Water heater gas usage

[deep]

Hi can you please tell me how can i check that the water heater uses correct amount of gas ?

[Admin]

If you have a gas meter you can time how long it takes the slowest dial to make one revolution.  I attached a chart.  There will be a rating plate on the water heater that will tell you how many BTU's it is.  A tankless can be more complicated than a tank type as it's output will change depending on usage, so you need to open all the water taps to make sure it runs using the highest BTU's.