Clock your gas meter. Shut down all other gas appliances, turn on that heater and time how long it takes the 1/2 dial, 1 or 2 cu ft dial to spin a complete revolution on your gas meter.
Google clocking a gas meter and you will see charts that will tell you btu per the dial you used.
Should be burning pretty close to those charts or you have an issue assuming you are not at altitude.
Guessing you are not very high in altitude from when I played your golf course this summer.
Good info, that..
We had Modine gas heaters at the old greenhouse my parents owned. I don't recall the size (btu rating) but two of 'em would heat a 24'X75' plastic covered hoop house fairly decently - and the insulation factor on those things is next to nothing - even with an air layer between.. IIRC, it was a one-inch line that fed 'em..
