How much CO2 does a gas stove add to indoor air?

For fun I got a carbon dioxide (CO₂) meter. Standard atmosphere contains 400ppm of CO₂. Some studies suggest that mental performance begins to degrade when CO₂ concentration exceeds 1000ppm. I was surprised to see that when cooking on my gas stove (in the kitchen) the CO₂ meter in my office began to register levels approaching 2000ppm. I was curious to calculate how much CO₂ a simple gas burner adds to indoor air.

TL;DR: using a gas stove to boil a gallon of water in an airtight 30m³ room adds about 2200ppm of CO₂ to the air.

Detailed calculations:

It takes about 1,300kJ of energy to heat a gallon of water from room temperature (20°C) to just boiling (100°C). (Specific heat of water is 4.2 J/g/°C, a gallon of water weights 3.8kg, so we have 3.8kg * 80°C * 4.2kJ/kg°C = 1,300kJ. Note that this does not actually boil the water because it takes another 2.3 J/g to vaporize liquid water at 100°C.)

A gas stove is around 50% efficient in transferring heat to water in a pot, so we need to burn enough gas to produce 2,600kJ. Natural gas is mostly methane (CH₄), and 1 mole of methane releases 900kJ when burned with oxygen, so we're looking at burning 3 moles of methane. The combustion reaction is CH₄ + 2 O₂ -> CO₂ + 2 H₂O, so we get one mole of CO₂ per mole of methane burned.

At standard temperature and pressure 1 mole of gas occupies 22 liters. If the kitchen is 30 cubic meters = 30,000L then it contains 1,363mol of gas. Adding 3mol of CO₂ would roughly be adding 3/1,366 = 2200ppm CO₂ to the room. So it's easy to see how cooking with gas can markedly raise CO₂ levels throughout a house!

(Notes: For comparison, an average human at rest exhales about 11 moles of CO₂/day. Also, as noted in my previous post, a properly ventilated house exchanges air every 4 hours.)