Vents ar often fitted with a draught preventer which looks like little plastic venetion blinds. I put my hand up to the vent and didn’t feel any cold air. The hood in the kitchen. Between the two of them it does a good job of stopping massive drafts but the long run of duct and the thin metal damper doors are not insulated so even without wind you can feel some cold air falling down the duct and out of the vent. When its off with the slightest wind outside cold air comes in. One is at the top of the hood, where it connects to the duct, and the other is at the wall or roof cap where the duct exhausts its air. One is located just above the fan blower where it connects to the duct and the other is on the roof. Allow her to give you a full report: "It's been frigid here in NC yesterday, and expected to get down to 0 degrees over the next few days. We're getting a lot of cold air blowing back down through the extractor and out into the kitchen. This is a substantial energy-loser that causes cold drafts to enter your bathroom and house! Why Do We Need Exhaust Fans? These thin metal flaps don’t form airtight seals because they have to open when the hood’s fan is working at low speed, but they should keep the cold drafts, and the hot ones, from coming in through your hood. But during the cold-weather season, exhaust fans may also make it too easy for frigid air to creep in. Hi Steve, Fans normally come with a finial with fins that drop down and close the vent when the fan is turned off, depending on the type of fan it is either part of the housing, or for inline fans a separate article, it sounds as though somebody omitted fitting these, they are … When working properly, the flap should close when the vent fan is not in use, and open to let air escape when the fan is in use. I need to know if there is anything that can be bought to block (placed over) the vent when swiched off. Is there any way to stop it, such as a valve of some kind or a different type of exterior vent? In bathrooms and kitchens, overhead exhaust fans are used to pull unwanted airborne particles out of the room and into the atmosphere. This will be because (1) wind direction and (2) there is not an effective control to stop air blowing in. Bearing in mind it is a ceiling fan. Is anyone aware of a fix for this? Bathroom extractor works fine, when switched on, getting the air out. In the winter, cold air leaks in through the duct and into your bathroom, while your heated air just pours right out! Cold Air Kitchen Exhaust Fan Q & A | Ventilation text: Tim Carter. There is very cold air coming in through the hood. Maggie Scofield is suffering from cold air that's coming down through her kitchen exhaust fan in Raleigh, NC. I guess they are supposed to have flaps in them too. 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