What size Kettles?

[Ozbrewer]

I'm in the process of a very (very) slow electric brewery build. I have all the bits for my control panel, but was thinking of buying the kettles next. I'm going to go the stainless steel kettles from the German ebay crowd, Bergland (catering-supplies) I think.

So, I'm undecided between the 100lt or the 70lt kettles for all functions, or if I should go 100lt for the BK and then the 70lt for the HLT and MLT. I will be going camco 5500w elements.

I ferment in 33lt HB buckets. Currently my boil kettle is a Youngs 33lt bucket with element. I normally fill to 29/30lt mark, and volume into the fermenter after boil and cooling is 26lt - according to scale on the fermenting bucket. This volume gives me enough to fill 30 x 750ml bottles and 2 x 500ml bottles per brew.

For the new setup, I want to be able to brew double batches, so looking for at least 54lts or more into the fermenters, which probably means about 60lts or more pre boil. 

I presume the 70lt kettles be ok for this volume given likely boil vigour and boil off rates or would it be better to go to 100lt kettles? Interested in anyone who is brewing to these volumes.

[Hop Bomb]

Ive had a pre boil volume of 48 litres in my 50l keggle & with no issues. I watched it carefully as it got up to full boil & then rolled off the gas a bit to prevent any boil over. Id say with 10 litres head space in your BK you'd have no worries at all.

[Ozbrewer]

Thanks Hop Bomb. Nice and easy answer. I think I will go the 70lt ones then. I still want to be able to do single batches and I think the 100lt pots might mean my minimum brew amount is too large for what I want.