"I have allergies. Sometimes I get headaches and feel sick. The air in my house smells stale."
Is it you or your house? I can measure the humidity level in your house and look for sources of moisture, which may be contributing to mold growth. Do you have a fireplace? Negative air pressures in your house may be dragging carbon monoxide back into your house. I always test what carbon monoxide levels are occurring in the house, and whether they are coming from your furnace, hot water heater, or fireplace, etc.