We have a Grand Banks 36 with single Cummins Turbo and have installed a "Heater Craft" unit under the steps to the front cabin. It is higher than the top of the engine and has not presented any problems with air locks. It is a remarkable heater. In the Pacific Northwest there are a lot of times that some auxillary heat is very welcome. We got their largest model and ran ducts to the lower helm station and front and aft cabins. With flexible 3" duct it was relatively easy to get the air ducted, a little more work to get the plumbing done. Our installer chose to place the unit outside the engine room to eliminate fumes and odors from the engine room being pumped into the cabin. The alternative would be to duct the intake air from the cabin down to the heater in the engine room. Steve Wyatt "Magic Carpet" Anacortes, WA