This has to come, from what your place is made of or where it stands, as aritmo mentioned in his bad cleanup situation he found. In LV chances are it is various formaldehyde outgassers. The main ones are UFFI = Urea Formaldehyde Foam Insulation and numerous plastics made with phenol and formaldehyde. https://en.wikipedia.org/wiki/Urea-formaldehyde UFFI is a prolific outgasser of formaldehyde because of 3 reasons, 1 -…
They added vinyl flooring and new appliances right before I moved in. I’m unsure about foam but I can ask. This building is from the 90s if I remember correctly. Is 300ppb considered low? I am currently keeping the levels below 150ppb by keeping the windows all wide open which is difficult for long with the desert heat.
Get a counter current air exchanger. It vents cool inside air to the outside along a heat conducting surface that contacts the hot outside air to the inside, with only 5-8% heat import.
Here are some explainers as well as some DIY methods.
https://www.youtube.com/results?search_query=make+counter+cu...