Last two brews,

9.4L and 9.8L for a 90 minute boil in a 40cm pot

Thats Start of Boil Volume - End of Boil Volume, ie at 100C

or, and average of 9.6L over 90 mins...

6.4L/hr

I think I might call it 6.5L/hr

1. Your average internal kettle diameter and type. 80L Keg gas burner Diameter 40cm
2. How much wort you evaporated off during the boil. 6L/Hour
3. The duration of your boil. 90 minutes
4. Any notes on how confident you are of your figures. Average of 8 brews over one year.

1. Your average internal kettle diameter and type. 10L Birko Urn Diameter 24.5cm
2. How much wort you evaporated off during the boil. 3.25L/Hour
3. The duration of your boil. 1x 60 minutes, 1x 90 minutes
4. Any notes on how confident you are of your figures. Average of 2 brews. Birko is on flat chat with a fan to help control boil overs. Will be upgrading urn with a voltage regulator to control the boil better.

Buffalo Urn - 2.4kw electric element

38.3cm Diamater x 37.5cm Height

Brew indoors (Garage)

Mash Volume usually around 40 litres

Evap rate consistently 3.4 - 3.6L per hour over 10 brews. (5.4L over 90 min boil length)

Fact or fiction I think the size of the Power source be it Gas or electric affects Evap rate as there is a fixed amount of energy going into the liquid. My boil is constant but far from being "Vigorous" like you can get with a Gas rig. So in my case 2.4Kw of input energy is always constant, If I had a 3.6kw input in the same kettle I am 99% sure evap rate would be higher, same with Gas burner, bigger burner = more energy into the boil.

Some maths (which I dont understand) seems to back that up - https://au.answers.yahoo.com/question/i ... 351AAfaiUt

Nice stuff bundy! Let's do some maths...

BIABacus on your kettle estimates 4.93 litres/hour or 1.3 gal/hour.

Your actual is about 3.5 litres/hour or 0.925 gal/hr

The formula you have linked to would give us with a 2.4kW element...

2400/2256.4*60*60/1000=1.06364*60*60/1000=3.83 litres/hour or 1.01 gal/hour.

That's not a bad match for you.

If you had a 3.0kW element then...

3000/2256.4*60*60/1000=1.06364*60*60/1000=4.78 litres/hour or 1.263 gal/hour.

That's not a bad match for the BIABacus.

Obviously, this whole area is a complex one as ambient temperatures, humidity, wind, surface area, rheostat's etc, all come into play. My hope though with collecting more data is that we can come up with more and more accurate estimates based on surface area but I think these will hae to assume that you do have enough power to get a decent rolling boil going.

It's an interesting area and thanks for that formula bundy .