Category Archives: Ventilation Ducts

Above-Ceiling MVHR Ductwork

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The supplier of the MVHR equipment (BPC Ventilation) prepared a design showing the rough locations of the inlet and extract vents, specifying that each vent should have two 75mm semi-rigid ducts attached (in order to achieve the required airflow – especially given the relatively long duct runs). The detail of the duct routing is left to the discretion of the installer. I settled on locating the vents along the centreline of the workshop then running the ducts on the East side – mostly because the access hatches are just to the West side of the central bracing planks, which form a natural walkway – at least for now, before the rest of the loft insulation gets installed. While the 75mm duct (FRÄNKISCHE profi-air classic grey NW75) specifies a minimum bend radius of only 150mm there is no harm in having much larger radius bends where space allows.

Some of the MVHR ductwork above the ceiling in the Workshop. The black plastic moulding is a plenum chamber that feeds the air vent (that will be) fitted below the ceiling.

The loft space will be ‘cold’ (deliberately ventilated to the outside) and I initially looked at pre-insulated ductwork but was advised that’s not as good as it might be and the best approach is to install uninsulated ductwork ‘in the middle’ of the loft insulation. The insulation visible in the above photo is a 100mm-thick layer between the ceiling joists and that – together with the grey ducts – will get covered by the additional 170mm of insulation installed on top.

At their other ends, the ducts connect to another plenum chamber adjacent to the MVHR unit.

The ‘inlet’ plenum chamber feeding the three inlet vents (which each have two 75mm semi-rigid duct connections). The inlet from the MVHR unit is underneath.

Outbuildings: Week 29, Day 4

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Outbuildings: Week 29, Day 4

Still more work on the underground drainage in the Courtyard, this time with a focus on the ground-level drainage (e.g. door threshold drains). The drainage completed so far was inspected by Building Control mid-morning, enabling the trenches to be back-filled before the end of the day.

Completion of the masonry for the second of the decorative buttresses; its lead flashing ‘cap’ will be added over the mortar ‘wedge’ at the top once that has set.

The second (Easternmost) of the decorative buttresses by the garage doors, with its twin in the distance

More work on the ventilation ducts, completing the temporary installation of the below-ceiling ductwork for Supply and Extract and connecting up the first of the flexible ducts above the ceiling.

Ventilation ductwork temporarily installed on the ‘building’ side of the Vent-Axia MVHR unit

The black tubes immediately above the MVHR unit are slightly flexible, to reduce the transmission of vibration from the fans inside the unit to the rigid ventilation ductwork. The two ‘tinfoil’ tubes are silencers, helping to reduce fan noise transmission through the ventilation air to the room vents. (The silver foil is covering fibre insulation surrounding perforated (actually expanded metal) tubes, which are also somewhat flexible.) While these noise-reduction measures are arguably excessive for the intended use of the building, as a Workshop, it will be interesting to see how well they mitigate fan noise that would be problematic for a building used for sleeping.

There will be further 125mm ducts on the left hand side of the unit, connecting it to the external vents for Intake and Exhaust. The two electrical boxes on the left of the photo are the 3A Fuse and the multi-pole Fan Isolator switch to which the unit will be connected. With the initial duct fitting completed – sufficient to confirm the placement of the ‘plenums’ above the ceiling – the unit and the temporary ductwork has been removed again, to avoid damage and dust contamination while the ceiling is plastered.