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Bathrooms without adequate ventilation develop problems.

That’s preventable.

For every bathroom, the best solution is a good bath fan. It’s the unsung hero that exhausts the moist air – and odors.
The best news is that installing bath fans is not rocket science.  It’s a project many homeowners can tackle bathroom on their own.  Even if homeowners decide to hire help, like an electrician, the project is quick, not very messy, and usually costs less than $500.

NuTone Ultra Silent ceiling fan in 80 to 110 CFM, with humidity sensor

The key is a fan strong enough to do the job.

Fans are rated by “CFM,” the cubic-feet-per-minute of air that a fan can exhaust from the bathroom.  CFM ratings are in even numbers, like 50, 70, 80, 90, 100, and 110 CFM.  There bigger CFM fans too, like 240 and 270 CFM, for larger master baths.
That means a rounded number is close enough for figuring CFM. Skip going down to the decimal point.

     To compute CFM for a bath, just multiply the width of the bathroom by its depth and then by its height.  So a bath that’s 9 feet wide, 10 feet deep, with an 8 foot ceiling has 720 cubic feet of volume (9 x 10 = 90 x 8 = 720).

Then divide the cubic feet of space by 7.5.  That’s because the goal is to exhaust bath air once every 7.5 minutes.  So that 720 cubic foot bath, divided by 7.5, will need at least a 100 CFM fan (720 ÷ 7.5 = 96).  Up it a little for small spaces.  A nice typical half bath — say, 4 feet wide, 7 feet deep, 8 foot ceilings) — is around 224 cubic feet.  Divided by 7.5, that half-bath can get away with 30 CFM, if one were made, but should use a 50 CFM most of the time, even though there’s no shower.

Check how far the fan has to blow the air to get it outdoors next.  Today’s standards require all bath fans to vent outside (not to the attic, for example).  If there is more than 20 feet of duct from the fan to the exterior, increase the CFM rating for the fan you buy.
Basic ceiling fans start around $50 and go up to $150.  Most of them include lights.  Some models have night lights too.  More and more fans are Energy Star rated.  A few have ‘green” ratings.  Most bath fans are ceiling mounted.  Wall mounts also are available.  Some units can be installed either way

Two other features also are worth considering.

For most homeowners, the best choice is a fan that also has a timer or humidity sensor built in.  Timers and humidity sensors let the fan run for another 20-30 minutes after showering to help move all the moisture out.

Whisper quiet fans make a difference for many homeowners.  Fans should be seen and not heard.  Loudness is rated in “sones.”  Quiet fans are rated 1.0 sones or less.  Most manufacturers (NuTone, Broan, Delta, Panasonic, Hunter, for example) have “ultra-silent” models rated 1.0 sone or less.

Adding those features to a bath fan is not very costly.

Good, quiet fans with humidity sensors or timers cost about $225-$350, depending on the CFM and other features.
Installing bath fans is no more difficult than changing a light fixture.  If you’re doing the wiring, only do what you know how to do safely.  Turn off power to the bath while working.  Remember black to black wire, white to white, green to bare copper get connected in a junction box.  Then cover it.

And don’t forget that a lit fans over bath tubs or showers must be connected to a GFCI protected branch circuit.
A master electrician can knock that job out in a hour or two.  That’s a better choice if you have any doubts at all.
Of course, if you’re looking at ventilation options, your trusted home inspector is a terrific resource.  InspectHomes inspectors are just a call away, every day.

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