First run using LPG - a question

[Glyn]

Tomorrow will be my first run using LPG. Until now I've been an internal electric element (2kW) but am wanting more control for my spirit runs.
My pot is a 50L stainless keg.

Tomorrows run will be a stripping run with my pot still head. Planning on having a play around to get used to the gas...

My question comes when it's time to do a spirit run.

How do you know how much heat you're pumping in?
Obviously I can see the flame if I bend down, i can see it getting bigger and smaller as I turn the gas up and down.

But what does a 1kW flame look like?
What about a 750W flame? and a 1.5kW flame?

I could measure output from the still and calculate heat input from there (presuming I knew the reflux ratio) to get a gauge for things. Is this how everyone else has done it?

Cheers