New heat in the shop ..electric furnace help

Aluminum wire is used all the time for larger gauge circuits like ranges and electric furnaces. I'd bet most if not all available large gauge devices are rated for Cu and Al. All you really need to do is to use proper anti-ox "grease" and tighten them properly.

It does not hurt to check tightness after a few years. I've found a few Cu connections loose, as well as POS (Pacific whatever they are called) panels which are CRAP quality and which have POOR connections between breakers and the buss connection

The worst of these was one of our sheet metal guys when I was "in that" in the eighties. He had bought a 'then new' nice manufactured home.........hardly a trailer

This was "all electric" with electric heat, dryer, range, and water heater. So it "should have" been designed with adequate electrical in mind.

One of the large circuits (forget, dryer, range, furnace) was giving him fits. Turned out to be CRAP breakers (OEM) which DID NOT MAKE good contact at the buss.

Bear in mind this was "as built" and "nearly new." Bear in mind this was AFTER the aluminum trailer wiring debacle. Some of these panels should have resulted in federal criminal action.