Coast Guard Auxiliary Flotilla 29 on Lake Lanier Gainesville Georgia: – The Boat: 24-foot fiberglass deck boat with boat cover on and vents blocked to prevent heat loss! We placed a furniture cover around the engine compartment to insulate. – Record Setting Low Temperatures: 6-8 Degrees F – Lake water temperature was a constant 48 degrees (ACOE) – Boat is a wet slip (sitting in the water for this test) – Single engine big Bravo 3 Merc I/O with one 600 watt Living on Lake Lanier, we have what is known as a warm lake effect, that being the actual air temperature was only 6 above in Gainesville Georgia however the air temperature at the boat was 2 degrees warmer (as in 8 degrees at 6:00 am listed above). Notice the average engine room temperature was holding at an average of 39.88 degrees for this test. However the majority of the time the engine compartment stayed at 40 degrees. There was some thought whether a second heater would be better, I would hold off and continue to use one 600 watt unit. Would I purchase another Xtreme heater? You bet, in a heartbeat! This is the bilge heater you want, Its Coast Guard Approved and it works! Chuck Kelemen Being able to mount the Xtreme Heater in any orientation really made a difference for my install. Nothing but the best for my baby!