There are different types of air exchangers. ERVs transfer moisture from the wet air stream to the dry air stream. They tend to retain moisture in the home while ventilating. HRVs do not transfer moisture and are better at removing moisture. Either kind must be operated on "high speed" continously until the home is dry. This could take month. Check for clean air filters and and dirty heat exchanger which slow air flow. Cracking windows high and low encourages air change, drying quicker and may help initially. Grasshopper loves dehumidifiers, but with cold windows near freezing require very dry air with a near freezing (32^F) dew point. Dehumidifiers dry down to 40^F dewpoint. This not low enough for cold climates window drying. Outside air is 20^F dewpoint when there is a heavy frost. Heating outside air and ventilating it is cheaper than dehumidifying and more effective. Make sure there isn't a water leak some place.