I have an air things air quality monitor. It is showing peaks of CO2 and VOC's at various times. We just replaced our furnace and hot water tank. The old ones were atmospheric vented, now each have their own air supply from outside. We also have a couple sealed gas fireplaces. In the graphs Nov 4 was the replacement date but you can see the numbers are improving but still not great. I want to more carefully check the new and old equipment for leaks of exhaust and methane as I can't explain the peaks and valleys especially well. Can anyone recommend inexpensive & relatively reliable gear for this task? There are cheap solutions on Aliexpress for $40 to $80 and more. There are single function devices available at princess for $100-$150. and probably better gear for a lot more from specialist sources... I don't want an alarm. I'd like some sort of "sniffer" that I can check equipment, furniture, rugs, etc.

