“California and other cities on the East Coast and Texas have passed laws restricting or banning vent-free models, requiring gas fireplaces to have outdoor vents — though older homes in those cities and states may still have them.”

https://www.fox17online.com/money/consumer/dont-waste-your-money/woman-says-her-ventless-gas-fireplace-put-her-at-risk-for-carbon-monoxide-poisoning?fbclid=IwAR1nq4JPktvDl2c5-dG884bCi-3yf_Y24NaalCuYn6BY5XsElnw-DZGS9e4