ayman Alkhoder wrote on 02 June 2000 at 12:02 PM: For small domestic water heater. What will be the minimum size for the vent pipe from hot water line. This vent pipe is used to relive built up pressure in the hater and prvent bursting.
What the HELL are you asking? Vent like in Flue piping can be as small as 3″ BUT I never use less than 4″
If your talking protecting the tank from excessive Temperature (210 Degrees F.) Or excessive Pressure (150 PSI) and YOUR asking ASME section IV code (American society Of Mechanical Engineers) Your APPROVED min. would be a 3/4 inlet and 3/4 Out let WITH an approved means of testing the bloody thing.
Then of course YOU do know that some codes also require an ANTI Vacuum type protection also. Some codes even require a “relief” valve on the cold water piping leading to this heater with a means of protection for expansion and contraction to prevent undue stress on the near heater piping.
Did you bother to investigate were the discharge piping is to terminate from the T&P “RELIEF” valve? What provisions are you allowing to prevent excessive water temperature from entering the drainage system as per MOST codes. Are you going to elevate this tank as per most manufacturers recommendations using the NFPA type of appoval?
Did you size in developed lenth the size of your gas supply piping allowing for drip legs if required?
Are you concerned about “Venting” the hot water piping itself like we do on hydronic air handler coils? When you asked min are you asking the ASME or AGA which is much more conserative? Have a great week end