![](https://lemmy.kghorvath.com/pictrs/image/acc52990-8565-47d2-90e4-c42cb468c316.png)
You can, but the lower you go (usually starting around 30F), performance degrades, with around 15-17F being the lower limit that you can run it in heating mode and still pull heat out of the outside air.
Ideally your aux heat would only be needed on those more extreme days.
It defeats the purpose in the scenario that your vault is stolen and decrypted. But it still protects you in the much more likely scenario that a data breach exposes your password somewhere else.