When there isn't higher ambient temp, only 50 deg F, will it be able to heat a small attached hot tub?

Heat only systems can only air defrost and will need to shut down around 50 degrees ambient to avoid icing up. Heat/Cool systems (like the HE125TA) have hot gas defrost that allow them to operated into the mid/low 40's. It will heat a hot tub, but the unit becomes less efficient and will take longer to achieve the desired temps. There is no back-up heater in the heat pump. Normally we see that pools are typically shut down and winterized when the ambient temps begin to get down below 50 degrees... If you have any further questions please feel free to give us a call! Thanks.