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Ducting sloped or level


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As I understand it, it is good practice to have a slight slope on ducting as it passes through a final wall to an exterior vent in case of rain getting in. If the ducting passes through an unheated area then it makes a lot of sense to have a slope and possibly a condensation trap if case of water condensing in the ducting. It may all be more relevant to a bathroom than a kitchen, but is it normal to set the ducting level or sloped in a particular direction?


I haven't found any results in Part F (Ventilation) for slope, gradient or fall and there is one mention of the word drain, but associated with MVHR:



The main reason I ask is because I am connecting from rectangular to circular ducting in what I think is an unconventional way. In order to fit behind a soil pipe, I am mounting the rectangular ducting with its long axis vertical. This means that when it connects to the circular ducting, there is an uphill slope in the direction the air is extracting. If water was to condense in the ducting it would pool at the adaptor. There is so much air flow that I'd imagine any condensation would re-evaporate pretty soon, but I wanted to check if I should be doing something about this.


EasiPipe 125 In-Line Adapter Round 125 to Rectangular 204x60 - Domus  Ventilation



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The reason MVHR has condensate is because the exhaust air is cooled as it passes through the unit.  If this is just a normal extract and the ducting is inside there will not be an issue.  It can run up, down, left and right.  It is only when it approaches the outside that it will possibly cool enough for condensation to be an issue.

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