I have moisture on my windows in the winter months due to a tight house and no fresh air exchange. I can't afford a whole house solution now. A 20 year old stand alone dehumidifier that I borrowed to test removes lots of moisture in summer when the indoor temp is 76, but when the winter house temp goes below 70-71 degrees the coils freeze up. We keep the indoor temp at 68 in winter. Is that typical of these units, or is there something wrong with this one. Are new units better at indoor temps below 72 degrees?