I recently cleaned our air ducts and added a UV light filtration system to our house. I think it definitely improved indoor air quality. I even let the fan run for 2 hours during midday. So far, less sinus issues (probably my recent diet changes help this as well) and when I walk in the house, the house doesn’t smell any, even after cooking some strong foods. The real test will be during the spring season when everything blooms. My sinus allergies typically flare up during that time. I’m hoping this will help reduce that issue. Overall, I think it was a great investment ($650 for duct cleaning and UV light installation). I’m not an expert in this, but my guess is that if you have one of these, it should be helpful: 

• Many carpeted areas
• Family member with asthma
• Young toddlers near floors
• If you see a lot of dust settling in the house

For the last few years, many of us spent a lot of time in the house.  Buyers have been looking for bigger homes as well, needing office space, work-out/play room, etc.  So, indoor air quality is more important than before.  
I made a video about changing the furnace filters in the two air intake points and UV light treatment system in the ducts according to my HVAC guy.  I’ll report back after the spring allergy season in a few months.