Enclosure Error- Operation would result in non-manifold bodies
 

I am currently modelling a geothermal earth air heat exchanger entering a room (a box). There is then a vent on the other side of the room that is attached to a solar chimney which will accelerate the air out the house.

I have modelled so far in design modeller the house attached to geothermal pipes. I was looking to test a simulation at this stage but have come across the enclosure error.

As I am modelling the heat transfer to the air through the pipes and then the mixing in the room I need to create an enclosure as a fluid domain. I was hoping to then do a boolean subtraction to leave me with the domain of air to be meshed.

Any advise on how to proceed would be appreciated!