Good New Year to all who have helped me over the years, those to come!

[torchkeeper]

My 12 year old Bosch/Takagi was moved to new home on same lot . Right on shore of Lake Ontario. Exhaust was on leeward side, 12 years no problem ever. The recent sub-zero winds off lake 30 degrees below F.  Wind came in exhaust with factory hood. Bought a new 199,999 btu. A.O. Smith/ Takagi 540-t-h3 indoor model. It has electric heating blocks that come on when otdoor tepm reaches 36 drgrees f. They also sell a backflow preventer , to control wind flow back into heat exchanger. Question is has anyone installed one of these backflow preventers? Seems it is 4 inch but exhaust is 3 inch pvc. You have to tap in a 3 inch pvc coupler directly into heater. the guys at the plumbing supply house have yet to sell one! They seem to think it is nova-vent . I don`t want a new freeze-up situation. What is everyones opinion?

Thanks as always !