust fan (aka vent) or the flooring making the biggest impact in terms of removing hot air at night? During the day they are the same temperature, it's only at night that it cools down quicker - very much in line with outside temps, whereas the living areas of our house retain the heat until the morning.

Our situation:
- old house in Sydney
- double brick walls
- 3.3m ceilings with good insulation above
- terracotta roof tiles on about 45 degree pitch angle
- hardwood floors with heaps of gaps and no insulation below
- all windows and doors double-glazed and sealed air-tight (we live on a busy road so was done for noise)
- no air conditioning and no plans to install it

The windows and doors only go to 2.1m high so there is effectively a 'box' of trapped hot air above them of 1.2m high. Opening windows doesn't do much if there's no breeze. We have one or more brick wall vents on the internal skin of the walls in every room (including the bathroom) but not convinced they are doing anything.

If putting a ceiling vent in every room makes even a small difference I'd probably give it a go since the price is negligible.

Are there any HVAC experts that could share some of their expertise?

Poll Options

  • 12
    Ceiling vents won't do jack
  • 2
    Ceiling vents will help a little
  • 3
    Ceiling vents will help a lot
  • 9
    I like pressing buttons
Home & Garden

Comments

  • charzy on 29/11/2020 - 08:44
    +2

    Open windows + multiple fans to create air flow throughout the house.
    If you must install a vent get a whirlybird as it's geared towards hot air escaping. You'd still want insulation in winter. I'd avoid this option though as double brick is designed to insulate and thus your house should be an oven if heated over the course of a day.
    Personally I'd get air conditioning if insulation is great, air con can run effectively. Start to run it in the morning before the hot day starts and it should effectively maintain temps throughout the whole day on the lowest setting.

    • tomclancy on 29/11/2020 - 10:03

      If you must install a vent get a whirlybird as it's geared towards hot air escaping

      Isn't that geared towards roof space? I'm trying to figure out why our bathroom is so much cooler at night then neighbouring rooms with the same aspect (under the same roof).

      Personally I'd get air conditioning if insulation is great

      Yeah, we'd like to avoid air con. We haven't needed it for past 16 years here and it's not uncomfortable to live here. The only issue with heat is in summer when there's a 3+ day heat wave and then when a cool change comes through we can't seem to let all the hot air escape even with windows open

      • charzy on 29/11/2020 - 11:24
        +2

        It is geared towards roof space. However have you been to the roof to see how hot it is? Chances are your roof is much hotter than your living room.
        If the roof is hotter than the top half of your living room, then hot air won't migrate from living room to roof.

        . The only issue with heat is in summer when there's a 3+ day heat wave and then when a cool change comes through we can't seem to let all the hot air escape even with windows open

        Most of the heat resides in the bricks. It takes a long time for the bricks to warm up (hence why brick houses offer good insulation), unfortunately it also takes long time to cool down (like an oven).
        Best bet is either allow heat to escape constantly e.g. whirlybird/whrigigs to allow heat to escape from roof so it keeps rising, or to promote airflow throughout the house e.g. create a wind tunnel for air to keep moving.

        • tomclancy on 29/11/2020 - 19:14

          Yeah, thinking airflow is most important too

  • jimbobaus on 29/11/2020 - 09:33
    +1

    Whirligigs are what you want ;)
    They are very effective at venting hot air out of enclosed spaces

    https://www.bunnings.com.au/csr-300mm-bradford-windmaster-na…

    We had a similar issue in one of our investment properties, tenants were complaining it was super hot in summer.
    We installed new air cons but also fitted these in most rooms.
    The tenants advised us they didnt need to use the air con as much as the air flow in the house drastically improved.
    They are far more effective and cost efficient than a window + fan soloution

    • pharkurnell on 29/11/2020 - 09:44

      These x lots.. they let the heat escape the roof cavity and make a world of difference.

    • tomclancy on 29/11/2020 - 10:07

      Agree with this generally, though I thought it was not as effective on a tiled roof because it already has air gaps between tiles.

