Marko

I've gone down this rabbit hole, and I have an ASHP. I came to the conclusion that it's probably not worth it. Buying the gear, then fitting it and plumbing it up, then who knows how effective it would be. Instead, a mini split system probably works out just the same, or not far off in the end. Bought and fitted for 1.5-2k, or you can buy the pre-charged ones for £5-600 and do it yourself.

I doubt this house had any radon barriers, but MVHR dropped Radon levels: https://www.heatspaceandlight.com/mvhr-lowers-radon-levels-cotswolds-cottage/

Not sure if you're on about the ducting supply and exhaust air (house side) or the supply and exhaust (external). Regardless, there's always the risk of condensation in the winter. In the summer my loft space is gets extremely hot so I have individually insulated all ducting (house side) with ISO sleeves as well as 300mm loft insulation on top. Just belt and braces to avoid the house overheating (even with summer bypass). I don't know if that answers your question.

Yes, you can feel a very slight breeze on a back of your hand under the door when closed but it defiantly shouldn't be whistling through as others have said. Sounds like its not been commissioned properly in terms of correct flow rates and balancing. Mines fine and I went with lower flow rates from the previous versions of Part L after reading through a lot of info on here. Best thing you can do is do it yourself. Calcs are straightforward and you can hire an anemometer for week.

Just send your floor plans to BPC Ventilation and they'll do it for you and provide you with flow rates. That gives you a good starting point. Just an FYI from what I've learnt along the way (some may disagree/correct me): Kitchen extract should ideally be located above/adjacent to the sink, not the stove. All plenums should have a minimum clearance of 300-400mm from walls. If your floor joist permits, try to locate supply valves above/adjacent to the radiators in the bedrooms and other living spaces. Apparently, this helps with convection etc. They say locating the unit in a warm room rather than a cold loft is better in terms of efficiency. I've not had any negative experiences yet though. Don't underestimate the work involved if it's a retrofit and you are slightly OCD.

@low_and_there which method did you eventually go for? I've got an almost similar scenario to address.

I’m not too sure. Most appear to just lay the bare ducts under regular loft insulation 300-400mm. I wanted to get mine up and running prior to getting the loft insulated. I also thought it would be good practice to lag the ducts in case any loft insulation became displaced in the future. I got mine from BPC: https://www.bpcventilation.com/iso-sleeve-pipe-insulation

Mines in the loft. No where else to put it really. Might end up ‘cladding’ the sides with PIR, at some point. On the coldest day we had last week, the temperature difference between the room extracts and supply valves was hovering around 0.3-0.5 degrees. There’s no insulation in the loft yet either, but ducts are lagged with 80mm ISO sleeve.

It’s currently-2 here. What’s peoples indoor humidity readings been like? We’ve had our system operational for around two weeks and I suspect various elements have been drying out over that time. We’re sitting at 55% at the moment.

Thanks for the insight. I’ve been looking at carbon filter solutions on here, seems most diy them. The house isn’t particularly airtight at the moment but it’s a work in progress Yes, I’d be looking at direct air with a duct to either outside or from under the suspended floor.

That window is north facing. No none else in the street seems to use their chimney. What do you reckon?

Thanks for info both. The intake, on the left is fairly close to the chimney so unsure what to do. Might be that smoke blows over and past.

I live in a standard terraced house, and my MVHR intake and extract terminals are located about four tile courses below the ridge on the side opposite the chimney. I am considering recommissioning the existing chimney for a wood-burning stove, and I am concerned about whether smoke might be drawn back into the house through the MVHR system. If anyone has dealt with a similar setup, I would appreciate any insights into whether its worth the hassle or not.

Am I right in thinking that going of Approved Document F, you go with the higher flow rate value of either paragraph 1.24 (A minimum rate of 0.3 litres per second per m2 of internal floor area)....or table 1.3 (Minimum ventilation rate by number of bedrooms (l/s)). In my case: Paragraph 1.24 requires meeting both 0.3 l/s/m² and the bedroom-based flow. For my area of 58.4 m², 17.52 l/s is needed by floor area, and 25 l/s by bedroom count (two bedrooms). So, I must use the higher value: 25 l/s. For boost, I was planning on upping these by 20%. How does all of this sound?

Fantastic. Very much appreciated!