# What size exhaust fan for my bathroom

Choosing the Right CFM Size for a Bathroom Exhaust Fan

Jul 21,  · For a standard 10ft by 10 ft bathroom with an 8 ft ceiling, you will need an exhaust fan capable of CFM. Here’s how we get this number: (10ft * 10ft* 8ft)/ = CFM Bathroom Fan Exhaust Size Calculator. Sep 11,  · If your bathroom has an 8’ ceiling, the CFM rating for your fan should be as least as high as the number of square feet (5’ x 7’ = 35 sq. ft.) in the room. So in your case, a 50 CFM fan should work. A bathroom with a higher ceiling would require a larger fan.

By Glenda Taylor and Bob Vila. Q: We recently bought a beautiful old house, but the former owners never installed a vent fan in the bathroom. After a shower, the mmy is completely fogged and the walls are wet to the touch. How can we figure out the size and type of bathroom fan we need? A: Good thinking! A bathroom ventilation fan will definitely reduce the humidity caused what is the best hybrid bike to buy bathing and showering, and it will protect your bathroom from moisture damage in the long run.

Early models took an inefficient, one-size-fits-all approach, creating more circulation and noise than was necessary in small bathrooms and not enough circulation in large bathrooms. Fortunately, manufacturers have spent the past 15 years focusing on producing highly efficient fans designed to suit bathrooms of specific sizes.

A fan with the correct CFM should draw in enough air to refresh all the air in your bathroom at least how to clean a rock river ar15 times per hour.

To get the total square footage, multiply the length of your bathroom by its width. That basic formula for an average-size bathroom needs a little tweaking if the ceiling stretches past the qhat 8-foot height. If bahroom aforementioned square-foot bathroom has a foot ceiling, we would use the following formula to determine the correct CFM:. This separate feature enables you to bathroo, the fan speed to suit your needs, so you can turn it down when shaving in the morning and turn it all the way up for a steamy shower.

For bathrooms larger than square feet, you can base your target CFM on skze number of fixtures in the bathroom. Just add up the numbers below that correlate with each fixture in your bathroom to determine the appropriate fan size for the space:. A large bathroom with a jetted tub, a toilet, and a shower—a common configuration in new homes—would need a CFM ventilation fan, such as the Broan L Ventilation Fan available from SupplyHouse.

These small enclosed stalls are popular for ensuring privacy in large bathrooms that boast open access to walk-in closets.

A 50 CFM fan is usually sufficient. Note that when choosing a fan to install directly over a shower, dize fan should be whatt for installation in wet areas and should be connected to a GFCI outlet or breaker. Bathroom fans are rated from 0. A sone exhust of 1, on the other hand, is similar to the gentle hum of a refrigerator. A rating of less than 1 will be so quiet you may not even notice that the fan is wize The Fantech not only offers a very quiet 0.

After figuring out how much power you gor in a vent fan, ask yourself if you could benefit from some additional options. Connect your phone and play whatever you want from your fan. This article has been brought to you skze SupplyHouse. Its facts and opinions are those of BobVila. Disclosure: BobVila. You agree that BobVila. All rights reserved.

Expert advice from Bob Vila, the most trusted name in home improvement, home remodeling, home repair, and DIY. Bafhroom Solved! Get started with this handy cheat sheet of formulas that will help you select the right size fan for your bathroom, and then learn about a few cool features that are worth a look.

Find trusted local pros for any home project. Find Pros Now. What size exhaust fan for my bathroom From Bob Vila. Stop Moisture Damage with the Flip of a Switch. The Best Bathroom Lighting. Newsletter signup: You agree that BobVila.

Maximum & Minimum Bath Exhaust Fan Duct Length

Feb 17,  · A square foot or smaller bathroom needs a 50 CFM fan. For bathrooms between 50 and square feet, estimate approximately 1 CFM per square foot. If your bathroom is larger than square feet, tally the CFM requirements for the individual fixtures to estimate your needs. Bathroom vent fan size & noise level choices & specifications. How to install a bathroom vent fan. Bath exhaust vent fan sizing & noise rating choices: here we explain how to determine the necessary capacity in CFM for a bathroom exhaust fan; how to choose a bath vent fan based on its noise level rating in sones. This article series explains why bathroom vent fans are needed and describes good. Small Bathrooms: HVI recommends that in small bathrooms, up to square feet of floor space, the exhaust fan be sized to provide a ventilation rate of 1 cfm per square foot (about eight air changers per hour). This usually results in a ventilation requirement of less than 50 cfm, so the code minimum fan size must be used. Example 1.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website. A bath vent fan duct that is too short may violate the manufacturer's installation instructions, may not work properly, or may be drafty; a bath vent fan duct that is too long may restrict air flow such that the fan is not functional.

