[TheForge] Burner "flares"?

[Gladish Family]

So, What does this translate into in terms of fuel consumption?
One of the reasons that I haven't set up a propane forge, despite having a
350 gal. tank, is that coal is much cheaper. The blown forges I've used are
a marvel of simplicity, but they sure go through the fuel. I'm thinking a
gallon an hour, though that might be a bit high.
The forge I'm working on is 7" x 18", heated volume, and I'm thinking I can
use one t-rex since I have no desire to try and weld in there. How much fuel
does one of these use?
Thanks,
Andy