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Old 07-26-21, 08:17 AM   #575
Robl
Helper EcoRenovator
 
Join Date: Oct 2020
Location: Cambridge, UK
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Continuing describing the system we have, in case it's helpful:
It's a Vent Axia Sentinel Kinetic Plus BH unit, which was the biggest I could fit through the loft hatch. Bigger meaning it runs slower and quieter!
I installed it myself, and the ducting is generally 6 inch diameter, the long loft run is even 10inch. Bigger means slower airflow - keeping it below 4m/s is crucial to keeping airflow non turbulent and quiet. The main unit is in our loft, and so are most of the ducts - I used "safe" metal ducting which fits together nicely, and is less likely to cut you. Then it connects to vents that are upstairs, or travels downwards in rectangular plastic pipes (still with the same cross sectional area as the 6" pipes) that are easy to hide in the back of the built in cupboards that our house has. Between the unit and the metal ducts, I used 6" "Tecsonic" insulated ducting, which is supposed to attenuate fan noise, and it allows an easier fit to the unit.
We have fresh air coming into 2 bedrooms and the lounge, leaving from kitchen and bathroom. Not that many places, but I find it works ok, as we have big gaps under doors. I had (lent it out ages ago, didn't come back) a CO2 monitor with a display, and tried it in various places - my conclusion was 1 person in a bedroom with an open door didn't necessarily need a vent, 2 did for sure. We have ~2.5ACH at 50Pa.
To commission the unit, I used a cone over each vent, noting the airspeed (unit at 50%). When I added up the air-outs, they equalled the air-ins, so I didn't bother adjusting the vent axia unit. The vents themselves screw in and out - so you could reduce the airflow - I haven't though, I'm sure this would reduce efficiency. The air mixes in the house, I don't see the purpose in precisely matching some ideal flow rate in each room when what you actually need varies depending on occupancy anyway.
I think we've had it around 8 years. I change the filters every 3 or 4 months when it nags me - remove the old filters, take off the old material (save the clips) so I'm left with the original wire former. Then cut out a new piece of filter from a massive roll of G4 filter I got years ago. The filter clips onto the wire using "Supaclips", and there - avoided spending £20 on new filters again!
I considered diy-ing the heat exchanger itself - they are expensive for what you get. Diy-ing the install gives big savings I'm sure though.
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