Filtration is passive — air passes through a medium and particles are physically trapped. Purification is active, treating the air stream as it moves, which lets it act on things too small or too biological for a filter to hold, plus growth on wet surfaces inside the equipment. They solve different problems, so the honest answer is usually both rather than either.

Not necessarily. If your concern is dust, pollen, and dander, good filtration may be all you need — and it is the cheaper of the two. Purification earns its place when the problem is musty odour from the vents, microbial growth on the coil, or smells travelling between rooms. Those are the cases a filter cannot resolve however dense it is.

Because the evaporator coil is deliberately cold and wet — condensation on it is how your system removes humidity. In a Florida climate with near year-round runtime, that surface stays damp for months, and damp plus dark plus organic dust is how mould and bacteria establish. It is not a fault in your equipment; it is a consequence of what the equipment does here.

It depends on what you are trying to solve, and anyone who names one technology before asking about your property is selling rather than diagnosing. Coil irradiation targets growth on the coil. In-duct systems treat circulating air. Oxidation-based treatment is generally chosen where odour is the main complaint. We will match the approach to your problem and your existing equipment.

In-duct purification operates while the HVAC system runs, since it needs air moving past it to treat that air. In Florida that is most of the time, so the practical coverage is good. Coil treatment is a partial exception, as it acts on the surface rather than the air stream. If you want treatment during long idle periods, that is worth discussing before choosing a technology.

It treats the growth, but if the underlying dampness remains, conditions still favour regrowth. Lasting results usually need the moisture addressed too — humidity control, correct condensate drainage, and coil cleaning alongside purification. We would rather tell you that upfront than have you install one product and find the smell returns.