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I had my main vents upgraded 2 years ago and I believe they are Maid O Mist. I think the one closet to the boiler has failed already as it hisses the entire cycle. I am intrigued with the Big Mouth vents discussed on here and ready to order two if you can reassure me that they will fit on my system or let me know how to measure and purchase adapters. I have plenty of clearance in both locations (at least 6"). Thank you for your help.