I have an S9 running as a space heater. It's a lot quieter after upgrading the fans, but that's an additional expense. The PSU fan is the loudest, and cheaper to replace. I use the Braiins firmware which allows me to set a target wattage. They run a little more efficiently at a lower wattage too.

It's unlikely to be "profitable" but use the waste heat and consider that you're paying the full price for non-KYC Bitcoin I stead of giving up your privacy for a discount.