Tbh i am a total newbie to this. I think it has to be hot smoke because the box will be where the flues are rising from the 3 appliances. There isnt relly space to put enough pipe in for cooling.
I hadnt thought about using the flues separately but a damper on each one looks like a necessity and would also give that option.
Obviously i need to look at temperatures now!
Thank you so much for your reply its very helpful. 🙏