Keeping airflow exchanges going thru the rabbitry, even in wintertime New England is important. A “buttoned up” rabbitry in the winter can cause respiratory issues. During summer months we run a fan in the front louver from 8 am to 10 pm. In winter months we vent the front louver as needed. The back louver fan goes 24/7 except during continued extreme cold. I should note our rabbitry has heat that kicks on at 47 degrees. Heated or not, you do need some airflow.
Speaking of airflow, to keep odor down in litter pans or floor area, Odo-Ban works well. A gallon jug costs about $10.00 and goes a long way. You can find this at Lowe's or Home Depot in the household cleaner section. Dilute a few ounces in a large spray bottle of water. After emptying and hosing off a litter pan, let it air dry, then spray the pan before adding clean shavings.