> Can I replace a 25 amp single pole contactor on my heat
> pump with a 30 amp single pole contactor? Basically the same
> except for amp rating.
Yes -- with caveats, more is better.
Caveats:
(1) Coil voltage (control) must match exactly -- probably 24VAC on HVAC stuff.
(2) Max voltage rating of contacts should be at least as high as power you're switching, and preferably at least as high as the rating of the unit you're replacing.