I just built a new house and went with the Water Furnace 7. I have an air return on the living space floor with a 30x30 filter there is also a filter inside the unit itself down in the basement. I have already replaced the filter in the return. Got a message later on my thermostat that said to replace filter. The filter in the return looks fine but the filter in the unit itself is dirty. I asked the salesman where to purchase the filter for the unit and he stated that since the return is filtered I do not need the filter in the unit, that it should have been removed when the unit was turned on. Does that sound correct to anyone? I would assume he knows but the filter is pretty dirty to not be needed. I am afraid to remove the filter if that dirty air is going to be going into the unit unfiltered? Any thoughts? Thanks in advance.