Introducing a small dog to a big new house?

Give him a tour of all the house, divided throughout a few days. Make sure to have treats or toys to reassure him with if he gets scared. My little terrier mix was afraid of my summer house(it was big too)I just stayed with him to walk through it and gave him treats throughout. Left little dog beds and toys in most of the rooms to make him feel at home. Perhaps you could try the same?