Several of the portable hot tubs have a limit to the outside temperature the unit can be used in (40-50 degrees), is there a limit to this model/brand?

Hello Noelle and thank you for your question. For the Alpine model, the recommended operating temperature is 40 degrees Fahrenheit and above. We do have one inflatable that the manufacturer claims works well all year round. It is the Spa-2-Go http://www.spasandstuff.com/spa-2-go.html