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  • #1
    Closed Accounts Posts: 5,433 sinnerboy

    Heed the warning

    According to an article in Building magazine, the government is to issue guidance regarding mechanical ventilation systems after a draft BRE study found widespread failure to maintain filters.

    The government is to consult on new building regulations following concerns that ventilation systems required by airtight energy efficient homes could damage the health of residents. The government is so concerned over the installation and maintenance of the systems it will include guidance in a consultation on changes to Part F of the Building Regulations, due in the next few weeks.

    In addition, it has co-sponsored a report with the National House Building Council to investigate the scale of the problem. The draft report by the BRE’s Dr Michael Swainson and seen by Building, found that filters were not being replaced when worn out, which could lead to a build-up of humidity, carbon dioxide and other pollutants, as well as driving up energy use. It also says this could increase the risk of cancer in the homes of smokers.

    Mechanical ventilation systems are required in energy-efficient airtight homes to make sure that fresh air can circulate and that pollutants and humidity are extracted from the house. However, like a hoover, if the filter is not replaced the system stops working.

    The systems are virtually unavoidable if a home is to meet level four of the Code for Sustainable Homes, which all new homes in the social sector must meet by 2010.

    Particular problems occur if extract fans in bathrooms and kitchens are not properly installed because raised humidity can encourage mould spores, leading to breathing problems, particularly for asthma sufferers.

    The BRE’s report said: “There is no market for replacement filters, with several manufacturers reporting no filter sales at all. Even basic maintenance is not undertaken.”

    Swainson has written an addition to Part F for the communities department, which he said would be in the upcoming consultation.

    Kelly Butler, director of The Electric Heating and Ventilation Association, said: “The design’s fine, the product’s great off the bench and then it all goes wrong on site.”

    Credits:: Michael Willoughby,



  • I change mine every 4 months, the filters are a kind of wire frame with a dual-filter made from polyester. The intake always has a lot of black stuff and insects in it. The extract is full of dust and some cooking grease.
    I soak mine in a detergent solution and then agitate until there is no dirt in the water.
    Dry them and wait for the next change.
    I shudder to think what happens if there is no maintenance, not from a health point of view but more from an efficiency POV.

  • Good post. Very interesting article

  • I clean mine Spring and Autumn, I forgot the first year and it was very noticable when the filters were cleaned as the airflow improved dramatically.

  • are the filters reusable on some models after cleaning?

    How much are filters costing to replace?

    I'm putting in one of these MHRV systems as well but would just like to know from current users what the running and maintenance costs are?

  • Running costs are less than 2 x 60w lightbulbs.
    Filters for mine are about €24 per pair, I wash and reuse mine as much as possible.

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  • Ardara1 posted this some time ago here - is is worth posting again

    Take a look at this guidance, emanating from the Canada Mortgage and Housing Corporation recently, on what you need to do to keep your MVHR (which they refer to as HRV) systems tickety-boo.


    Your heat recovery ventilator (HRV) can help make your house a clean, healthy living environment, while keeping fuel bills down. But your HRV can't do all this without your help.
    It only takes seven simple steps to keep your HRV happy…

    The Seven Steps to a Happy HRV

    First turn off the HRV and unplug it.

    • Step 1: Clean or Replace Air Filters
    Dirty or clogged filters can lower ventilation efficiency. Try to clean your filters at least every two months. Filters in most new HRVs can be easily removed, cleaned with a vacuum cleaner, then washed with mild soap and water before being replaced. Older units have replaceable filters. If your HRV is easily accessible, this is a 5 minute job.

    • Step 2: Check Outdoor Intake and Exhaust Hoods
    Remove leaves, waste paper or other obstructions that may be blocking the outside vents of your HRV. Without this vital airflow, your HRV won't function properly. During winter, clear any snow or frost buildup blocking outside vents.

    • Step 3: Inspect the Condensate Drain
    Check to see if your HRV has a condensate drain, a pipe or plastic tube coming out of the bottom. If it does, slowly pour about two litres of warm, clean water in the drain inside the HRV to make sure it's flowing freely. If there's a backup, clean the drain.

    • Step 4: Clean the Heat Exchange Core
    Check your HRV owner's manual for instructions on cleaning the heat exchange core. Vacuuming the core and washing it with soap and water will reduce dust which can build up inside the core.

