does a BC-36 superior wood burning fireplace need to be vented IF it is installed in an existing fireplace place opening with an existing chimney? The existing fireplace is too big so we want to use this product as an insert.. We want to install a gas log set into the superior unit and set unit in fireplace opening and finish off. We will not be using wood.Do we need to vent this unit if the chimney for the existing wood burning fireplace is intact and working?