When I think about when I have mine off heat completely in below freezing temps I think of about 9weeks. Knowing your temps are going down to freezing, if it's not a big deal to use the heat for a bit longer, then you're playing it safe. In just a few more weeks there will be no question that you're good to go. I have same temps where I am but it's super wet cold as opposed to dry so I tend to go longer than if I was in a dry climate.