PVC has limited heat tolerance, which is why it's limited to use on COLD water distribution.
CPVC had much higher heat tolerance, it's rated to handle hot water - but it might STILL be marginal at the temps that come out of most miners today.
4000 CFM is severe overkill for 5 Avalon 741 units - something in the 1000-1500 CFM range would be PLENTY, unless you plan to add a LOT MORE MINERS to that space.