LinearPancakes Posted August 20, 2023 Share Posted August 20, 2023 Our MVHR unit is going in our cold loft. To insulate the ducts I'm planning: 25mm armaflex wrap on supply ducts, as these could be cooled to ~14deg in summer due to ComfoPost 10mm armaflex wrap on extract ducts If I've modelled this correctly in Ubakus, it looks like there will still be a bit of condensation on the outside of the Armaflex in the worst case scenario (assuming heat wave, loft getting very hot). Applying a foil wrap outside the Armaflex looks like it will prevent this. Though I imagine it would be tricky to apply this well enough to provide a sufficient vapour barrier in practise. I also bought some foil faced fibreglass duct wrap that I'd planned to use outside the Armaflex to reduce heat transfer where not covered by loft insulation. But condensation skyrockets when I apply a similar setup (mineral wool). Better with foil wrap, but again, I doubt in my ability to make it a good enough vapour barrier. I find this curious, as if there's no condensation build up on the Armaflex. So my questions are: Would you expect the foil wrap outside the armaflex to help condensation that much? Will I get huge condensation issues applying the fibreglass ductwrap around the [possibly foil lined] Armaflex? I guess I could just double up to 50mm armaflex, but it's pretty expensive stuff. I was hoping 25mm Armaflex and then fibreglass ductwrap would be fine. Thanks for any insight you can give. Screenshots of Ubakus attached. Link to comment Share on other sites More sharing options...
JohnMo Posted August 20, 2023 Share Posted August 20, 2023 Are you sure the ambient and humidity levels are correct? Link to comment Share on other sites More sharing options...
LinearPancakes Posted August 21, 2023 Author Share Posted August 21, 2023 Not for certain, but I was trying to pick a worst case. Maybe 50 degrees would be a more realistic peak in a heatwave, but I don't think it would change the calculations significantly. Link to comment Share on other sites More sharing options...
JohnMo Posted August 21, 2023 Share Posted August 21, 2023 If the roof space is at 50 -55deg, it unlikely to have a humidity level of 60% at that temperature? Also if you are cooling the air the humidity level is likely to increase, the air in the pipe is likely to be at or close to 100% humidity. Link to comment Share on other sites More sharing options...
LinearPancakes Posted August 22, 2023 Author Share Posted August 22, 2023 You're right, thanks. I believe the last heatwave was 41deg peak and ~25% RH. So in a loft heated beyond that, the RH would be even lower. Looks like the plan for 10mm armaflex + 50mm ductwrap for extract and 25mm armaflex + 50mm ductwrap for supply will not have any significant condensation, even in worst case. Link to comment Share on other sites More sharing options...
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