A 143,500 btuh fan assisted gas fired appliance is installed in a furnace room with a 61,400 btuh natural draft hot water heater. If the two horizontal ducts communicating with the outdoors are required, what is the minimum size of the combustion air ducts?

A 143,500 btuh fan assisted gas fired appliance is installed in a furnace room with a 61,400 btuh natural draft hot water heater. If the two horizontal ducts communicating with the outdoors are required, what is the minimum size of the combustion air ducts?