We do not recommend operating any of our ovens under a roof or covering as there is the potential for discoloration from the smoke on your ceiling surface. We've had customers who have installed a custom length chimney through a roof with great success. Unfortunately, we no longer offer chimney extensions or elbow joints. These parts will have to be sourced locally by the customer. If your oven was purchased prior to May 2020, it has a 14cm diameter chimney pipe. If your oven was after May 2020, it has 15cm diameter chimney pipe. As far as the oven's functionality any extra chimney exhaust pipe added above the damper control doesn't affect the oven's performance. In fact, this one of the ways they test units indoors at the Fontana Forni factory in Italy. The one other thing we'd strongly recommend is to check with your local building and fire codes for this sort of thing as these regulations vary from one location to another.