Ventilation of suspended timber floor with deadend

[Endless to do list]

I have a 1930s semi-detached house. The property has previously been extended to both the rear and most of the side. The extensions have solid floors but the original rooms have suspended timber floors. I have attached a diagram of the layout. The orange crosses represent existing clay airbricks.
Due to the additions, there is no crossflow of air under the timber floor. I haven't lifted the boards yet to see the condition but the floor seems sound.

To provide vetilation, I was considering placing some ducting at the end of the 'deadend' and connecting it up an unused chimny near by (shown in green). In addition, I was planning on adding a couple of new airbricks to the side and replace the existing ones with greater flow plastic ones. I would then seal the chimney around the ducting, so only air from under the floor cold be drawn up the chimney.

Is this an acceptable way to provide ventilation?

The alternative would be to break out the concrete floors to lay ducting through to the back of the house, but I would prefer to avoid this if I can.

 

[foxhole]

Should not be needed, though surprised extension does not have vents installed.

 

[Endless to do list]

The rear extension was done in two parts, I suspect the first section was probably ducted but the previous occupier tended to cut corners some what.