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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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General: Whole House Air Filtration System

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  1.  
    Are there any recommended whole house air filters without going down the MVHR route?
    • CommentAuthorMike1
    • CommentTimeJan 31st 2023
     
    This may be one time where buying the cheapest undersized MVHR unit you can find is actually worth it?
    • CommentAuthortony
    • CommentTimeJan 31st 2023
     
    Boulder one in the loft or one from a major fan company
    •  
      CommentAuthordjh
    • CommentTimeJan 31st 2023
     
    Posted By: Mike1This may be one time where buying the cheapest undersized MVHR unit you can find is actually worth it?
    Not quite sure how you would use this? Why undersized - I'd have thought that was a recipe for a rapid failure and a lot of noise meanwhile?
    • CommentAuthorMike1
    • CommentTimeJan 31st 2023 edited
     
    Posted By: djhWhy undersized - I'd have thought that was a recipe for a rapid failure and a lot of noise meanwhile?
    If filtration is the only concern (as it appears to be), rather than providing a particular air change rate, a cheap unit permanently running on a low setting _may_ be adequate. It would probably depend on the level of filtration required, and what is giving rise to the need for filtration. Hence my question mark above.

    If it needs to provide whole-house ventilation too, a more robust solution would be required. Ideally MVHR...
  6.  
    My daughter has bad eczema and so we're trying to keep all sources of allergies down.

    I intended fitting MVHR years ago but decided the house is probably too leaky (Victorian mid-terrace) to warrant MVHR. We still have open chimneys wedged with pillows in bags for instance
    • CommentAuthorcjard
    • CommentTimeFeb 1st 2023
     
    How would it help then, if your house is so leaky? Or were you thinking of a filtering PIV?
  8.  
    In a similar vane is anyone aware of an iPSV system with filtration?

    Ventive used to have filtration I believe, but they no longer have a PSV system suitable for domestic properties, (and they never answer enquiries so I've crossed them off my list)

    Glidevale iPSV has no filtration.

    We have the double whammy of a neighbour with a highly polluting wood stove and light sleepers who are sensitive to MV noise - I've never come across a truly silent mechanical vent in real life.
  9.  
    Our MVHR is set to quiet mode overnight - you’re not generating as much moisture from cooking or washing when you are asleep so the fan speed goes down lower (and therefore quieter).

    [Vent-Axia Sentinel Kinetic]
    • CommentAuthorborpin
    • CommentTimeFeb 5th 2023 edited
     
    Posted By: Dominic CooneyOur MVHR is set to quiet mode overnight
    About a year ago, I started measuring CO² in the house and on the MVHR extract. I was surprised that the ventilation rate needed to keep the CO² stable and the difference one person made to that.

    Humidity is pretty stable even after showers (well never to the problem levels) and the house is generally too dry and I need a Humidifier. So ventilation levels are basically set for CO² level control. For the 2 of us, that is on minimal setting all the time.

    Side note, I started measuring the Home Office CO² with just me. Horrified at how high it got with the door closed (it has supply but no extract). I now leave the door ajar (and yes it has the gaps under the door) which maintains the level nicely.

    Moral of the story, measure your CO².
    •  
      CommentAuthordjh
    • CommentTimeFeb 5th 2023
     
    Posted By: borpinHumidity is pretty stable even after showers (well never to the problem levels) and the house is generally too dry and I need a Humidifier. So ventilation levels are basically set for CO² level control. For the 2 of us, that is on minimal setting all the time.
    Our MVHR has a 'trickle' setting of 50 m³/hr (approx 14 l/s) and we typically run on that up to 17 hours a day and 125 m³/hr for the other seven (or longer) whilst the heater might be running. I'm curious about your humidity. What is 'too dry' as an RH number?
    • CommentAuthorRobL
    • CommentTimeFeb 5th 2023
     
    Posted By: borpinAbout a year ago, I started measuring CO² in the house and on the MVHR extract. I was surprised that the ventilation rate needed to keep the CO² stable and the difference one person made to that.

    Side note, I started measuring the Home Office CO² with just me. Horrified at how high it got with the door closed (it has supply but no extract). I now leave the door ajar (and yes it has the gaps under the door) which maintains the level nicely.

    Moral of the story, measure your CO².


    We cook, dry clothes indoors, aim for 50% RH indoors. Our VH sentinel+B natively has RH, aftermarket added CO2 feedback(recommend). It can get 50% RH, but we’d need to target lower than that to appreciably drop CO2 lower (maybe 800ppm typical). The unit can easily strip all the moisture out of the air if it tries! Many offices in my experience get lower CO2 than that, but are very low RH in winter - ok for a bit, but people eventually get itchy skin, and pick up infections.

    Measuring RH and CO2 is a first step for anyone interested in air quality - very few people recognise either issue.
  13.  
    Posted By: Mike1
    Posted By: djhWhy undersized - I'd have thought that was a recipe for a rapid failure and a lot of noise meanwhile?
    If filtration is the only concern (as it appears to be), rather than providing a particular air change rate, a cheap unit permanently running on a low setting _may_ be adequate. It would probably depend on the level of filtration required, and what is giving rise to the need for filtration. Hence my question mark above.


    How much money are you really going to save? You still need all the ducting and supply/extract hardware. You still need high quality fans. So the only saving would be the lack of a heat exchanger. But even in a leaky house you'd expect the heat exchanger to add some value to offset the cost of running the fans (vs running the fans without any heat exchange)
    • CommentAuthorminisaurus
    • CommentTimeFeb 16th 2023
     
    <blockquote><cite>Posted By: borpin</cite><blockquote><cite>Posted By: Dominic Cooney</cite>Our MVHR is set to quiet mode overnight</blockquote>About a year ago, I started measuring CO² …. Horrified at how high it got with the door closed

    Moral of the story, measure your CO².</blockquote>

    What is your definition of high?

    Submarines use 3000 ppm I think
    •  
      CommentAuthordjh
    • CommentTimeFeb 16th 2023
     
    https://www.kane.co.uk/knowledge-centre/what-are-safe-levels-of-co-and-co2-in-rooms

    What are safe levels of CO2 in rooms?

    250-400ppm Normal background concentration in outdoor ambient air

    400-1,000ppm Concentrations typical of occupied indoor spaces with good air exchange

    1,000-2,000ppm Complaints of drowsiness and poor air.

    2,000-5,000 ppm Headaches, sleepiness and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present.

    5,000 Workplace exposure limit (as 8-hour TWA) in most jurisdictions.

    >40,000 ppm Exposure may lead to serious oxygen deprivation resulting in permanent brain damage, coma, even death.

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