In the past 5 years, I've lived in three houses. 1. 3500 sq ft , distinctly divided rooms, 2 story 2. 1000 sq ft open concept 20 ft vaulted ceilings 3. 1400 sq ft open concept in living/dining/den/kitchen 9 ft ceilings I've tested in all three, and gotten pretty much the same results. House 1 had to have a HT that went through the entire downstairs, 2 I wanted to see how the high ceilings did and this one, 3, it has to cover the entire house ( at least be able to smell it slightly when in the back bedroom and the tester ( a one cube melt .. .5 ounces ) is up front. BUT , after getting those results, I relied heavily on my human testers because all of their houses were different, and they had different things going on. Some didn't cook, Some cooked 3 times a day, some had pets and some didn't, some did power burns, others just let it melt and scent the room then turned it off to see how long the scent lingered.. etc.