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@Sparrowhawk Indeed the false ceiling was a design decision to hide any ducting and steel.

@ectoplasmosis I will post up a bit more later, we are building a timber frame extension to the rear to allow for a ground-floor bedroom for the mother-in-law.

@Sparrowhawk Ah yes sloppy copying of cell format with the volume. J2 and 3 were me looking at the areas of the rooms with supply or extract. not that they do anything really in the table. the MVHR unit will be placed in the loft and the duct runs are most definitely diagrammatic at the moment. As for the joist direction, there is a false ceiling, which enables the ducts to run free. other than an annoying steel beam the only place the direction is an issue is the living room. I am currently looking at the duct routes to see if I simplify it

hi@ToughButterCupindeed I have spoken to a couple of companies and as suspected received differing approaches, and thought I could have a go at making a complete balls up of it on my own.

Hi all I am new here. Currently, I am extending and remodelling our terrace house. I have had a look at the design for an MVHR system see below my calculations I have based it on information that I have put together from looking on this forum Originally I had thought that I would use 75mm ducting. However, looking into it a bit more it might be better to use 90mm. if my calculations are correct then I would only need to double up the ducts to the Kitchen and Living room. I have looked at the most onerous duct (Kitchen) and have evaluated that the Pa over 12m with three bends and vent would be approximately 50. if anyone can see if I am going off track I would love to know. Below is the ducting and outlet for the ground floor. Red for extract, blue for supply Bellow ducting and outlet for the first floor