I have found some plants that really help clean the air in the flat without costing me any money in energy to do so.
Of course you have to buy the plants, but after that outlay of cash you have some really clean air in the home for no money at all.
I have to water the plants, so if you count that as money then yes it does cost a trivial amount each month, but it is very minimal and it is also very easy to do. I water the plants once a week and they give me good air quality in my flat without having to run an air purifying machine to do so. I have about 15 plants in my flat and my flatmate also has a few, so needless to say we have a lot of greenery in the home and don’t have to worry about not seeing nature each day if we don’t get out. We have a good HVAC system when the weather gets hot or cold, so climate control is all covered in our flat along with the air quality. We won’t be running the system for another two months as it is now April and the weather is very mild and will be till the end of June. The local businesses will get busy soon and my cooling supplier is going to ask me to work more this summer to help with all of the a/c systems sales and service jobs from our huge customer base in town. Have a great summer!