Have you tried the new Whirlpool Air Purifiers? They are hepa rated and I recently tried out their 2-in-1 filter. It saves me time and money from buying a HEPA filter and the pre-filters separately. Plus it's easy to change, I just take out the front and pop in the 2-in1 filter. I'm amazed how it works with my allergens (pollen) and the dust around my house. (I have two small dogs as well, so it helps with the pet dander as well).

I keep it in my bedroom since I like to have it on when I go to sleep. I do set a timer on it because I'm a deep sleeper. It covers my entire room and it pretty quiet even on the highest setting. It states that it covers an estimated room size of 508 square feet on Amazon.

Does his doctor recommend this? Mine said it would be a waste of time. She said it was more important to keep the humidity between 40% and 60% (via humidifiers or air conditioning depending on season) and use supplemental oxygen as needed.

However, he should absolutely get one if there is a smoke or other serious air pollution issue where he is. You can check his area's air quality (AQI) at any weather site.

A friend works in the industry and lives in a wildfire area. He says you basically get what you pay for, and recommends this Whirlpool .

But again, check with his doctor first so you don't waste the money. A good vacuum cleaner (with HEPA filter) and regular dusting will probably help just as much.