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MHRV Install - DIY Complete

  • 27-10-2021 1:27pm
    Registered Users Posts: 607 ✭✭✭ tedimc

    Hi all,

    We had our house renovated a few years back and got it first fixed for MHRV and Vacuum. It was a Beam install and a Ostberg/Heru MHRV unit, which is in place, but not commissioned.

    I'm considering finishing off the install myself, I just need to fit the extract and supply valves for the MHRV and the vaccum unit and hoover ports.

    What are the guidelines for the extract and supply air flow rates for MHRV? I presume it boils down to M3 of air per hour, per M2 of living area? I know I need a mechanism for measuring airflow, but I presume it is straightforward to configure the vents and MHRV unit myself?

    I'm confident with the work done to date on the ducting etc, but for a few reasons I would be more comfortable completing this myself. I'm looking for guidance on how I should set these up and any issues I should look out for.



  • Registered Users Posts: 256 ✭✭ Biker1

    You could buy a powered flow hood for around €700, then learn how to calculate the required flow rates for each room and commission it yourself or you could just pay a NSAI Ventilation Validator a couple of hundred to do it for you.

  • Registered Users Posts: 2,150 ✭✭✭ Yellow_Fern

    A nice touch is to have a special extract duct with a local filter for the kitchen to catch airborne soot.

    What kind of ducting do you have? What do the expert lads here think of plastic flat channel ducting? is it to be avoided?

  • Registered Users Posts: 607 ✭✭✭ tedimc

    Are they that expensive?? I'd have no problem getting someone in to validate or commission it. What I want to avoid is someone coming in, cutting back the ducts, installing the valves, etc. I also need to clean out the ducts anyway in advance and ensure each connection is clear. I also want to connect the unit into my home automation system.

    If I done all that, would someone just need to adjust the flow rates on the valves?

  • Registered Users Posts: 607 ✭✭✭ tedimc

    Ducting is a mix of spiral metal (~12 inch) on the main runs and then reduces down to ~5 inch plastic for tee offs. All round ducting.

    Not an expert, but I heard in the past that airflow is better in a round or oval duct as opposed to rectangular. I can't see it being a huge issue on a short run though.

  • Registered Users Posts: 2,150 ✭✭✭ Yellow_Fern

    Thanks. I was doing reading and it looks like one company has flat channel that has the edges rounded (ComfoTube Flat 51) so a compromise and thus is actually shallower than normal flat channel (138 x 51mm).

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  • Registered Users Posts: 1 soks07

    Hi im installing my mhrv myself diy job on a new build, and i my intake, exaust vents are exiting through slate vents, but my problem is that from where they are exiting my unit they must fall to get to slate vents is that a problem or must they rise from unit to exit roof? all help wud be greatly appreciated