Envirosept electronic air filters are a replacement for the normal disposable 1″ thick filter that is usually found in heating and air conditioning ducting. This is the best replacement air filter for the furnace that we sell and is why we give it a 5-star rating. It has a 5 year warranty (2 years total; but in the last 3 years the customer pays freight in both directions).
This filter opens like a 3-page book with the center being a metal grid and a filter pad on each side of the grid. The filter frame plugs into a regular 110 volt socket and has a built in transformer to bring the internal grid voltage down to 24 volts. The cord length is 6 feet and an extension cord can be used. The filter comes with 12 disposable filter pads.
Additional filters pads can be bought in a package of 12. They are ordered according to the size of the filter unit, but, of course, will actually measure less than the unit so that they can fit inside the frame and allow the frame to close. The unit holds 2 filters, 1 on each side of the electronic grid. The customer needs to determine when the filters need to be changed by visual monthly inspection. When one of them looks quite dirty, it is time to change them (usually every month or so).
One of the filters will be much dirtier than the other because the air goes through that filter first and deposits most of the dirt. That filter gets thrown out, and the cleaner filter (if the customer feels is not too dirty) should be taken outside and shaken gently to remove some of the larger particles. It then gets put in the first location and a new one placed in the second location.
During pollen season (fall and spring), it might be better if both filters were replaced at the same time. And if there are smokers in the house, both filters should be changed together.