What an Action Day Is
Through winter, Utah's Division of Air Quality watches particulate levels trapped by valley inversions and calls a daily designation. On a Red day along the Wasatch Front, solid-fuel burning is restricted—and those days fall in the middle of heating season, which is exactly when you'd want the fire.
What Still Runs
Sealed gas units and electric units are unaffected. That's the practical reason gas became the default hearth in Utah's valleys: it works on the days you most want heat, and it adds no smoke to a basin already managing its own air.
What Doesn't
Uncertified stoves and open fireplaces can't be used. EPA-certified stoves registered as a home's sole source of heat can keep burning—but that exemption generally requires the stove to be your only heat source, not a supplement alongside a furnace. If wood is your backup plan rather than your primary, it likely doesn't cover you.
If You Live Above the Inversion
Canyon and mountain properties sit in a different situation, and the calculation flips: cold is harder, outages are more likely, and wood earns its place. Same state, opposite answer—which is the whole reason this site starts with where you live.