Isotopes with low-lying long-lived isomers can behave very differently from other isotopes in astrophysical environments. In particular, the assumption of thermal equilibrium in computing the temperature-dependent β-decay rates of such isotopes can fail below certain temperatures. We focus on the β decay of Al26 since it is one of the most important isotopes in observational astrophysics and has a low-lying isomeric state; we compare and contrast these results with Cl34. We rule out recently reported Al26 effective β-decay rates that showed large differences from previous calculations, finding that we agree with the earlier results. We conclude that in general, effective β-decay rates should be defined separately for the ground and isomeric states at temperatures where thermal equilibrium cannot be achieved. © 2018 American Physical Society.