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Vent Free Gas Fireplaces:
How Much CO
2 Is Too Much?

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?

Sweepy  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.

Sound kind of oppressive? It gets worse: don't forget that the flames from the vent-free fireplace would be consuming oxygen from the room at the same time, while lacing your remaining air with other nasty substances like carbon monoxide and nitrogen dioxide.

A fireplace is an easy place to install a vented gas insert, since it already has a chimney extending through the roof. A typical co-linear vent kit for a 15' fireplace flue only costs around $300.00, and improves the room air quality in two ways, by drawing combustion air down the chimney instead of from the room PLUS venting the gas exhaust up the chimney and out of your breathing space.


Read about a recent study of the effects of long-term exposure to CO gases

Read about respiratory irritation from vent-free exhaust in the breathing space

Read a posting about vent-free gas appliances from an indoor air quality scientist

Read what Consumer Reports Magazine has to say about vent-free products

Read letters in defense of vent-free products

Read our opinion about vent-free gas appliances

Read about a 2016 ASHRAE standard that could eliminate the entire vent-free product category in the US

Have a vent-free experience you'd like to report?  Here's a link to the Consumer Product Safety Commission website.

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