Under the International Residential Code (IRC), it is illegal to combine dryer ducts with any other exhaust system inside a house. The answer is no, you cannot vent a dryer and a bathroom fan together. There are several reasons why this is the case. The only viable solution in this situation is to lay separate ducts to the outside, as should have been done initially.
As you can see, it's a violation of the codes for good reason. Both conduits must be rigid or semi-rigid tubes, as appropriate. By venting the dryer and bathroom fan separately, you can also prevent condensation from accumulating in the bathroom. If you were to vent the dryer and bathroom fan together, the lint could enter the bathroom and cause a fire.
Therefore, if you want to improve ventilation in your home, it's best to ventilate the dryer and bathroom fan separately. If you were to vent the dryer and bathroom fan together and a fire breaks out, you could be held responsible for the damage. Additionally, if you vent the dryer and bathroom fan together, the lint could clog the drains and toilets in the bathroom and cause them to accumulate. If you were to ventilate the dryer and bathroom fan together, you could create an ideal environment for mold and mildew to grow.
If the dryer duct is combined with a fan duct, dirt and debris that the fan has carried can accumulate inside the dryer duct, increasing the chance of clogging and heat accumulating. You might think that venting your dryer and bathroom fan at the same time will save you time and energy, but this is not true. Keeping the dryer ducts clean is also critical to preventing damage to the dryer and keeping the system running safely. One of the biggest issues with a bathroom fan and a dryer that share a vent hole is the buildup of lint.
Therefore, if they are combined, it makes cleaning more vital but at the same time makes cleaning difficult. The size of the exhaust ventilation used by the fans must be increased by one inch for each fan that shares the same ventilation. Cleaning these ducts is essential because dryer ducts accumulate lint, which can generate mold, which is a health problem, and if this lint dries, it becomes a fire hazard. If you were to vent the dryer and bathroom fan together, you could be held responsible for any damage caused by a fire or clogged drains or toilets.
Let's take a closer look at why bathroom fans and dryers cannot share a ventilation grill and what some of the consequences would be if they did. If you live in an area where local building inspectors don't allow dryers and bathroom fans to enter together, they could fine you or even convict your home.