Can I Tie Two Bath Exhaust Fan Vents Together?

two ducts attached to vents

Most modern houses have several roof jacks to facilitate ventilation from the different rooms. In most cases, you will find a jack for the kitchen, separate from each of the bathrooms and the other rooms. Consequently, this often means having several jacks on the roof.

On the contrary, most old houses may not have these provisions. In some old houses, you will find only one jack connecting to one bathroom in the house with more than one bathroom.

Most DIYers' dilemma is handling this situation without making a hole in the roof. In today's blog, we look at a situation where a DIYer has to link two bathroom ventilation fans to one jack on the roof. The question is whether this action is legal, possible, and workable.

Legalities Regarding Ventilation Standards

If we look at the question legally, it is against many construction codes to try two bathroom fans to one roof jack. Ideally, each bathroom fan should be connected to an independent roof jack.

In other words, if you have to use mechanical ventilation for your bathrooms, ensure there's no air circulation from one room to another. The risk of using one roof jack for both bathrooms is that air could flow back from one into the other, which is illegal.

You will most likely face penalties if local construction officials find such a connection.

bathroom fan vent

Using One Roof Jack for Two Bathroom Fans

It is possible to connect two bathroom fans to one roof jack. The easiest way is using a Y connector, which links the second and first bathroom to the roof jack.

However, due to the rise of air recirculation, it is advisable to have a remote fan that helps push out moisture-loaded air from the inside. This third remote fan will go a long way in ensuring no air flows back into the house.

Venting Options

If it is not okay to connect two bathroom fans to one roof jack, what is the alternative solution: Well, one of the reasons why anyone may want to connect two bathroom fans to one shaft is lack of finances. The other would be a lack of the necessary skills when setting up a fresh roof jack.

These are legit concerns that you should consider clearly before deciding. If you have no idea how to work on the roof, you want to avoid that option entirely. You do not have to put your life at risk to get something done.

You may consider hiring experts to deal with the problem in such a case. On the other hand, if money is the problem, you may want to use a cheaper solution. The cheapest solution would be exhausting one of the bathrooms through the wall.

Although not recommended, it is safer than exhausting through a single roof jack.

vent facing outside

What's The Worst that Could Happen?

If you decide to ignore construction codes and the go-ahead to link the two bathroom fans to one roof jack, you put yourself at various risks. The first and most obvious is the risk of air flowing from one room to another. This could mess up the oxygen flow in your house and potentially harm inhabitants.

Besides air movement, there is a risk that your fan may get damaged much faster. When moisture-loaded air is passed from one bathroom to another, the fan may get corroded, and the motor may eventually stop working.

Bottom Line

The final point to keep at the back of your mind is that connecting more than one fan to one roof jack is not viable. You better use one bathroom or invest enough cash to build another roof jack for your second bathroom. This will help reduce risks such as air recirculation and moisture corrosion to your fans.