The first thing to consider is that the size of the bathroom determines how large a fan you’ll need. The most common duct diameters for bathroom exhaust fans are 4″ and 6,” and there’s a reason for that. However, you must think about how much ducting space you have since there is no use in using a wide duct if you can’t fit it in the walls. Furthermore, utilizing a duct that is too small generates a significant amount of noise. The narrower the duct, the greater is its resistance to airflow and airflow rate. This is because a larger number of air currents flowing through the duct will not contact the duct’s walls. The greater the duct’s width, the more efficient the ventilation system is in terms of duct diameter. How Does Duct Diameter Influence the Airflow? This is why bathroom fans are rated in CFM. A series of increasingly lower pressures thus replace the high-pressure area, and pollutants are carried with it as they move through each progressively lower pressure zone toward the outside.įor fixed duct dimensions, the more powerful the fan, the greater the pressure produced and the faster the air travels along with it. Furthermore, as the distance from the fan grows, the duct pressure decreases.Īmbient air is sucked into the fan from the highest-pressure region, which causes relatively low pressure behind it. The fan’s rotation creates a high-pressure zone behind it, drawing air into the duct.īecause the air outside is not restricted to a specific volume, its pressure is lower than the air in the duct. The negative pressure gradient causes air to move from the bathroom to the outdoors. When you install a bathroom exhaust fan and duct system, the space is actively exhausted.īecause of this, when you close the door to your bathroom, all of the air in the house is pushed toward one area. How Ducts Conduct Bathroom Air to Outside The length and width of the ducts can change the pressure system. ![]() The duct needs to be the right size so that there is enough pressure to get air from one room to the next. Increasing fan strength lowers the permitted duct length at a constant diameter.Ī bathroom fan duct is used to take the air out of the bathroom. Increasing duct diameter allows for longer ducting at a constant fan strength. Fans for larger rooms require stronger motors and bigger ducts. Most bathroom fans are available in four-inch (4″) and six-inch (6″) diameters. Install a 6″ duct regardless of the fan’s size if the length is more than 25 ft. ![]() It’s OK to have a duct that is as long or longer than the fan opening.Īlways use a 6″ duct if the fan housing has a 6″ connection, even if the fan comes with a 4″ adapter. The size of a duct is determined by the bathroom fan capacity. ![]() Supply ducts take fresh air into the house from outside return ducts go outside after warming up inside.īranch vents transfer warm moist air from rooms with radiators or clothes dryers to other house parts, and exhaust ducts carry stale indoor air outdoors through a roof vent. There are four main types of ductwork such as supply, return, branch and exhaust. The ducts are responsible for moving air from one area to another and can be an important factor in making sure your home’s ventilation system works efficiently.ĭuctwork isn’t just limited to carrying air it also carries water vapor or steam from radiators and clothes dryers. Please drop us a line if you have any specialist requirements.Ductwork is a crucial part of your ventilation system. If you have access to roof space, an inline extractor fan system would be quieter and more efficient. The silent fans are particularly popular. Units with integral or inline back draft dampers stop drafts coming back down the ducting and prevent condensation build up within the system.īathroom extractor fans generally need to extract between 10 and 20 times the volume of the area of the room it is applied every hour, depending on use, i.e a 12m3 bathroom / shower area would require an airflow of 120m3/hr to 240m3/hr. Use a centrifugal bathroom fan if your duct run is longer than a 1.5 mtr and up to 12 mtr, although they are physically larger this type of fan motor offer greater pressure. Bathroom Extractor Fans, quiet fans for wall, ceiling and window mounting, high airflow low dB shower fan options, intermittent or constant extraction available on 230V or SELV Low voltage.īathroom fans of axial type are suitable for mounting through the wall and in the ceiling if using a very short duct run.
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