I’m renovating my house in Thailand and one of my goals is to make the house more airtight. Better heat insulation cuts my energy bills, and it also separates the internal and external air, which means that the external air pollution can’t affect my house. Opening your windows to ventilate your house can sometimes do more harm than good, because it’s wrong to assume that the outside air is always better than the air inside your house.

The most popular air quality markers are CO2 and PM2.5, and the goal of a good ventilation system is keepling both of those measurements within a safe range.

If you want to have a safe level of CO2, you need to ventilate your house somehow. We’re all need to breathe and the act of breathing generates CO2 which needs to exit your house somehow. Disposing the old air isn’t that trivial, and you also need to replace is with the new air to keep your air pressure in balance, and the new air coming from the street can have an unsafe level of PM2.5 and other pollutants.

As you can see, CO2 and PM2.5 are slightly at odds, and excessive ventilation can also increase your energy bills, so it’s impossible to design a good ventilation system without measuring the air quality somehow. If your CO2 level is healthy, there aren’t any good reasons to ventilate your house, it’s just a waste of energy and money.

Measuring the air quality is tricky, since most air quality monitors are crap. I heard a lot of good things about Aranet4, but it’s pretty expensive, so I was looking for a cheaper alternative which can be as accurate as that product. A few days ago, I stumbled upon an AirGradient website, and the products listed there look too good to be true. I decided to order a pre-soldered kit and test its performance, and I hope I won’t be disappointed.