HRV technology works, and while there are a few possible causes behind your trouble, most are easily fixed. If you have a furnace, it’s possible that it has a humidifier that’s pumping too much moisture into the air. Depending on window design and insulation values of the glass panes themselves, it’s often necessary to set interior humidity levels dryer than ideal for comfort during winter, in order to eliminate window condensation. It’s also possible that the balancing flaps, fan speed or controls of your HRV aren’t set properly. To operate effectively, every HRV needs to move a balance of air into and out of your home. Though not likely, another possible cause is faulty HRV selection or installation. If the unit doesn’t move enough air for the size of your home, or it was connected improperly when it went in, poor performance could result. If wet windows persist after turning your humidifier off, have a heating and ventilation specialist inspect your HRV for proper installation and set-up.