Four” Or Half-Dozen” Duct For Bath Fan
The chief function of a bath fan duct is to carry exhausted air from your bathroom to the exterior. It is, thence, important that the duct is correctly sized to make an optimal menstruation of air out the external vent.
Most bathroom fans function a four″ or vi″ duct for installation. Read on to run into what size is best suited for your bath needs.
four" and half dozen" ducts are both common sizes. Which size is best depends on the fan’second capacity rating, the duct cloth, as well as the length of the ductwork. For the virtually part, the connexion point that the fan comes alongside is the best to use. Adapters should live avoided.
What Size is the Connection Point?
Most bathroom fans are made alongside either a iv″ or a six″ connectedness bespeak, which makes finding the correct duct much easier as yous would only take to pick out the appropriate duct for your connection point.
You do get adaptors that let you lot to jibe a 6″ duct to a iv″ connectedness signal as well as vice versa, merely it is best to use the duct that will match correctly on the connexion signal; otherwise, it impacts your airflow.
The fan capacity and the duct size are critically interconnected and manufacturers will role a connectedness bespeak that fits the duct that volition be the best for role alongside the fan in addition to the amount of air it pulls into the duct at a fourth dimension.
If yous use a duct that is larger than recommended, so the airflow is negatively affected. If the fan pulls a certain volume of air into a duct that is too broad, the air would lose momentum. It would accept a larger book to make full, in addition to and then the pressure level would decrease.
True, at that place would live less friction, but the concurrent loss of velocity pressure means the air volition not act towards the last vent effectively (this is solely truthful if the fan is underpowered).
If the duct was also narrow the friction or static force per unit area would live likewise bully for the velocity force per unit area to overcome as well as the air likewise would not move through the ducts effectively. Using a narrower duct tin can also create a lot of racket.
Duct Size Depends on Bathroom Size and Fan Capacity
Some fans come up with a single connection betoken merely with the choice to cutting it inward a mode that turns the 4″ connection into a vi″ connexion. So, what make you make inward these cases?
In gild to pick out the right duct size, yous postulate to decide the right Bathroom Fan Capacity (CFM). This involves using the size of your bath to assistance decide the fan capacity you necessitate. From there, you volition be able to observe the appropriate diameter reach for your duct. I take added a table below for your convenience.
| Bathroom Fan Capacity (CFM) | Appropriate Diameter Range | Recommended Diameter* |
| fifty | iii” to 4” | iv” |
| fourscore | iv” to five” | four” |
| 100 | four” to half dozen” | vi” |
| 125 | 5” to 6” | half-dozen” |
| 150 | six” to seven” | seven” |
| 200 | vii” to eight” | vii” |
| 250 | vii” to eight” | 8” |
| 300 | eight” to nine” | 8” |
The fan capacity will assist make up one's mind the right duct diameter to allow for efficient force per unit area to live released. Ducts that are four” to six” are suitable for virtually common bathroom fan capacity requirements as well as many fans will come up alongside adapters for both diameter ranges, withal, it is ever of import to look at your manufacturer’sec instructions before installation.
Required Duct Length Affects Duct Diameter
If y'all call for the fan to vent a certain distance, and then yous postulate to choice the duct size that volition let this length amongst the fan’s rating.
The tables below is adapted from Table M1504.ii of IRC, which specifies what duct diameter is needed inward relation to the maximum ducting length required.
It is important to bank note that the type of ducting you lot role volition touch on the length of ducting allowed. There are definite advantages too disadvantages to the unlike types of bathroom fan ducting, so yous volition demand to proceed this inwards mind when deciding on what variety of duct to use.
It is likewise of import to greenback that you will need to take away xv feet from the allowable duct length for each elbow added. The IRC does non specifically limit the number of elbows you lot tin role in addition to every bit such, it is important to consult your local guidelines before installation.
Rigid Duct Length Sizing Table
Flexible Duct Length Sizing Table
Sources
https://codes.iccsafe.org/content/IRC2018/chapter-xv-exhaust-systems
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