My big problem right now is adding a filtered fresh-air intake to my house. CO2 in my rooms spikes when working at home and above 600 is cognitive impairment and you definitely feel it (I'm pretty sure meetings which go off the rails at work have this problem too - I really need a wearable monitor so I can cancel them when it starts happening).

The thing is I also need to do heat recovery, and since it's Australia, I definitely want to be able to do a filtered air overpressure in winter.