    • Step 5: Clean Grilles and Inspect the Ductwork
    Once a year, check the ductwork leading to and from your HRV. Remove and inspect the grilles covering the duct ends, then vacuum inside the ducts. If a more thorough cleaning is required, call your service technician.

    • Step 6: Service the Fans
    Remove the dirt that has accumulated on the blades by gently brushing them. Most new HRVs are designed to run continuously without lubrication, but older models require a few drops of proper motor lubricating oil in a designated oil intake. Check your manual for complete instructions.

    • Step 7: Arrange for Annual Servicing
    Your HRV should be serviced annually. If you are not comfortable doing it yourself, contact a technician accredited by the Heating, Refrigerating and Air Conditioning Institute of Canada. Make sure the technician you call has been trained by the manufacturer of your HRV.

    Check Your HRV Balance: the Garbage Bag Test
    HRVs need to be balanced, with the fresh air flow matching the exhaust flow. If you do not know if the HRV was balanced when installed or if you have changed or added HRV ducts, you may want to check the balance with the following simple procedure. This rough test will take about 10 minutes.

    Use a large plastic leaf collection bag, typically 1.2m (48 in.) long. Untwist a wire coat hanger. Tape the wire to the mouth of the bag to keep it open. You now have a garbage bag flow tester. Go outside to where your HRV ducts exit the foundation.

    • Step 1:
    Crush the bag flat and hold the opening tightly over the exhaust hood. The air flowing out of the hood will inflate the bag. Time the inflation. If the bag inflates in eight seconds or more, go to Step 2. If the bag inflates in less than eight seconds, turn the HRV to a lower speed, and repeat the test. Then go to Step 2.

    • Step 2:
    Swing the bag to inflate it and hold the opening against the wall around the HRV supply hood. The air going into the HRV will now deflate the bag. Time the deflation. If your HRV is balanced, air going into the HRV will balance the air coming out of the HRV. The inflation and deflation times should be roughly equal. If you find that the bag inflates twice as fast as it deflates, for instance, your HRV is unbalanced. If you can see no problem with the filters that would cause such an imbalance, you should call a service person to test and adjust your HRV.

    Please don't ignore your HRV. Just a little bit of your time is all it takes to keep it running smoothly.

    • April or May
    — Turn dehumidistat (the adjustable control on many HRVs which activates the HRV according to relative humidity) to HIGH setting or to OFF.

    • September or October
    — Clean core
    — Check fans
    — Check condensate drain
    — Check grilles and ducts in house
    — Reset humidistat (40%–80%)

  • CJ -

    How does the house "feel" - fresh always I should think ?

    Whatever about low running costs - do you believe ( or better still can you demonstrate ) lower heatings costs ?

  • (Hands up - we sell units so are not completely impartial!!!)

    Some good tips on maintenance there.

    Some (but not all) units come with a warning on the control panel that flashes when the filters get blocked - maybe this is something to keep an eye out for when installing a system?

    PS - a lot of filters can be cleaned, just make sure the unit is installed somewhere accessible otherwise it'll never get done.

  • sinnerboy wrote: »
    CJ -

    How does the house "feel" - fresh always I should think ?

    Whatever about low running costs - do you believe ( or better still can you demonstrate ) lower heatings costs ?

    You have it in one SB, the house always feels fresh, no musty smells, or stale cooking odours lingering.

    I guess the running costs are harder to prove, I haven't been keeping records.
    But to my mind the benefit is in the increased quality of indoor air and the lowered humidity inside.
    It will be hard to prove what the difference between having HRV and not having it is because it has been running since we are in the house.

  • CJ - perhaps this is a question you can't answer fully - in a technical sense - so your educated guestimate would be of interest

    Many people ask about HRV in the context of capital costs , running costs , and associated costs to make the building air tight ( to maximise the HRV efficiency )

    Do you think there is a valid health / quality of environment argument for HRV - i.e. even if your house is not very airtight ( I don't mean it can be very leaky now ) and therefore the HRV does not operate at optimum efficiency - still install it anyway . Purely on "comfort" grounds ?

