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Q: My husband is considering installing a vent-free gas fireplace in our living room. As a retired school teacher, I'm familiar with the effects of the CO2 gases exhaled by 40 students in a 1200 sq.ft. classroom. If we didn't open several windows top and bottom to provide fresh air inflow, symptoms of the beginning stages of CO2 poisoning (drowsiness, lethargy, etc.) would overcome my students and myself quite rapidly. Our living room is only 400 square feet, so I'm concerned about the CO2 emissions from the unvented fireplace. I asked a local fireplace salesman to compare the CO2 output of a 30,000 btu vent- free fireplace to the amount of CO2 exhaled by an average person, and he said he had no idea. Do you?
According to the Code of Federal Regulation - (Labor 29, 1900 - 1910.99), an average person at rest exhales around 5 liters of air each minute, and the exhaled gases contain CO2 at a partial pressure of approximately 40 mm Hg.. This calculates to slightly over half a cubic foot of CO2 being released every hour by the average human at rest.
Using this average, your 40 students were exhaling approximately 20 cubic feet of CO2 into your 1200 sq.ft. classroom every hour, or about 1/500th of the total breathing space volume.
A 30,000 btu/hr vent-free fireplace releases nearly 27 cubic feet of CO2 into the breathing space every hour, the equivalent of the amount of CO2
produced by 54 people at rest. Since your living room is only 1/3 the size of your classroom, the percentage of CO2 saturation would reach about
1/120th of the total volume of the breathing space during the first hour of operation, or over four times the saturation you experienced in your stuffy
classroom (imagine cramming 54 students into your living room! ). Exhaust from the second hour of operation would have an even more dramatic
effect on your air quality, as it would blend with the already-polluted results from the first hour, and so on.