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Overnight Heat Loss

  • 23-03-2023 9:51am
    Registered Users Posts: 735 ✭✭✭


    What is acceptable overnight heat loss for a new build A2 rated house?

    To test ours, I turned the thermostat down to 14 degrees from 10pm to 8am.

    The was a 4 degree loss (from 19.8 to 15.8) in the living room. The stat is in the hall and got down to 16.5.

    Outdoor temperature was between 6 and 8 degrees during the night.

    Is this a normal amount of heat loss? Or could it indicate a lack of insulation or other problems?



  • Registered Users Posts: 875 ✭✭✭keno-daytrader

    Seems a huge problem in an A2 house.

    For comparisons our house goes from 22 going to bed to 21.5 in the morning with no heat on at night, with outside temp at night between say 0 and 5.

    Do you know what level insulation is in the floors, walls and attic, also do you have an airtightness test result?

    ☀️ 6.72kWp ⚡2.52kWp south, ⚡4.20kWp west

  • Registered Users Posts: 735 ✭✭✭gandalfio

    Air tightness result is 4.51. The house has an air to water heat pump and central extract mechanical ventilation.

    The builder is refusing to tell me what insualtion was used.

    This is their latest response 'We don’t provide or give out information to customers with regards to materials used'

    I've asked our solicitor for the Outline Specifications that should be included in the contract. Again, being told they done have them. 'We only deal with title, not structure' was their response.

  • Registered Users Posts: 735 ✭✭✭gandalfio

    Wound you have any advice on how I can evidence the overnight heat loss? I took a photo of the stat before bed, then again in the morning. Also took a photo of my own thermometer reading. Is this enough do you think if the builder leaves us with no option but to take this further?

  • Registered Users Posts: 388 ✭✭Biker1

    As the airtightness test result is so bad I would suggest that along with bringing fresh air through the vents the MEV unit is also drawing air in through the building fabric.

  • Registered Users Posts: 21,464 ✭✭✭✭Alun

    I've no idea what our BER is, but it's probably in the C bracket somewhere, and the most we'd lose overnight would be around 3 degrees on the coldest nights, around 2 degrees the last couple of nights. We were away last week and left the heating off and it dropped to around 16.5 degrees after a day and stayed there the whole week.

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  • Registered Users Posts: 1,786 ✭✭✭DownByTheGarden

    Ours is B2. On very cold night, if it there was frost outside all the rooms would lose about 3C overnight. These days its about 2C loss overnight.

  • Registered Users Posts: 735 ✭✭✭gandalfio

    Would this be happening even though the nearest MEV ceiling vents are in the kitchen and downstairs bathroom? There's no ceiling vent in the living room, just a normal vent in the wall.

    Is there a possibility then that the 4 degree heat loss is simply as a result of the bad air tightness result (which is below 5 so passes regulation), and nothing to do with potential missing insualtion?

  • Registered Users Posts: 33,657 ✭✭✭✭Penn

    There may have been confusion regarding the "central extract mechanical ventilation". You have mechanical ventilation for rooms such as the kitchen, bathroom, toilet and Utility, but natural background ventilation (wall vent or trickle vents in windows) for rooms such as the living room, bedrooms etc.

    As such, your heat loss is occuring through the wall vents. Air tightness relates to testing the air loss through the fabric/structure of the building (walls, floors, ceilings, joint between wall and windows/doors etc). Wall vents are sealed up for airtightness testing so they're not included in the results. Background ventilation is still required for airflow and air changes to prevent a build up of moisture in the air by providing fresh air unless you have a whole-house mechanical ventilation system.

    So yes, your internal temperature will gradually reduce when there's no heating on. If you set your heat pump to 14deg, the heat pump won't kick in until internal temperature drops below 14deg. Insulation and airtightness can only do so much. With background ventilation, you will experience heat loss through same.

    If it's a particularly cold night, you could probably close over the wall vent (if there's a sliding cover on it) which will slowdown heat loss (so long as you then open the vents in the morning), but either way you're better off setting the thermostat at a comfortable level and just letting the heat pump do its job to maintain the internal temperature.

  • Registered Users Posts: 735 ✭✭✭gandalfio

    We always leave the stat at 19 or so overnight. I turned it down just this once to test the heat loss.

    To clarify, are you saying that 4 degree heat loss (during a night where the temperature is 8 degrees outside) is normal/acceptable and has nothing to do with potential lack of insulation?

