You will be better off having your fresh air coming from your basement. There's nothing wrong with that air, and its temperature is generally much more stable that the air outside. Your girls won't get frostbite in the winter when the light is off, and you won't be bringing in 100F degree hot air in July or August. My suggestion was to put a grill in the door that is the entrance to your closet as an air intake. Ideally that grill should be as low as possible (cold air sinks, hot air rises). Then have a fan pump air thru the filter and outside. This should be placed up as high as possible so that you catch the hot air.