You can find the Catholic position on this issue on comment #13
I still cannot see the issue: Either the waste gases go up through a stack, or they go through a bundle of tubes, then up a stack. The cremation chamber is the same. The body is treated EXACTLY the same. Only the resulting gas stream is affected momentarily as it passes through a heat exchanger.
It’s like adding a catalytic converter to the exhaust of your car. The fumes end up in the same spot, only very slightly delayed. Besides which, when I was doing my Catechism, I seem to remember cremation being frowned upon, so how would this affect most practicing Catholics anyway?