Determining if current gas line is sufficient to run Tankless Water Heater

[clarehills]

Hi, I intend to install a Rennai Tankless Water Heater on the outside of my house. There is an existing gas outlet at the location that was probably put there to run a barbecue. It is a 3/4 inch line. How do I determine if the outlet has sufficient flow to run the water heater? Is there test/device I can use?
The heater requires 199,000 BTU
Thanks,
Clarehills

 

[Caduceus]

There's more to it than just using a device. First question is if it's natural gas or propane? You would need to know the total gas use of all gas appliances in your home (BTUs). You would then need to know the total length of all piping from the meter to the furthest appliance.
Then a manometer or gauge needs to be safely connected to test the pressure, measured in water column.
A pipe sizing chart is then used to determine what sizes the piping needs to be throughout the system.
Adding a 199,000 BTU appliance to an undersized piping arrangement could starve the tankless unit or another appliance of the needed gas to operate normally.
Natural gas is a safe energy source when installed and tested by a trained professional, but I'm reluctant to give any more advice than I have due to the risk of a little mistake or oversight turning into a dangerous situation.

 

[clarehills]

Caduceus!
Thanks very much for the reply! That is very helpful.
It is natural gas.
I can gather the pipe dimensions, lengths and junctions and the BTU needs of the other appliances.
It seems the best thing to do after that is hire a plumber to bring the manometer and make a recommendation on how to proceed.
This is a medium term (and part of a much bigger) project so I will post back as soon as the project moves along with an update
Thanks again,,
Clarehills