City of San Antonio and plumbers follow the IPC book for all plumbing code guidelines. As some options provided here do not include the up to code recommendations, we highly recommend you consider adding these to your budget when scheduling your water heater install.
Drain valves for emptying shall be installed on the bottom of each tank-type water heater and hot water storage tank.
Water Heaters and storage tanks shall be located and connected so as to provide access for observation, maintenance, servicing and replacing.
Attics containing a water heater shall be provided with an opening and unobstructed passageway large enough to allow removal of the water heater. The passageway shall have continuous solid flooring not less than 24 inches in width.
An approved means, such as a vacuum relief valve installed in the cold water supply line above the top of the heater or tank, shall be provided to prevent siphoning of any storage water heater or tank.
Bottom fed water heaters and bottom fed tanks connected to water heaters shall have a vacuum relief valve installed. The vacuum relief valve shall comply with ANSI Z21.22.
https://up.codes/viewer/texas/ipc-2015/chapter/5/water-heaters#504.2
A water heater expansion tank is another small tank that is attached to the water supply pipe of the water heater. The expansion tank is designed to handle the thermal expansion of water as it heats up in the water heater, preventing excessive water pressure.
This is how the top of a gas water heater, up to code, should look like. It has the expansion tank, vacuum relief valve, and proper venting. Newer water heaters have sensitive sensors that will shut off your gas water heater if there is not proper venting or ventilation space.
Having a unit on the 2nd floor creates a greater liability during installation. The risks involved are much greater, and heavy work/lifting is required to complete the install. This is the reason for our added fee for any 2nd floor installations.