Is there a way to plug a 6-20p 208/220/250v plug into a 10-30r receptacle? I can't seem to find an adapter for this. I bought a 220v fahrenheat heater and want to be able to plug it into a range or dryer receptacle.
You will not find a legal or listed "adapter" for this.
A 6-20 is a straight 240V grounding 20A device. A 10-30 is a 120/240V non-grounding 30A device, where the grounding function is provided via the neutral. This is only allowed in older range and dryer circuits, so any adapter would not be legal to use on any other circuit.