Possible Safety Danger
Garage venting presents a serious threat and should not be considered a viable option according to experts. Before installing a dryer, and especially a gas dryer, contact a certified technician to ensure that the dryer is properly vented to the outside. Indoor dryers, that are not properly vented can result in dryer vent fires, injuries and deaths.
Increased Health Hazard
Gas dryers that are vented into your garage can be especially hazardous. The marginal benefit you may realize in heating the garage is offset by the highly probable build up of carbon monoxide and possible poisoning of you and your family, according to the Iowa State University Extension website. In addition, the increased moisture vented into your garage can result in mold and mildew, harming the garage's wood structure, tools, and other stored items.
The best option is to vent your dryer directly outdoors. If this is not possible, and you have an electric dryer, try a dryer lint kit, which captures dryer lint as well as the considerable amount of water vapor that is emitted from the dryer vent. Once the container is filled with water, it traps the lint. Or use a solar clothes dryer, otherwise known as a clothesline. The sun's heat will dry your clothes and it is safe, and cost effective.