I have a AprilAire #2210 Air Filtration system connected to my central AC unit in the attic (https://www.aprilaire.com/whole-house-products/air-purifiers/model-2210). I am trying to figure out how often I should change its chunky filter. Recommendation is 9-12 months, but is it 9-12 months of use? I only use this filter for AC and not for heating, so 9-12 months would be at least two summers of AC use - or 2 years. Or does this mean 9-12 months regardless of use, in which case I'd need to replace it before the summer since I installed it last June.
Lastly - the current filter has been there since last June (almost 1 year ago, but only used in AC season) and when I look at it now it looks very clean. Is that an indication of anything?
Thanks for bearing with me on this.