PeterStarck

Yes there would be a degree of passive stack effect but how much would depend on the total area of the trickle vents. It would cause some probably noticeable draughts. We use passive stack ventilation in the summer to cool the house by opening the bathroom roof window. It can be very effective. Sorry re-read your post and the answer is no.

We've got a Dymo LetraTag and have ended up using it far more than we thought we would.

Worked for us. IIRC we sandwiched the existing panel with 6mm ply although I can't remember the grade exactly.

We had catflap in our old bungalow back door which we didn't want. I took the catflap out and fitted a piece if thin plywood on both sides, painted it and it was still fine when we demolished the bungalow fourteen years later.

It will be interesting to see how interested your BCO is in the ventilation calculations. Our BCO wasn't interested at all. We use the EASHP to heat our 180l DHW tank and as we never use that much hot water at a time the tank recovers quite quickly.

Yes I agree, that's why I said there was confusion because you were talking about @Thedreamer's build and I was talking more generally about the GS200 as was first discussed by the op. We got there in the end.

Correct. If an older house has an existing ventilation system ie trickle vents and I add one of these units then I haven't found anything in Part F that indicates I have to update the ventilation levels. I therefore don't need to extract 50l/s from inside the house but can extract a proportion of that from inside the house and the remainder from outside the house. I will just be enhancing the existing ventilation system.

No it wouldn't because I would only be drawing, in my example, 17.5l/s the remaining 32.5l/s would be coming from the external vent.

I understand what you're saying but from a practical point of view if I still lived in my old house with trickle vents I could fit one of these units and draw 35% of the air from inside the house and 65% from outside the house. I would not be replacing any existing ventilation just enhancing the ventilation that already exists. I think the confusion is that you are referring to a new ventilation system using one of these units and I am talking about enhancing an existing system which uses trickle vents in an older house.

I'm not explaining myself very well. Taking my house as an example. The bathroom needs ventilation at 7l/s, kitchen at 8.5l/s and shower at 3l/s giving a total of 18.5l/s to ventilate those rooms sufficiently. That leaves a requirement of 31.5l/s from the external vent to give the required flow for the heat pump. The four vents could be balanced to provide the correct flows. The rooms need ventilating at that rate and therefore heating whatever system is used. Most houses have trickle vents which would provide the required airflow into those rooms. It's not perfect by any means but for a lot of houses would be a good solution.

In our area in the summer when the sun shines, in the afternoon there is always a breeze. This helps to prevent a heat build up on the surface of the roof, therefore decrement delay is less of a factor. Unless your property is well sheltered I would be more concerned about heat loss. Presumably the room has good ventilation.

Wouldn't it be possible to have connected ducting for say three internal extracts and one external extract, balanced, so the internal extracts are extracting at the correct rate for the room type?

I have a natural immunity to tuberculosis from when I was a child, without feeling unwell, but I think it would be classed as a serious disease as would Weils disease as they are both potentially life threatening.

Do you know when the 10 years period starts from?

Hi, welcome to the forum. It's a great resource as you've found. Good luck with your build.