Before rushing out and purchasing the latest home humidifier, it is always best to gather information from an experienced heating contractor with knowledge in ventilation. In many cases the humidifier is not the correct option for the source of your indoor air quality concern.
Humidity levels inside the home should be between 30-50%. The majority of homes with central heating and cooling systems will maintain ideal humidity levels, without a humidifier. During the cooling process, air conditioners and heat pumps are removing moisture from the air. As the air passes over the evaporator coil it absorbs heat and cools the air. At the same time, moisture in the air condenses on the coil and is drained away. A well maintained, efficient HVAC system can help keep relative humidity levels between 30-50%.
Other draw backs to keep in mind, is that too much humidity will cause mold and bacterial growth. Humidifiers can cause excess moisture. Air that is especially humid is heavy and can make it hard to breathe.
Maintenance on humidifiers is a must! With water, can come mold and mineral build up. Especially in the Vancouver/Portland area, the tap water has heavy mineral deposits. Some models require semi annual maintenance, and without it you will be creating a breeding ground for bacteria and mold.
If your humidity levels are not in the normal range, another option to consider is an Energy Recovery Ventilator. Not only does it control heat like a Heat Recovery Ventilator system does, but it also controls humidity. It takes the humidity out of the outgoing air and puts it into the incoming air.