Easier to boil then no chill some water in a cube then bring it down to 4°C in the fridge, then add it to the boiled wort. Much easier than handling big chinks of ice that are potentially unclean and unsealed.
Have done it before when using the 19L pot.
- boil then no chill water
- let cool to ambient
- in fridge overnight to bring it down to 4°C
- brew day, boiled wort transfer to fermentor (avoid HSA)
- add chilled pasteurised water
Use this,
www.onlineconversion.com/mixing_water.htm, plug in your volumes and temps (assume your boiled wort is about 93°C once off the boil)
example 10L of 93°C wort + 13L of 4°C water = 23L of 42.69°C wort.
It won't bring it down to pitching temps immediately, but it will bring it down past isomerisation temps. A few more hours in the fermenting fridge will bring it down to pitching temps ok. Keep it sealed in that time and there isn't much risk.