This bath vent fan installation, troubleshooting, repair article series explains why bathroom vent fans are needed and describes good bath vent fan choices, necessary fan capacity, and good bath vent fan and vent-duct installation details. You note for the best bath vent fan duct termination to route the duct: horizontally through the building wall at a building gable-end wall first choice , or if the gable end is too distant Our bath vent fan duct installation photo shows use of solid metal 4" ductwork conducting the fan exhaust to an outdoor soffit under a cathedral ceiling roof.

Any condensate in the ductwork drips to outside - a possible winter icing worry, but because of the solid foam insulation there should be little condensation in the fan duct. Also we insulated the full outdoor soffit bay where the duct exits the building to avoid condensate icing.

Take a look at the vent fan installation manual for the particular bathroom vent you are installing. Because bath and kitchen vent fans vary in their power, the length of the vent ducting could provide enough airflow resistance to a small vent fan that it would not work properly. In our photographs above, courtesy of Galow Homes , three long, un insulated bathroom exhaust fan ducts cross the cold attic floor of a New York home and then join together at a common sidewall exit of the same diameter.

There is little chance that these bath vents will work effectively and a good chance of pooling condensate in the low spots of the duct run. Watch out : be sure to see the details of duct length limits given just below on this page.

For higher CFM exhaust fans and for longer runs, you will need to use a larger-diameter exhaust duct than the 4-inch minimum. The bath vent fan installation manuals we reviewed did not specify a maximum exhaust duct length, they just say route the duct to the outdoors.

We haven't yet found a bath vent fan manufacturer's spec nor building code or ASHRAE specification limiting the horizontal run length for bathroom vent fan ducting, perhaps because the normal size of residential buildings means that the duct run length will be within the operating capacity of currently-sold bath vent fans.

But we do have some specific suggestions for a good bath fan vent duct installation and some duct length specifics as well:. Watch out : there is no one right answer to "how long can I make my bath exhaust vent duct run? So we need to know the Brand and model of the exhaust fan and then to look at that manufacturer's specific installation instructions that will include duct length and length-equivalent numbers for each elbow or bend.

The length of exhaust and supply ducts used with ventilating equipment shall not exceed the lengths determined in accordance with Table M Exception: Duct length shall not be limited where the duct system complies with the manufacturer's design criteria or where the flow rate of the installed ventilating equipment is verified by the installer or approved third party using a flow hood, flow grid or other airflow measuring device.

Fan airflow rating is in cubic feet per minute or CFM at 0. For noncircular ducts, calculate the diameter as four times the cross-sectional area divided by the perimeter.

This table assumes that elbows are not used. Fifteen feet of allowable duct length shall be deducted for each elbow installed in the duct run.

Any length of duct of this size with assumed turns and fittings will exceed the rated pressure drop. But there is an exception to this advice: for remote vent fans such as the Fantech bath vent fan.

Fantech recommends a minimum of eight feet of insulated flex duct between the exhaust inlet register or grille and the fan motor. The company does not cite a maximum exhaust duct length.

To avoid unnecessary reductions in air movement through the bath vent exhaust system, avoid elbows and bends as much as possible. Industry experts recommend 60 cfm to 80 cfm for small bathrooms and to cfm for a large bathroom with a steam generator. The reason that there is no one right answer to "how long can I make my bath exhaust vent duct run?

The exhaust vent must comply with local codes that in turn are typically adopted versions of the IRC Section M So we need to know the Brand and model of your exhaust fan and then to look at that manufacturer's specific installation instructions that will include duct length and length-equivalent numbers for each elbow or bend.

Also, though I emphasize that following the instructions for your specific exhaust fan are the first place to check, the fan manufacturers also include exhaust vent fan length calculators. For example Broan's calculator is at www. There you'll see that for higher CFM flow rates some fan models won't be acceptable period while others according to Broan and I doubt this are shown as "NL" or "no limit on length". Watch out : using these fan calculators you can quickly get in trouble: that means having a fan that won't actually work or that will give a fire hazard - if you do not watch every parameter you enter with great care.

Some of the fan models will show "no limit" to duct length that I question but look again: the calculator may have changed the vent duct diameter from 3" up to 7" or 8". Is there a minimum distance from your outside main gas line and meter that a bathroom fan can be vented out to at the side of your house?

I haven't seen a gas code specification for the required clearance between a bathroom exhaust vent fan outlet and an incoming gas line or pipe at the building, perhaps because an exhaust vent opening should be venting only one-way: from the building interior to the outdoors. Second, gas piping should not be leaking, and if it is, you should smell the gas leak and repair it immediately. If you are concerned that the exhaust fan flapper that should close to prevent back-drafts of outdoor air into the building could malfunction and admit leaking gas from an LP or natural gas pipe or from the gas vent found at an outdoor natural gas meter, if you match the TEN FOOT clearance distance required between an air conditioner air intake and an LP gas tank, since that is the largest clearance that applies for most residential building conditions you should be ok.

You note the best practice is to terminate the bath vent duct: horizontally through the building wall at a building gable-end wall first choice , or if the gable end is too distant.