    If the wall vents were closed during the air tightness test, but the heat loss is occurring through those vents as you say, how could it still achieve a result of 4.51?

  • Registered Users Posts: 33,657 ✭✭✭✭Penn

    I can't judge the fall in temperature overnight because there are too many variables. But I would say it may not be the result of missing insulation.

    The airtightness test is really more of an air permeability test. It test air permeability through the actual structure of the house, so any openings the structure such as doors, windows, wall vents, extracts, are all sealed up during the test. It's about testing the air permeability though the structure, as well as joints in the structure (eg. the joint between wall and ceiling, where the window/door meets the wall, the joint between the wall and floor).

    Poor air permeability results would result in even more heat loss.

    However, there are also ventilation requirements which need to be met, in terms of providing fresh air and removing stagnant air. From the sounds of things, this is provided to your dwelling by wall vents. That does mean you essentially have a hole in the wall to the outside.

    Air permeability/tightness and background ventilation are two different things. I understand it sounds a bit bizarre that houses these days are so designed and constructed to be "air-tight", and then there's a big hole in the wall for ventilation, but they're both serving different purposes and complying with different aspects of the regulations that are taking into consideration together when designing a house.

    If anything, proper ventilation is more important than ever as houses are now so airtight that without proper ventilation, you don't get as many air changes, and then end up with stagnant air, more moisture in the air, and then conditions which can lead to mould growth.

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  • Registered Users Posts: 735 ✭✭✭gandalfio

    Regarding your final paragraph with houses now being so airtight, I think it's clear my house isn't air tight enough with a score of 4.51. Which could mean an increased impact of the wall vents on heat retention and loss.

    I suppose I'm trying to figure out if I've any recourse against the builder. But if its the vents causing the issue, and the ATT being below 5, then fair enough and I might have to let things lie.

  • Registered Users Posts: 33,657 ✭✭✭✭Penn

    No, for new houses if you have natural/background ventilation, your result should be between 3 and 5. As such, your result is likely in compliance with the regulations. If your air permeability result was less than 3, you should have mechanical ventilation throughout the house.

    Personally, I would suggest a loss of 4deg (from 18deg down to 14deg, over a period of I'm guessing 7-8 hours) with an external temperature of 8deg, is probably reasonable with no heating on. Again, there are too many variables to consider, but the air permeability result and the method of natural ventilation, imo, appears to be sufficent and in accordance with regulations.

  • Registered Users Posts: 33,657 ✭✭✭✭Penn

    If your wall vents are just open cores with a plastic grate over, you could potentially install a humidity sensor wall vent.

    These vents have sensors which only open when humidity gets above a certain level and provides the required air flow, but minimises heat loss because it's less "open" to the external air.But I think you'd be doing so at your own cost/work. It's unlikely that there's just cause for the builder to install these for you unless you can prove there's an issue or incorrect design.

  • Registered Users Posts: 735 ✭✭✭gandalfio

    Thanks for your advice

  • Registered Users Posts: 735 ✭✭✭gandalfio

    Tried this overnight, closed over the sliding cover. The results were similar, 19.8 degress at 10pm, 16.3 at 06.30 this morning. Is this to be expected even with the vent closed?

    Here's a photo of the vent style

  • Posts: 0 [Deleted User]

    All I can tell you is that my A3 rated, passive ventilated, house, was 19 downstairs at 11 last night and it's currently 18 down there.

  • Registered Users Posts: 875 ✭✭✭keno-daytrader

    Just curious, if you remove the vent, can you tell what insulation is in between the outer leaf and inner leaf, if any.

    Also tonight, I would close the vents and turn off the central extract, see if that makes a a difference.

    ☀️ 6.72kWp ⚡2.52kWp south, ⚡4.20kWp west

  • Registered Users Posts: 33,657 ✭✭✭✭Penn

    There would generally be a plastic sleeve inserted into the core hole in the wall, so no you wouldn't be able to check the insulation.

    Again, I'm sorry but there are too many variables to judge. Room size, orientation, window size, external wall area. You could even be losing the heat through faulty seals in windows or doors.

    Sliding the cover over on the vent can reduce some of the heat loss or prevent draughts, but it's still a hole in the wall. You are going to lose heat through it. It's like having a window open by two inches. If you pull it over so it's only open by one inch, you might lose heat slower, but not much slower.

    If you had a building survey carried out before buying, I would suggest contacting the surveyor/engineer and querying it with them.

