Ask your plumber and also the building inspector department. The plumber has guidelines and the building inspectors probably have hard and fast rules they follow.

Gas service capability is complicated because it depends on line size, pressure, and various other factors, and some are configurable by the gas company. You need to talk to the gas company or an experienced plumber to determine if there is a relatively simple way to get the service you need. If you are relying on the guy from the city, he may not really understand the alternatives.

For example, they may deliver 2 psi gas at the street, but drop it to .5 psi for residential service, and then further limit the flow by using a smaller capacity meter. Asking them to swap out a pressure regulator or meter might allow higher flow and/or support for higher BTU.

Bruce

I am curious how you were able to determine your current gas line can deliver the equivalent of 350K BTUs. Was this calculated based on the pipe length and diameter and static pressure, or it is a number the gas company quoted?

I think Bruce is correct. The gas utility can make a call to your home and perform a pressure check. My utility PNG will perform this test at no charge. I would call your utility and request to speak to a technical specialist about your existing situation and what you propose to add. Of course all these appliances will not be operating at same time.

IMO