      Also, as per my comment above I assume whirlybirds are geared towards roof space ventilation but with a well insulated roof/ceiling then would it make a massive difference to the living space? And why is our bathroom cool when other neighbouring rooms tend to trap hot air (well that's what it 'feels' like)

      🤷

    • MondaySleeper on 29/11/2020 - 10:28

      Thanks for the suggestions, @jimbobaus

      "We installed new air cons but also fitted these in most rooms."

      I thought this is fitted on the roof. if you fir this in the room, between ceiling and roof, wont it reduce the efficiency of AirCon? Sorry if the if the question is dump. I am also looking for something similar. My house roof is tiled and there is sarking which I think would block getting air in and out of roof??

      • jimbobaus on 29/11/2020 - 12:14

        Hot air rises
        They find that they turn air cons off sooner as the heat escapes quicker etc.

        Not sure if the science but these are not a one size fist all solution they just assist in air flow etc.

  • brad1-8tsi on 29/11/2020 - 10:47
    +1

    They will only help if you hook them up to whirly birds on the exterior of the house.

    your roof temperature will be 10c-25c hotter and the thermo syphon effect that you seek won't work

    • tomclancy on 29/11/2020 - 19:14

      That makes sense. Thanks

  • scrimshaw on 29/11/2020 - 11:49
    +1

    I have no ceilling vents but have ducted air conditioning, but instead of turning the AC on to cool the house, simply open all the windows on the 2nd storey and turn on all the fans I have in all the bedrooms to create some air turbulence. Eventually the temperature will equalize with the outside temperature but it does take 2 or so hours.

  • skid on 29/11/2020 - 11:55
    +2

    Is the exhaust fan (aka vent) or the flooring making the biggest impact in terms of removing hot air at night?

    It's the tiles vs hardwood floors that is making the biggest impact due to the difference in thermal mass.

    • tomclancy on 29/11/2020 - 19:15

      Yeah right, thanks

  • endotherm on 29/11/2020 - 12:03
    +1

    Does the bathroom have windows, and if so, how large are they? Are the bathroom walls made from the external brickwork or are they lighter internal walls? The positioning and makeup of the bathroom may explain why it is cooler than the rest of the house.

    Also, the "vent" you listed in the OP is actually an outlet for forced air delivery from an A/C system or similar, not an exhaust vent.

    • tomclancy on 29/11/2020 - 19:19

      Yeah the bathroom has a window, exactly the same aspect as the neighbouring bedroom and office the other side too. All walls double brick externally and single brick internally. Positioning, aspect, build method same for all.

      Also, the "vent" you listed in the OP is actually an outlet for forced air delivery from an A/C system or similar, not an exhaust vent.

      Yeah, I know. But functionally it's just a vent that can open & close. Doesn't matter if air goes up or down through it. Just wanted something cheap

  • tebbybabes on 29/11/2020 - 15:13
    +1

    I can add that in my last place, one of the bedrooms was markedly warmer than the rest of the adjoining rooms that were on the same floor. Everything on the 2nd floor was heaps warmer, but that one bedroom was markedly so. They shared walls, similar construction and the same roof. When we were working in the roof space, we discovered that the part of the roof space overlying that bedroom also had a concentration of warmer air compared to the rest of the roof space. It was only a couple of degrees difference in an already extremely roof space, but noticeable nonetheless. We surmise that it was just how heat and the convection currents concentrated in that particular area.

    • tomclancy on 29/11/2020 - 19:20

      Hmmmm interesting

  • ozbargainsam on 29/11/2020 - 15:21
    +1

    I was actually looking into this myself to normalise the roof space temperature to the outside to potentially put some Wifi access points up there (rated to 70°C).

    It's also a full brick but 2-storey home with full insulation. Ducted aircon is installed.

    Something like this I read was better than the simple whirlybird: https://www.bunnings.com.au/ezylite-200mm-solar-roof-vent-fa…

    • tomclancy on 29/11/2020 - 19:21

      Sounds like forced airflow is the way to go.

  • [Deactivated] on 30/11/2020 - 18:11
    +1

    I have an old Victorian house and while I regulate the temperature through a large ducted reverse cycle, I find that most of the heat in the house is actually retained and radiated by the brick walls (double and triple brick all around). It's often hotter at night after the sun goes down, than during the day. I can cool the air temperature easily, but the hot walls mean that the second I turn the system off, the house starts heating up again.

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