Summary: If you thinking of venting your clothes dryer straight into the garage, not only it is an awful plan but it also might be a violation of building code. The dryer exhausts a lot of water vapor. This condensation in your garage can rust any unpainted surface that may be there. The ceiling and walls inside could develop mold, which is bad. The clothes-dryer should be vent directly to the outside.
Question: My husband plans to make sure that our cars are kept warm in winter by making our clothes dryer vent straight into the garage. But I thought dryers should vent outdoors. We have been arguing about this and are not able to settle this one way or other. Can you do something about this? Where should the vent be directed? What should we steer clear of when we install a clothes dryer vent?
Answer: The whole idea of making use of waste heat is a wonderful idea. You should applaud your husband for such a thought. But then his proposal has some hitches. It could also see him face some problems that will cost you money, trouble and time. May be it also violates building-code of your locality. Having a penetration in the wall connecting your house to the garage is also not a welcome practice.
The problem is that there is a lot of water vapor that comes pouring in from the clothes dryer into your garage. You know how much the problem is when you see the clothes-dryer pouring out a cloud of water vapor on cold days of winter. The garage receives all the liquid water in the form of vapor if your husband goes ahead with his idea. No doubt that this water vapor will then condense and get deposited on the cool surfaces there. This will cause corrosion and rust on steel parts and tools that are not protected well. The water vapor condenses in places that you are not able to see. This then leads to issues with mold and water in the garage walls as well as attic space in your garage. It is also possible that the wood might rot if the wood gets exposed to these water vapors for a along time. You might see lint all over the garage.
Often home building and home remodeling does not adequately consider dryer vents a serious enough issue to be taken care of. With only one load of clothes, thousands of cubic feet of air get expelled when dried. This is often underestimated. You are correct when you instinctively guessed that the air should be exhausted outdoors. But before the hot air is expelled, you can also catch some of that heat also.
Clothes dryer exhaust should be vent outdoors. You can exhaust them out through the roof or through the walls sideways. The hot air also effortlessly rises up. The clothes dryer come with written instructions. This should be strictly followed. The instructions go to a great length giving details of the kind of pipe to be used, and the manner in which the pipe has to be laid to the outdoors from the backside of the dryer.
The best venting materials is the smooth metal pipe. All the clothes-dryer manufacturers will advise you this. The pipe, 4 inches in diameter, should extend to a specific maximum distance, which the manufacturer will inform you. You will know what the length of the vent pipe should be from the manufacturer. You need to do some calculation where you will have to take into account the length required to turn corners for a 90-degree fittings. Generally a straight pipe of 10 feet is counted in for every 90-degree fitting.
Heat travels from the clothes-dryer through the length of the metal vent pipe. This could heat up the area along the whole length of the hot pipe through radiation. The pipe should be installed with a maximum length if you want to extract its heat. You could see whether you can install the metal vent pipe at a slope so that it runs maybe 20 feet from the dryer all the way to the window if you are lucky to have an incomplete basement.
You can also use scrap sheet metal to put together a crude heat exchanger. But then there may be lint buildup which you need to check often. So a door will be ideal to ensure that you can open and check whether there is buildup of lint. It is important to make sure that there is no lint buildup in your clothes-dryer. There is the danger that the clothe-dryer lint could catch fire.
Insulation of the clothes-dryer vent is to be done well in case the vent traverses through any cold or cool space such as an attic or a crawl space. The vapor can condense to water inside the vent due to the external cool or cold temperature if the insulation is not proper and adequate. When the pipe gets filled with water, the vent can cause leaks or the dryer will perform poorly.
The termination cap of the dryer vent should not be installed in a soffit that overhangs right under the roof. The water vapor can enter into the attic easily through any small opening or cracks and through soffit vents. The cold lumber inside the attic will then condense the water vapor. Attics with large areas coated with one-half-inch thick frost are not a rarity as I saw in photos. Sometimes there is a column of black mold located on the roof bottom immediately above the soffit, which is where the dryer vent outlet is positioned.
The dryer-vent roof caps can be easily purchased. They are connected to the smooth metal pipe which is 4-inches. There is a damper for the caps to keep the pipe free of animals. The damper should be periodically cleaned as it might get clogged by the lint.
You have to be wary if your dryer-vent kit says that the air can be exhausted inside your house. For this to work, the system will require as part of it a very large refrigerated coil to convert all the water vapor into liquid water. If there is no such coil, your home will be overrun by huge quantity of water vapor.
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