  • Registered Users Posts: 11,357 ✭✭✭✭the_amazing_raisin

    I'd suggest checking your local library for a home energy savings kit

    I haven't used one myself but they usually include a thermometer you can use to find cold spots on your walls

    If the interior walls are cold then that would indicate poor insulation or cold bridging

    I think your problem may be cold draughts however. I've a similar issue in my house, when the wind is from the right direction it will cause a draught though the bedrooms which cools the place down rapidly

    It's annoying, but it doesn't necessarily mean the house wasn't build to regulations

    Usually the vent covers have a very simple closing mechanism, you could try closing it down to see if that improves things. Unfortunately that will affect your indoor air quality, so make sure to air the house as much as you can during the day

    "The internet never fails to misremember" - Sebastian Ruiz, aka Frost

  • Registered Users Posts: 2,833 ✭✭✭MicktheMan

    A couple of temperature data loggers would do this.

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  • Registered Users Posts: 190 ✭✭KAMG

    I tested the 2 thermostats in our house last night. One in utility room and one in our walk in wardrobe. Both set at 14 degrees at 10 pm last night. The utility room was 20 degrees last night and was 19 degrees this morning. The walk in wardrobe was 19 degrees last night and was 18 degrees this morning.

    Our house is also A2 rated and completed in 2016. There is a problem somewhere with your house.

  • Registered Users Posts: 2,833 ✭✭✭MicktheMan

    I suppose I'm trying to figure out if I've any recourse against the builder. But if its the vents causing the issue, and the ATT being below 5, then fair enough and I might have to let things lie.

    The builder is covered with the att result being below 5 m3/hr/m2@50Pa.

    What you need to remember is that, for most house shapes, an att measurement of 5 is very close to a full volume of internal air being exchanged with out door air every 12 minutes (i.e. 5 times per hour) when a 20mph wind is blowing outside. I reckon your heat loss issue is likely not insulation related.

  • Moderators, Society & Culture Moderators Posts: 3,934 Mod ✭✭✭✭Turner

    I find even when closed if the wind is blowing hard these vents let in a lot of cold air.

  • Registered Users Posts: 735 ✭✭✭gandalfio

    How do I turn it off? See attached photo of the control panel we have. It's always on auto. If we use one of the other 3 settings, it will come back to auto after 5 minutes or so.

  • Registered Users Posts: 735 ✭✭✭gandalfio

    I have the commissioning and validation reports for the CMEV system.

    Is there any equivalent assessment or cert required for the background wall ventilators?

  • Registered Users Posts: 33,657 ✭✭✭✭Penn

    With respect, this is what I mean about there being too many variables. Utility rooms and walk-in wardrobes are going to have less external wall area, less window area (particularly for living rooms which will always have larger windows, and windows will not be as thermally resistant as the rest of the wall), less floor area, possibly a lower level of background ventilation.

    Not all A2-rated houses can be judged together on something like this. Different means of construction, different levels of insulation, different amounts of renewable energy, different sizes and orientations of windows.... They cannot be evenly compared on one factor because achieving an A2 rating is based on different balances/results of a lot of different factors.

  • Registered Users Posts: 735 ✭✭✭gandalfio

    To ensure that the ventilation ducts are sealed to the air tightness barrier?

  • Registered Users Posts: 875 ✭✭✭keno-daytrader

    If its not isolated with a switch, turn if off at the fuse box.

    ☀️ 6.72kWp ⚡2.52kWp south, ⚡4.20kWp west

  • Registered Users Posts: 735 ✭✭✭gandalfio

    Should the supply air flow rates from the wall vents have been measured? When can I find this information? It's not on the commissioning or third party validation reports.

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  • Registered Users Posts: 875 ✭✭✭keno-daytrader

    I agree, not all A2 rated houses will perform the same. But with all due respect, this house is acting like a C or D rated house. The op is losing >4 degrees of heat in a room overnight when the outside temp is a warmish 6-8c. What will this be like when its 0c out, I would think the heat pump will absolutely eat electricity trying to keep up in the dead of winter.

    Something is wrong here if you look at the other posters posting their heat loss numbers.

    I would spend the money on an independent heat loss survey, this will probably answer and identify most of your issues in the house. I hope you find the answers, as this sounds like a very frustrating situation.

    ☀️ 6.72kWp ⚡2.52kWp south, ⚡4.20kWp west