Gas usage without using anything?

My family just moved into this new duplex, we live in one part and the other part is currently empty, there are separate gas and electric meters for each part of the house. We haven't use any gas appliances in the other part of the house, but we are still getting a gas usage of 5 therms on the bill. I know it's not a lot of money but I am just wondering why is there gas usage when we haven't used anything related to gas.