How do I model rooms with open doorways?

For open plan spaces where rooms do not have doors separating them, you will need to model it all as one large room.

 

Make sure that you set the room type to the one that has the highest air changes per hour (ACH).

If you need to use the wall between the rooms to place a radiator, then you can model these as separate rooms but make sure the room temperatures and the air changes are the same, again using the highest ACH. This will mean there will be no heat loss across that wall so the calculations are unaffected by modelling the wall.