SB2023 Posted August 10 Share Posted August 10 Hi all Having a bit of space challenges with mvhr incoming supply and external exhaust pipes. It would make things a lot simpler if my exhaust pipe to outside could have a slight dip in it but I am worried if this will cause a mould/moisture collection point. Is that a concern? The pipe would come vertically out of the mvhr unit then run 1.5m with a slight downward fall (to avoid rafters) then .5m vertically up and out the roof. All of this is inside a warm insulated roof space that is effectively part of the house. Thanks! Link to comment Share on other sites More sharing options...
JohnMo Posted August 10 Share Posted August 10 Your trouble will be a puddle and all the unhealthy stuff this breeds. Your extract is always expelling damp air, if its wet outside the incoming air could carry moisture also. Can you install a drain at the low points? Link to comment Share on other sites More sharing options...
SB2023 Posted August 10 Author Share Posted August 10 I did think about this but worried that a drain would also let air escape, it wouldn't be truly airtight if the water needs to get out? Link to comment Share on other sites More sharing options...
Nick Laslett Posted August 10 Share Posted August 10 One of the cock-ups on my build. We have poured ICF walls, so I asked the builder to set the MVHR inlet/outlet 200mm steel spiral ducts in the wall prior to them pouring the concrete. This was near the top of the wall, the amount of concrete on top was not that great. I gave him 500mm lengths, with end caps to strengthen the ducts. I requested a 3° fall, he is Romanian, so something might have been lost in translation, he set to ducts at nearly 30°. I never checked the angle of the ducts. It wasn’t until after the concrete first floor had been poured, that I realised the angle was wrong. I wasn’t sure how big a problem this might be, but in the end I could not face rectifying this mistake. On the inside I had enough head room to fit a 30° bend to correct that angle. On the outside the external grill will be mounted on timber cladding, the plan is to fit a 15° bend to correct most of the angle but still leave it pointing slightly downwards. 1 Link to comment Share on other sites More sharing options...
JohnMo Posted August 10 Share Posted August 10 47 minutes ago, SB2023 said: I did think about this but worried that a drain would also let air escape, it wouldn't be truly airtight if the water needs to get out? How are 150mm+ ducts connected to the outside world airtight? You would drain via waterless traps, which are airtight anyway. Your installation manual should tell you to install low point drains Mine says " ducting condensate drain must be fitted to vertical To Atmosphere duct work." Link to comment Share on other sites More sharing options...
SB2023 Posted August 10 Author Share Posted August 10 40 minutes ago, JohnMo said: How are 150mm+ ducts connected to the outside world airtight? You would drain via waterless traps, which are airtight anyway. Your installation manual should tell you to install low point drains Mine says " ducting condensate drain must be fitted to vertical To Atmosphere duct work." Fair point on the airtight bit! The zehnder doesn't seem to talk about a drain on the outgoing/incoming pipework in their manual that I can see. Will look again. Link to comment Share on other sites More sharing options...
SB2023 Posted August 10 Author Share Posted August 10 A vertical condensation trap looks like it might completely resolve the risk here. That might open up my options and should probably be fitted regardless. Not sure why bpc didn't include/suggest it as they knew it was venting vertically through the roof! Link to comment Share on other sites More sharing options...
Mike Posted August 10 Share Posted August 10 3 hours ago, SB2023 said: zehnder doesn't seem to talk about a drain on the outgoing/incoming pipework in their manual that I can see. It's only the exhaust duct that you need to worry about. If that drains back towards the MVHR unit, as recommended, then any condensation will exit via the condensation pipe build into the unit. It's also acceptable to have a high point in the duct, so that part drains back to the unit, the rest to the outside. Maybe you can do that - i.e. take the vertical pipe slightly above the exhaust grille, and then angle it slightly down from there. 1 Link to comment Share on other sites More sharing options...
SB2023 Posted August 10 Author Share Posted August 10 Thanks Mike! Appreciate the thoughts. Given me some ideas and direction! Link to comment Share on other sites More sharing options...
Dave Jones Posted August 11 Share Posted August 11 On 10/08/2024 at 11:14, SB2023 said: Fair point on the airtight bit! The zehnder doesn't seem to talk about a drain on the outgoing/incoming pipework in their manual that I can see. Will look again. its the unit that has the drain in the bottom. all pipework must have fall back to the unit. 1 Link to comment Share on other sites More sharing options...
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