Boil off rate

[RedmondUK]

Planning on building a herms system with 70 litre pots and I'm curious to what the boil off rate would likely be. The kettle diameter is 45cm 18". The kettle I am currently using has a diameter of 38cm 15" and my boil off rate is typically 4 l/h 1G/hour.
Just wondering what boil off rates people are seeing on a similar sized kettle.

Thanks for any info in advance 👍

 

[doug293cz]

good first estimate might be (18/15)^2 * 4 = ~5.75 l/hr/

Brew on