Adding a vaulted vaulted ceiling will add extra volume, and change the internal surface area of the room it is located in. 

This will affect your heat load calculations, as the added volume will increase heat loss due to air change rates, and the added surface area will increase both losses and gains through the walls and ceilings. 

Here is a short video of me explaining vaulted ceiling design in h2x, ranging from simple, to more complex roof structures.