Changing out a water heater is simple, but making the initial installation is absolutely the most difficult part of the entire plumbing job. In order to do it correctly you must have a thorough intimate knowledge of not only the Plumbing Code, but the Mechanical Code, Gas Code and your local Fire Code. In many jurisdictions when we pull the plumbing permit we have to pull a seperate permit for the water heater and I can assure you, when the inspectors look at a new water heater installation they go over it with a fine tooth comb. You stated that the intended location has a floor drain, but is that in a basement, a utility room, a storage room, a garage or a carport? Because each of those locations have entirely different requirements. Is the proposed location a confined or unconfined space as specified in the code? What is the source of combustion air? Is that installation location shared with HVAC equipment? If so, the return air to the HVAC unit must be ducted in from outside the room. Are there other combustion appliances in the room such as but not limited to a furnace or laundry dryer? Will there be a horizontal run on the exhaust flue? If so, what is the height of the vertical flue? If it is in a garage or carport the base of the water heater must be elevated a minimum of 18" above the floor. You also stated that the floor drain discharges outside on the ground, but is that point of discharge 6-24" above grade and in plain sight or will it ultimately be concealed behind shrubs? The proposed location may not be in a bedroom, bathroom or a room which opens directly into a bedroom or bathroom. If the water heater is installed in a carport or garage you must have steel bollards or other suitable barriers to prevent contact with vehicles. Does you local code require seismic strapping? Can you use flex gas line? Maybe, but that is strictly up to your local code. You may be able to run the entire gas line with CSST gas line, but you will still be required to provide a shut off valve, drip stub and a union in the immediate vicinity of the gas burner, and the CSST may not be connected directly to the water heater. If your house is plumbed with PEX or CPVC many local codes require the first 5' from the water heater on both the hot & cold to be metal pipe (copper pipe, galvanized iron pipe or brass pipe) and you must have a union on both the hot & cold lines within 12" of the top of the heater. The drain pan must have a 3/4" drain line and it may discharge into the floor drain, however the lowest point of that line must remain a minimum of 2" above the flood level rim of the drain. You must also have a dedicated drain line from the T&P valve. The T&P valve MAY NOT discharge into the drip pan. The T&P valve drain line must also discharge into an approved indirect waste receptor or outdoors at least 6" but not more than 18" above grade in a conspicuous location. And from my experience, just when you think you have all of that figured out, the inspector will come up with some obscure local requirement you never heard of.

Bricks are the preferred material because they will not rot or rust if they get wet. The only code rules that you should be aware of is that both the Temperature & Pressure Relief Valve (T&P Valve) and the Pan must have a drain line to the exterior of the house or to an approved "indirect waste Receptor". The T&P valve MAY NOT discharge into the pan.

The vertical static head loss on the cold water riser is immediately offset by and equal and opposite gain in the drop on the hot water side, therefore the actual gain in vertical head pressure loss is zero. With an 18" increase in elevation the combined total additional pipe length is 18"x2=36" or 3'. For 3/4" copper pipe the additional friction loss at a flow rate of 1gpm would then be 0.003psi and in a worst case scenario, at 10gpm the additional friction loss would be 0.024psi which is hardly enough to even be perceivable on a standard pressure gage. It is far more likely that some sediments were stirred up during the change out and have now obstructed the screens in the Kitchen faucet & lavatory faucet aerators, washing machine line screens, the shower head flow restrictor or water ports and possibly in the toilet fill valve orifices. The solution would be to remove the aerators and washing machine feed lines and clean the screens. then disconnect the shower head and clean the flow restrictor or water ports and finally, if necessary disassble the toilet fill valves and either clean the orifices or change the diaphrams.

The preferred method is to run the line through the wall and discharge outside the structure. When discharging outside the structure the point of discharge must be at a clearly visible location and may not be obstructed by shrubbery or landscaping materials. When discharging outdoors the discharge end of the pipe MUST BE pointed downward. Under the International Residential Code the point of discharge must be within 6" of the average terrain ground level. Under the Uniform Plumbing Code the point of discharge must be greater than 6" but not more than 24" above average terrain. In a garage or unfinished basement the T&P line may discharge on the floor providing the said floor is equipped with a floor drain. When discharging on a floor the T&P line must extend from the output port of the valve to within 6" of the floor surface and the end of the line must direct the flow downward. When a gas water heater is installed in a basement where a T&P gravity flow drain line cannot be achieved the standard Temperature & Pressure Relief Valve (T&P) valve is to be removed and a WATTS 210 gas shutoff valve installed on the water heater vessel. A Pressure Relief valve is then installed on a hot water line at any convenient point above grade and a discharge line extended outdoors or to an approved indirect waste receptor. The T&P valve may be discharged into the house DWV system providing it is connected by means of an approved "indirect waste receptor" such as a utility sink or floor drain providing the lowest point of the discharge line must remain a minimum of 4 times the discharge line diameter or 2", whichever is greater, above the flood level rim of the receptor. A T&P discharge line SHALL NOT discharge into a water heater drip pan. The T&P discharge line diameter must be equal to or greater than the diameter of the discharge port. If the total developed length of the T&P discharge line exceeds 40 feet, the line size must be increased by one nominal trade size. All horizontal runs of the discharge line must be pitched at 1/4" per foot towards the discharge end. There shall be no traps or valves on the discharge line and the discharge end of the line SHALL NOT be threaded. (If run with galvanized iron pipe the threads must be cut off the end of the line).