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D-1 venturi's cant be closed. They are always on. The tub does have a circ pump (unless its an @home).Their cover does not have what I call a linear heat seal along the seam. many tubs do not.I am blown away how many covers do not have foam along the seam. Most Canadian manufacturer's do (Hydropool, Beachcomber, Arctic) and some American made ones do too like Coleman. If you tub does have the seal and I didnt mention it, please add to my list.
HotTubman you know so much about so many brands I envy you. I really wish you still sold Coleman Spas cuz you were such a great voice for them. Are you working today while us Yanks are eating, drinking, napping, and watching football, at least at my house we are. LOL