I'd really appreciate some help here. I recently bought and moved into a house with a 10'x10' heated crawl space under an addition to the house. As the weather turned, we had some mice move in and I located their entry point to the crawl space, which had easy access from the outside and the inside giving them somewhat of a red carpet into the house. Part of the problem was that whomever did the HVAC didn't use a collar for the ducting entry, so there was a wide open path for mice into the house. I suspect much of the work was done DIY, based on other things I've seen.
I've completely sealed the crawl space, which leads me here for your help. The crawl space is heated via a duct from the furnace. However, there is no return air in the crawl space. Previously, there were enough cracks into the house and to the exterior to give the air somewhere to go. Now that I've sealed it, do I need to put in a cold air return as well? Or would a vent to the outside work?
More information about the crawl space: 10'x10', floor is dirt, covered with poly vapor barrier and gravel. Walls are concrete and insulated with pink styrofoam. Rim joists are insulated with batt insulation and covered with poly vapor barrier. Ceiling (floor of addition) is uninsulated.
I live in a cold climate, down to -25F in the winter.
Thank you for your time!