This one has me baffled. In theory a house needs makeup air to replace the air removed by appliances. Also needed is fresh air to keep us from asphyxiation. Few houses have any specific source but we survive on leakage.

I had my house built pretty tight and there is a full set of exhausting devices.

Gas furnace
Gas water heater
Electric dryer vent
Cat latrine vent powered 24/7
Kitchen exhaust
1200 sf ranch plus full basement

Why are we still alive?