Hot Water Heater Drip pan

[DD716TED]

I am planning on installing a drip pan under a new hot water heater that will be put in. I will be able to run the drain line from the pan directly down thru the floor to the crawl space. From there I will install a 90 degree elbow and a 4 ft section of pipe to take it thru the foundation air vent to the outdoors..QUESTION: To keep cold air and bugs out of the house, shouldn't some kind of check valve be installed in this line? If so, what kind?

[HayZee518]

depending on the size of the pipe, I'd pattern any kind of "check valve" after a dryer exhaust vent. In this case because of outside temperatures a mechanical metal valve won't do as it would freeze shut or open. I'm thinking along the lines of a tan latex sheet of some sorts like a flapper, fastened outside of the vent so its naturally closed, but opens when water comes down the tube. there will be some leaks past the flapper but the majority of air if there was a direct flow towards the flapper would shut it.