With the popularity of gas logs and fireplaces most new homes no longer have wood-burning fireplaces installed. Though there are still a few of us who enjoy cutting and hauling wood, most people enjoy the conveniences of gas logs and fireplaces. With no mess, little maintenance, minor heat loss, and easy installation, gas fireplaces are ambience at the flick of a switch. Its no wonder people are lining-up to add these benefits to their home.
Fireplaces vary in design and efficiency but all indoor fires hold the same considerations. Fireplaces convert fuel to heat while emitting some amount of byproduct. Gas fireplaces can burn for far longer periods nonstop and with greater veracity. This makes gas fireplaces and logs more susceptible to some hazards than wood fireplaces.
Fireplaces convert fuel to heat by pulling in air for combustion. A fireplace that pulls combustion air from the house can depressurize a well-sealed house. Fireplaces, dryers, bathroom fans, kitchen exhausts, furnaces, and water heaters all work to depressurize a modern home. An external combustion air source or keeping a window open can be important when using a fireplace in a well-sealed room. Especially true for modern homes, retrofitted and non-vented gas fireplaces can be a hazard to indoor air quality. Fireplaces that pull combustion air from a room are also pulling the houses warm air with it. This causes heat loss as well as depletion of oxygen.
After the fuel is burned there are several ways fireplaces release emissions into the air: A chimney releases the fires byproduct up into the air and above the house. Direct-vent fireplaces have flues at the rear of the firebox allowing byproduct to escape out the back of the fireplace.
A vent-less fireplace has no external exhaust (no flue or chimney) for the by-products and contaminants to leave the home. Vent-less fireplaces should be maintained once a year and run at only a few hours at a time. The ‘Oxygen Detection Safety pilot’ system makes a vent-less fireplace acceptable. The ODS automatically shuts off the gas supply in the event oxygen in the room falls below 18%. The ODS doesn’t monitor pollutants and water vapor, which may also be in the air. Manufacturers of vent-less fireplaces state that the levels of emission are low and within the current national standards and guidelines for indoor air quality. However, according to Frances Dougherty Jr. at the Environmental Protection Agency there are no current national standards for residential indoor air quality.
Several gases that are emitted from burning a gas fireplace are:
- Water vapor makes up about 60% of the output of a natural-gas fire. The American Gas Association estimates that 28,000 Btu/hour vent free gas can produce 4.6 gallons of water vapor a day. Increased levels of water vapor can help increase mold growth. The EPA recommends indoor humidity be below 60%.
- Carbon dioxide makes up to 40% of gas combustion by-product. CO2 can raise a person’s breathing rate and cause minor eye irritations and is a health hazard at high levels. The US Public Health Service’s carbon dioxide standard is 600 parts per million in schools.
- Carbon monoxide can cause death. CO can be produced if the air to gas ratio is not balanced. A gas-fire with a yellow tipped flame can be an indication of maladjustment and increased pollutant emissions. The EPA standard for outdoor levels of CO is 9 parts per million. OSHA’s and the EPA’s acceptable levels of CO in schools are 35 to 50 parts per million.
- Nitrogen dioxide is a corrosive oxidant gas. The EPA states that NO2 irritates the mucous membranes in the eye, nose and throat and causes shortness of breath after exposure to high concentrations. There is evidence that high concentrations or continued exposure to low levels of nitrogen dioxide increases the risk of respiratory infection and that repeated exposures may lead to the development of lung disease such as emphysema.
Sensors that can detect CO, CO2 and NO2 are a good investment. Without a national standard for residential indoor air quality these detectors can help prevent potential health risks.
Gas logs and fireplaces in older homes have become common and do not necessarily have combustion air sources necessary for the high burn rate of gas. Also, retrofitted gas devices have different clearance requirements than the wood-burning fireplace they replace. The hearth and/or mantle may need to be altered to prevent a household fire.
Whether in a new or retrofitted home there are several factors which effect health and safety: Oxygen depletion, depressurization, water vapor, gas pollutants, and heat. Professional installation of a gas log or fireplace will help prevent these hazards. Though gas fireplaces and logs are convenient it is important to follow the manufacturer’s guidelines as they have considerations specific to their design.