Rulew of thumb DC vs AC coils

Hello, and I'm unaware of any rule-of-thumb. A web search reveals there's info out there on operating AC relays on DC and vice-versa. A relay designed to operate on 24 VAC will probably work OK on 24 VDC (or even less voltage). If you have the relay and an adjustable DC power supply capable of supplying the requisite current, that would be a safe way to proceed as you wouldn't want the relay coil to overheat (assuming the switching application via relay isn't just momentary contact). Sincerely,

If the relay coil depends on its AC inductance to limit current through it, any DC usage may damage it. Or perhaps it may operate on a low DC voltage (but with a comparatively high current draw).

If the coil is mostly resistive at the design frequency, DC at a similar voltage should be OK.

I will GUESS that whatever DC voltage results in the same current draw as its

Don't forget if operating the coil with semiconductors, switching off the coil's current is likely to produce a damaging voltage spike. A reversed biased rectifier across the coil will shunt that.