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A furnace shouldn't be adding CO2 or CO to your air. Those combustion products should all be exhausted out of the house.

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Maybe this is something to have the landlord check? In practice I don't think most gas furnaces are as well sealed as advertised. Many years ago when I lived in a house with gas heat with a dodgy pilot light I got a pretty good feel for how the thing was put together and it was absolutely not hermetically sealed.

It's not supposed to be sealed, it's just supposed to have draft. (the flue always vacumming from convection)

> It's not supposed to be sealed, it's just supposed to have draft.

It depends on the model. High (>90%) efficiency, condensing furnaces are completely sealed off from the house: they take in air from the outside (via PVC pipe), combust, extract the heat, and exhaust the results (via PVC pipes).

* https://www.youtube.com/watch?v=lBVvnDfW2Xo

Older lower efficiency (<85-90%) furnaces suck in air from the house, exhaust into metal pipes (PVC would melt because not as much heat is extracted from the fumes), can be back-drafted and you have to worry about CO.

Basically: if the furnace has vents in which you can see a pilot light, it's the older style.

Out of the house and back in through the open windows?

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