The problems with ventless gas fireplaces that have been reported by consumers include health-related issues such as headaches and respiratory problems, excessive moisture, soot and a bad odor. Additionally, ventless gas fireplaces may cause discoloration to walls and structural damage to drywall, flooring and furniture due to water absorption.
Ventless gas fireplaces produce gas byproducts that include carbon monoxide, carbon dioxide, nitrogen dioxide, formaldehyde and water vapor. Without proper ventilation, these gases cause many health problems. Carbon monoxide, a colorless and odorless gas, is known to cause symptoms ranging from mild headaches to death. Carbon monoxide is especially dangerous to pregnant women, the elderly and children, and people with asthma.
Carbon dioxide, while harmless in small amounts, can cause eye irritation and an elevated respiratory rate. Excessive amounts of nitrogen dioxide can lead to a dry nose or throat. Excessive amounts of water vapor can encourage the growth of mold and mildew, which is especially harmful for those with respiratory problems. Formaldehyde gas is linked to various health problems such as eye, nose, throat and skin irritation; nausea; and coughing. Additionally, studies done by the National Cancer Institute have linked an increased risk of leukemia and brain cancer with prolonged exposure to formaldehyde.