Good question. Naturally we want to keep the fan duct run as short as possible. I reviewed various industry sources and did not see a maximum allowable distance, but typically we see it's 10 - 12 feet or less.

Longer duct runs provide more air resistance, a problem you can mitigate by using solid metal ducting or metal flex duct rather than the more sinuous plastic and wire flexduct often found in these installations. The bath vent exhaust duct shown in our photo above left continued to snake across the building attic - too long, too many turns, too much up and down variation in slope - it was an ineffective installation that collected condensate inside the ductwork.

On - by mod - 4-inch diameter fan duct can be acceptable. From the fan specs " Fan shall have corrosion resistant galvanized steel housing with four-point mounting capability. Bottom line : a 4-inch exhaust duct diameter is perfectly permissible and will work fine as long as the CFM rate of the fan OR the length of duct run including effects of elbows or bends does not exceed what the manufacturer recommends.

In those cases a larger duct may be the solution. Thanks for the discussion as well! Chad Certainly a manufacturer's instructions are most-important to follow. I'd like to have a copy of that manual for review, and to see the manufacturer and the age of the product and its information. Thank you for the helpful discussion.

Thanks for the reply. That is what is confusing to me. When I started to research maximum runs for ducting, I stumbled on to this site which has charts that indicate a fan with CFM can not use 4" ducting yet the installation manual for this CFM fan never mentions any other ducting other than 4".

These are the only two places where ducting is shown or mentioned. The first is in this picture. The second is literally step 7 of the installation procedure that says "Connect 4 inch Round Duct". That's it. On - by mod - do I have to go up to a 6-inch diameter exhaust tube?

Chad There's no trouble finding an adapter between duct sizes, but we ought to start with a very careful review of the fan manufacturer's installation instructions. Comply with those specs on duct length, elbows, diameter, etc and you'll be ok, including use of a 4-inch duct, as you can also see in the tables above on this page.

Other sources vary slightly from these numbers. I am finally finishing a basement bathroom that was originally roughed in when the house was built 11 years ago.

The size of the room calls for a fan rated at 85CFM. The bathroom is at the front of the house, basically under the front porch, leaving me little options for venting at the nearest exterior wall due to the porch and a wife who does not particularly care for a vent on the front of the house. I believe I am going to have to run the vent to the side of the house which is approximately feet from vent placement. The fan comes with a connection for 4" vent tube.

Am I going to have to use an adapter to go up to 6" tube? So connect 4" pipe to van, go up to 6" pipe, then go back to 4" at the connection to the exterior louvered cap? PJ Ask your local code inspector if she will accept your deviation from the loc as k code if you are following the manufacturer's instructions.

Generally a 4 inch flex duct can carry a fan exhaust for up to 25 ft. Most codes require that. On by P. How do the codes apply to Fantech fans, particularly where Fantech recommends their 4" flexible insulated pipe attached to a CFM fan the specs show that its max is actually CFM. I want to connect the vent in the bathroom to about 1 foot of rigid, then one 90 degree rigid elbow, then connect that to about 17' of Fantech's flexible duct running vertically before venting to the roof.

I don't want to install the Fantech fan if the inspector is going to tell me it is not permitted. FWIW, my bathroom has a window, so maybe I can just install it, even if it's not to code? Lastly, I've contacted Fantech, and they are totally unhelpful. I should add that I only need about 60 CFM if I do the length, width, height calculation method, and the Fantech website says I need 64 CFM but does not provide any explanation for how that is calculated. On - by mod - factor in elbows and other restrictions in maximum duct length and minimum duct diameter as well as fan cfm.

Anonymous and Curt: just check the total equivalent duct length after you've factored in elbows and other restrictions, to be sure the CFM will be adequate. Is This Acceptable?

The Powder Room is in the center of the first floor, without access to the exterior walls. However, we can run a 4" foam-core PVC pipe up through an insulated interior wall on the second floor, to the attic. Once in the attic, we would run a 5' heavily insulated duct to an existing un-used roof vent installed by roofers. The powder room is 25 sq. We plan on installing an exhaust fan with CFM to quickly exhaust the air and to have a more powerful unit.

Any advice, comments, suggestions, or warnings would be greatly appreciated. On - by mod - proper location of exhaust vent fan outlets - code. Anon 4 baths but 3 fans - so I'll just deal with the 3 fans.

Your inline exhaust fan has to thus be have a CFM capacity before allowing for losses due to duct size, bends, material, restrictions in air flow and duct length. For that air volume 8" diameter vent ducts are close to their limit and 10" is indeed preferable. The inline exhaust fan can go anywhere in that length when you figure that the forces it has to overcome include BOTH the losses on the fan's suction or inlet side AND the losses on the fan's outlet side.

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TheBlamedSaints Change the save to option. Your saving it on your drive, change it to desktop or some other location. Hope this helps