yuumei

Follow up: I asked our councils building control and they said: So as assumed you are able to, it's just the document is not correct (IMO)

Thanks both, I found a sentence: "Background ventilators 1.72 To avoid unintended air pathways, background ventilators should not be installed with mechanical ventilation with heat recovery." So I guess this overrides the previous statement when replacing windows. Reason I'm asking is I got a CO2 monitor recently and found it goes up to about 3000 ppm overnight, we did try leaving the trickle vents open but it got very cold recently.

Sorry for what seems like a common question but I can't see the answer. I would like to install MVHR to reduce the CO2 levels in the house and eventually replace the windows to remove the trickle vent holes. However upon reading the building regulations (part F) It says: "Replacing windows Existing windows with background ventilators 3.14 If the existing windows have background ventilators, the replacement windows should include background ventilators. The new background ventilators should comply with both of the following conditions. a. Not be smaller than the background ventilators in the original window. b. Be controllable either automatically or by the occupant. If the size of the background ventilators in the existing window is not known, the ventilator sizes in paragraph 3.15 may be applied." Which I read as, when replacing windows if the existing ones have trickle vents, the replacements must have them too. Regardless of having MHVR or not. Are only new builds allowed to get rid of trickle vents?

Yes, wondered about that, we would like to use it as storage. But didn't think about a loft hatch that might work. Thanks for the idea

Hi all, I'm looking to insulate our garage to make it a bit nicer to work in. However our rafters are only 70mm deep. Is that unusual? Seems shallow compared to what most people seem to have. From what I have read we need a 50mm air gap since it will be a cold roof. Is my best bet to extend the rafters to make them deeper, then install deeper insulation? Or the alternative is 25mm of the expensive phenolic insulation stuff, then add some more on top. The other issue is the diagonal supports (? in the image). How have others dealt with insulating over these? Any comments much appreciated. Thanks

Thanks for the comments John! Yes I think the issue is that when both AC and MVHR are set could be balanced but then when anything is turned up or down it will unbalance it. I think MVHR isn't too much of a problem since it will be on low 99% of the time and boost only for a small time. I am still worried that when the MVHR Is on low and the AC is turned up, it might get past the non return valves and exit that way which would be a bit pants.

There have been one or two threads on how to combine MVHR and AC but I don't think there is consensus on it I want to retrofit AC and was thinking to do MVHR at the same time. I think having the indoor unit in the loft with ductwork going to the rooms is the easiest. What do you think of this layout for reusing the AC ducts for MVHR too? (If I didn't have the "zoning" part, I could probably do away with the one-way valves)