We've had an air exchange added to our hot air furnace as well as an air cleaner that replaced a single 1 inch pleated filter. The TVOC and general air quality has improved considerably. At first the filters on the air exchanger were dirty after one month, now we're able to let them go much longer before replacing. It seems we had a lot of dirt in the duct work even though we'd paid to have the ducts cleaned. Now the concern is humidity. Our house has never gone above 25% humidity and regularly is at about 20%. We both have allergies and I have chronic sinusitis so those humidity levels aren't acceptable. I have a room humidifier in the shop that helps with static electricity and recently have been using that in our bedroom. It still only reaches 26%. I have a whole house humidifier on order from our HVAC company and plan on setting it at 35% during the winter unless we go below zero for too long. I'm wondering how you handle humidity in your home in the winter, esp. those living in the northern states?