Without pulling my calculator out, the heater draws about 17a. The max you
are supposed to put on a 20a line when used continuously is 80% or 16a. So
just the heater is an overload. You can probably get away with it (my 23a
water heater was hooked up for 30 years with #12 wire until I happened to
notice and correct it) but I wouldn't recommend it.


120V, 20A = 2400 watts, x 80% = 1920Watts.
That's do-able, but not right. But
adding the fridge puts you over the top, so
you have to run a new line anyway.

Since this is a garage/workshop, it's not
possible to have too much power available,
so I'd spring for an extra $200 bucks,
and put in an 8-AWG 2-strand 240V cable
and a sub-panel, and a 50A 2-pole breaker.

Once you've gotten to needing to pull
wire, why screw around?