SW2Fiddler
We Are Cognitive Dissidents
The 1" conduit is in place.#6 is 75A at 90 degC, which derates to 60A ampacity per 310.15(B)(3)(a). #14 is 25A at 90 degC, which derates to 20A. 75 degC termination ratings apply at the breaker and appliance terminals, but that's 65A for #6 and 20A for #14 (310.15(B)(16)).
1" provides plenty of space; it's the minimum size for 3x#6 (HPWC) + 2x#14 (120V) + 1x#10 (ground). If you only pull hots for the 60A circuit (and no neutral), you can even use a 3/4" conduit.
You may share a single ground (not neutral!) but it must be sized for the largest circuit. 60A requires #10 ground.
I would pull up to #3 gauge (and appropriate ground, no neutral) for the HPWC, and #14 for the 20A. Question was about the derating due to the multiple circuits in the same single 1" conduit. Don't we hit a limit before the 100A level, because of the second circuit?
And I am getting all electrical work permitted and inspected, even though this stance is severely delaying my kitchen remodel!
Rick