Does a Bathroom Fan Need to Vent Outside

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Many homeowners are unaware that their bathroom fan is vented incorrectly. If moving to a new house, it is very important to check or hire a home inspector who can tell you where the bathroom fan vents to. Unfortunately, some contractors attempt to take shortcuts and send the exhaust directly into the attic.

A bathroom fan must always be vented to the outside. This is required by building codes almost everywhere in the world. Even if the local building code does not require it to be vented outside it is always best to do so. Venting the fan out of the building envelope will prevent moisture damage and expensive mold removal.

Exhaust fans are not designed to be vented into the attic. Moisture will condense on cold surfaces in an enclosed space and the bathroom will produce enough moisture that it could cause mold growth or damage wood, insulation materials, etc…

Venting outside also prevents odors from being recirculated throughout the house which helps with indoor air quality (IAQ) issues as well!

Why Should The Bathroom Fan Vent Outside

Let’s start with why it is important for the bathroom fan to vent outside. When the moisture is ventilated to an indoor space, moisture builds up on surfaces and creates ideal conditions for mold and mildew growth.

This can lead to respiratory issues as well as a foul smell from bacteria growth inside these moist environments. Mold spores and bacteria are hazardous because they can cause allergies or asthma symptoms such as sneezing.

Mold is just one out of 9 reasons why having no ventilation in the bathroom is terrible.

What’s more, the excess moisture could even eventually damage the homes construction.

Venting to the Crawl Space is Not Considered “Outside”

One might think that it’s OK to terminate exhaust fans in the crawl space. But it’s not!

The moisture will cause a myriad of problems under the house and can be even worse than having no ventilation at all.

During wintertime, the cold humid air that is exhausted into the crawl space will condensate and cause metal fasteners to rust and wood to rot. Before long the crawl space will be crawling with mold spores. Mold removal from the crawl space is extremely time-intensive(read expensive)

Venting Outside Will Keep Your Home Free from Mold and Mildew

The contractor may have been trying to save some money by venting the bath fan into your attic, but his/her mistake could end up costing you thousands in mold removal.

Fortunately, it won’t cost a fortune to vent the bath fan correctly – this job can be completed on Saturday and for $50 or less!

Here is a list of everything you will need.

ItemView on amazon
4-inch Stainless steel hood*View
4-inch Spring Loaded DamperView
4-inch duct & 2 clampsView

Learn more about what kind of duct to use for venting a bathroom fan

Venting The Bathroom Fan Into The Attic Will Saturate The Insulation

The excess moisture that is vented to the attic will saturate the insulation. The R-value of insulation will be significantly lower if it is saturated. This will in turn increase your home’s energy bill.

In extreme cases, if the attic ventilation is very poor and the bathroom has been vented to the attic for years, some of the insulation could even have to be replaced. Replacing insulation and removing mold is very expensive.

That’s why it’s very important that the exhaust fans in your home, including bathroom fans and range hoods, be vented outdoors.

Fog Machines Are a Great Way to Test if Your Bathroom Fan Vents Outside

A fog machine(amazon link) is an effective, low-cost solution for testing whether or not the exhaust fan in your bathroom is vented properly. It can also be used as a quick and easy method of checking for leaks in the venting system.

Simply place it next to the exhaust fan and have someone else look out into the yard while you turn on the machine.

If no smoke is coming out of the outdoor vents, then the fan is probably vented to the attic.

Note: The smoke from the fog machine is not dangerous, it is usually used for parties.

Can Ductless Fans Be Used In a Bathroom

A ductless fan should never be used in a bathroom with a shower or a bath. They are designed for quarter baths, pantries, or closets.

No matter the model, it is impossible for a ductless fan to remove moisture.

Other Ways of Ventilating The Bathroom

Undoubtedly a vented bathroom fan is the best choice for ventilating a bathroom. There are other options that are much better than a fan that vents into an indoor space.

If your bathroom fan does not vent to the outside it is best to not use it until a duct is installed and the moist air is exhausted out of the house.

Open a Window

If your climate allows, open a window whenever showering, and leave it open until the bathroom has dried out.

Leave The Bathroom Door Open

Leave the bathroom door open during if possible, and after showering. This will allow for the moisture to dissipate in the entire house and the whole house ventilation system will exhaust it out of the house.

This way the moisture won’t be trapped in a small room.

Use a Dehumidifier

While I always recommend installing a proper exhaust fan since it is more effective and has lower running costs, a dehumidifier will remove the moisture from the air as well.

Make sure you don’t buy one of the tiny models. One shower creates enough moisture to fill it’s tank.

Instead, look for a model with continuous drainage(amazon link). This way you never have to empty the water tank since the water collected by the dehumidifier is flowing directly down the drain.

Install a Wall Mounted Exhaust Fan

If installing a duct for your current bathroom fan is impossible for some reason. You could simply install a new wall-mounted exhaust fan. It is relatively easy to install a wall-mounted fan since no ductwork is required. If your bathroom is on the second floor, you will need a long ladder to mount the fan grill from the outside.

Is There a Bathroom Fan That Doesn’t Vent Outside?

Wouldn’t it be great if there was such a thing as a bathroom fan that does not require any ducts.

Unfortunately, it is not possible.

In order for a bathroom fan to be effective it MUST vent outside.

There are ductless bathroom fans for sale in every home improvement store. While their name implies that they are meant for bathrooms, they really are not. Since all they do is circulate air through a carbon filter no moisture will be removed from the bathroom.

The only way to effectively ventilate a bathroom with a shower and/or a bath is to install a bathroom fan that is vented to the outside.

All other options will end in moisture damage sooner, rather than later.

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