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  • This is an interesting point and TBH I would say that HRV would make a big difference to ANY house as long as the house is reasonably well sealed.
    The amount of dust/insects/black stuff that collects on the intake filter is astounding.
    That tells me that the system is working and that the debris would otherwise be inside the house.
    The difference it makes to the indoor humidity levels in winter is pretty amazing.

    It comes down to 2 ways, either you build a house with 80mm holes in the wall which give freezing cold air on windy days in winter, and none on still, humid days.
    You don't have much choice in the matter IMO.

    I guess there is another benefit that is kind of walked around and that is the offgassing of certain materials and the resultant invisible pollution that is present from materials like MDF, Chipboard, and OSB to mention just a few, the constant circulation of the HRV will also make buildup of these pollutants unlikely.

    It is hard to quantify exactly what a HRV house feels like but a guy that builds concrete houses has installed a few of these and he reckons they make a massive difference to any houses internal air quality.

  • Came across this report from the EU - There's a mad rush for us to tape up our homes as air tight as possible, but there are concerns - we need to join up all the dots in Energy Efficiency strategies/regulations before running headlong into 'Zero Carbon' regulations - I don't think we have the expertise to lead in Europe - but yet our Part L is way advanced of most other member states????

    Ventilation, GoodIndoor Air Quality
    and Rational Use of Energy

    8.5.2 Mechanical ventilation
    Buildings with mechanical ventilation have fan powered supply air to and exhaust air from the rooms. Supply air may be heated depending on demand but not humidified or cooled. Ventilation system may have heat recovery from exhaust air. System may recirculate also return air.Windows may be sealed or openable.These systems are common in countries with
    moderate or cold climate where air conditioning is not always needed to maintain thermal comfort most part of the year.Technical details of these systems for good performance are described in a European draft standard (CEN,prEN 13779,2003).
    Risks in the performance of mechanical ventilation include the following:HVAC-components may be dirty when installed or become dirty and release pollutants and odours;poor control of indoor temperature due to absence of cooling;low humidity in winter;noise generated by forced air flow and fans;draft caused by forced air flows.If the system has mechanical cooling the additional risk factors are introduced by cooing coils: condensed moisture in the system (e.g.cooling coils and drain pans) and potential microbial growth;biocides used to treat wet surfaces such as drain pans. In systems with air recirculation some additional risks are introduced:indoor-generated pollutants are spread throughout the section of building which
    air handling system serves; higher air velocities which increase risk of draft and excessive noise; supply ducts of HVAC-system may become contaminated by indoor generated pollutants.

    .........In mechanically ventilated buildings the ventilation air is conditioned before it is supplied to the rooms via the duct system.Because of supply and exhaust air fans the system is more flexible in respect of building design, and more energy efficient if heat recovery is used.
    However, studies in many European countries have shown that mechanical ventilation systems may cause adverse heath effects,the reasons of which are not yet well known,but the following have been suspected:air handling system is a source of pollution,moisture in air handling system causes the mould growth, system generates and transfers noise, ventilation air supply is poorly controlled, occupants cannot influence the ventilation.
    These issues have to be solved to achieve good indoor air quality.

  • sinnerboy wrote: »
    CJ -

    How does the house "feel" - fresh always I should think ?

    Whatever about low running costs - do you believe ( or better still can you demonstrate ) lower heatings costs ?

    Our situation was: 30+ year old house, no hole in wall vents, well sealed dg pvc windows (original were teak, I think). Had various "moisture" issues in the form of mild mould in external corners of north and east walls, sever condensation on bedromm window glass in mornings, paper often felt damp when left in some rooms, salt in salt seller was damp. And all this even when windows were opened for more that an hour or two a day. Air tightness of the house was measured at less than 3 ach at 50Pa (and this on a 30+ year old house!!).

    We had mhrv installed and straight away there was a big difference in air quality. small things such as the salt flowing freely, window condensation eliminated were very noticeable.

    While last winter was colder than normal, I reckon that the mhrv system contributed to increased heating costs (maybe 10%) but what a difference in the air quality. Had we tried to achieve the same air quality without a mhrv system (by opening windows longer or installing hole in wall vents) I reckon we would have used a significant more amount of oil so I suppose that for good quality air, mhrv does in fact save on energy costs.

    I checked the filters after 5 months and they were quite dirty.