Author: steveng There are a lot of variables that will affect your specific situation, such as the local climate conditions, where the boat is stored, whether or not your , and where you are measuring temperature, just to name a few. Your Xtreme Heater is designed to turn on at 40°F and off at 55°F, which should keep your engine compartment comfortably above freezing. If you notice temperature drops below 35°F, you should check to see if you are losing heat through vents or other air passageways. If you find that your boat’s engine compartment is well sealed from air loss, you should consider a larger or additional Xtreme Heater. Was this answer helpful ? Yes (0) / No (0) If my boat is on a lift, how do I determine which size Xtreme Heater is right for me? How long does it take to get hot?