Indy

Thank you all for the wonderful replies and lots of interesting information. Some people picked up on the fact that I do want the best of both worlds, which is accurate. I guess what I was looking for is justification to help me pull the trigger on MVHR based on actual experiences. I will be blunt here and everyone I've spoken to including friends and family who've built new, done major renovations and retrofits - none of them have anything good or bad to say about the MVHR apart from the price. But they do at least say that they wouldn't change their decision to put the system in, so I guess it is one of those things that once you experience it - hard to go back to being without it. So on that track, I think I will stick with my original decision and go with the MVHR. And then plumb in for the Aircon system for the actual internal/external units to be added in a couple of years time.

Yes, comparing apples to strawberries is an apt summary as is the fact that I do want both. In an ideal world, both would get installed at the same time! The builder does fully understand the importance of airtightness and also what an MVHR system does and achieves, and how that compares against the Air Con. It was my pointed question at what he would choose for his own house when he said Aircon will give you the noticeable comfort, whereas MVHR is part of the fabric and not really that noticeable. Plus, our usage means we'll probably end up negating most of the advantages of the MVHR with the missus' need to crack open a window and let 'fresh air' in - blowing a hole through my airtightness layer! I guess a better worded question would be - is putting in MVHR a must have?

So our build is reaching the point where we need to make a call on whether the MVHR system goes in. Its a standard masonry build (block and block with 150mm cavity), silicone render on the outside and some attention paid to airtightness. We were all set on having MVHR, and have had a design done, posi joists laid, routes confirmed pending final design etc. However, in a conversation with the builder when I asked about Air con - his recommendation was to go with Air con over MVHR if there is a choice to be made. The reason is that the living areas and master bedroom are both South/West facing, and we have large vaulted ceilings in the master bedroom which may become quite hot and oppressive as the heat is trapped due to the solar gain. They will both cost in the region of £7k ish supply and install. I know people have done it cheaper when doing a self install and commissioning but that's not a realistic proposition for us so it would have to be done by the builder/subcontractor. He's actually been quite helpful and given me a week to make the final call, but it's put me into a bit of a tailspin and I've tried to summarise my thoughts below: MVHR (Pros and Cons) Can only do it when the walls and floor are open - so its now or never Avoid trickle vents in the windows (I don't like the look of them, but do I not like them £7k worth? Not sure!) Better airtightness No mould and condensation issues Some heat recovery though not enough to wash its face in terms of install cost (Capex) and running cost (Opex) So it's very much a 'luxury' good and a nice to heave. Expensive for something that most buyers wont put a value on (when it comes to resale time) Air Con More immediate and noticeable impact as we have a South/West facing garden and master bedroom which will get a lot of solar gain Works for heating and cooling so a reduction in gas usage for some months when air cooling/heating in certain rooms would be sufficient Probably more of a noticeable feature and buyers may put a 'slight' premium on it at resale time - though this is not an imminent event! Will make the house much more liveable in the warm summer months - and running costs will be further subsidised by the Solar PV and Battery storage My current thought process: Install MVHR (£7k) as its virtually impossible to retrofit cleanly. Put the power and condensate pipework in for the Air Con (£1k-£2k now) and the actual units in a couple of years once we've lived in the property and know what rooms to install it in. If you are building a new house, is MVHR a must do and has anyone built without one? What was your experience? TLDR: What would you put in, if you only had £7k to play with and were asked to choose between MVHR and Air Con?

Well this is all quite conflicting advice with what ChatGPT, Gemini and the vast majority of the internet sources advise. All the online searching I did discouraged me away from the ledger board approach and said the hangers must be built into the masonry for longevity. The ledger board is only held up using chemical bonds and that the weight of the floor above it would eventually work those bolts loose - especially as I'm using Celcon blocks (which can't be changed). So I spoke to the builder who has confirmed that he'll be using joist hangers built into the masonry. Much ado about nothing in the end - though I did get to learn something new I guess.

Can you enlighten a simple mind like mine how that would work - trying to learn all the different variants of putting joists up!

Too late for that - the ground floor blockwork is already in using the aircrete blocks and PIR. No plans to change it now as the materials for the first floor have also been ordered already.

Holy thread bump...... Coming to this thread as we’re in a similar situation. 2 storey (plus loft) house being built in masonry (Celotex 7.3kN high strength blocks) which will be rendered on the outside and wet plaster on the inside. Floor will be Posi-joists which I always assumed would be done using joist hangers. Spoke to one of the brickies/foremen on site who mentioned that they would be using resin anchors rather than joist hangers as it’s easier to level up using a laser level – compared to joist hangers. Not sure I fully understood it when he mentioned and spent the weekend reading up about it on ChatGPT and Gemini. The unanimous verdict was not to use the resin anchors into the Aircrete blocks as the fixings were going to come loose in the long term and masonry supported joist hangers are the way to go. Spoke to the builder / boss man who confirmed he was going to use joist hangers. Feels like a win but I’m not sure reading some of these comments. We are aiming for an airtight house with parge coat/wet plaster inside and silicone render outside. Is there a preferred way to go? I don’t want squeaks/mechanical fixings failing on me in the next 10-15 years.

Haven't changes to the planning system been announced almost every year or so - with nothing really happening? I'd love to see some action in this area so people don't have to wait years to get planning (4 in our case) but am very cynical that this is more soundbites with little action to back it up.

Freedomsat (through Viasat) is another option but it’s likely to be GEO, hence slower speeds and higher latency so not really a suitable replacement for home broadband usage.

OneWeb is the only other operational LEO service that competes with Starlink, but it’s B2B rather than B2C like Starlink. The terminals needed to connect to OneWeb are also an order of magnitude more expensive (enterprise grade) so its not really a competitor in that sense.

Prefer the first one.

Probably should have been made clear in your discussions re the work, our builder made it clear that there is extra labour and some fittings needed for wall hung/concealed stuff and the end price would be higher.

Very very rare that 3 showers would be used together simultaneously. 2 is more realistic and I'd like a good flow rate on both of them (15lpm + ideally).

Ours took 11 months - give or take a few days.

Ok, so let me restate the problem statement - which is very much in the vein of how do I make sure we never run out of DHW rather than unlimited hot water. Measured the flow rate of the tap installed for the builders using a weir cup (Arctic Hayes 888000 U Flow Water Gauge for Water Flow Measurement : Amazon.co.uk: DIY & Tools) and it easily saturated the 22lpm mark - so that means we should have excellent incoming water pressure (unless there's another way to check). This is the setup of what we're going to have: 5kW Solar PV array + 10kWH of battery Gas Boiler (plus gas fire and gas hob, but that doesn't matter too much) UFH on both floors - which will be designed to run at lower temps for a future swap out to ASHP (say in 5 years or so) Assuming unvented cylinder - 400l 3 full bathrooms with showers + 1 guest WC Talking about the issue with the missus, she thinks I'm overthinking and overengineering the solution for a problem that will occur at max once a month - when we're all in a rush to get ready. Most days, the kids shower in the evening and both of us do it in the morning and even then it's staggered. ChatGPT presented us with a solution which is very much in the vein of talk to a plumber that designs a priority DHW solution. I like the idea of having something like an immersion heater in the cylinder which will allow the hot water to regenerate in 10-15m, rather than waiting an hour for the cylinder to replenish.