MortarThePoint

Was that for >300sqm then or did you get the eBay price even lower than £4.75/sqm+VAT?

Interesting and very helpful, thank you. The whole pricing thing is really opaque and leaves me permanently thinking I'm left paying over the odds. I'd prefer greater transparency, but the closest I can get to that is SPONS and that has never been more out of date than under the current climate. I can remember when I first got my trade account at Jewson, I walked up to the counter with an arm full of plumbing fittings and the woman at the till punched in some numbers and gave me the price that was over double Wickes. I said that and she said that it was Osma fittings etc and that's much better than Wickes, though she would take a look and it came straight down to a bit under the Wickes price. I had naively hoped that having a trade account meant the end of the haggle, but how wrong I was.

FrameTherm sounds like a good choice, I've also seen FactoryClad is a lot cheaper, but may be difficult to cut to width. I'm taking a look at Actis Hybris which I have to admit to being a bit sceptical about. I need to understand it a bit more, but I might be being a luddite.

Have to taped the batten though?

@ProDave What's this bit?

Thanks. I have seen the long lead times but thankfully none of it is urgent.

It is for between (and below) rafters. I haven't had a price yet for FrameTherm but hope it may be my saviour. I spoke to a merchant a couple of years ago who said lots of people staple Loft Roll between rafters ? I don't think that's a good plan

Is Mineral Fibre rafter insulation always so expensive? I've been quoted £18/m2 for 100mm Knauf Rafter Roll 32 and that just doesn't make any sense: Same seller sells 100mm Dritherm 32 for about a third of the price per m2 (£6.70/m2). That's a performant self supporting product as well. The same seller lists 100mm PIR which is 50% more performant for £12.91, so cost per performance, that's less than half the price of the Rafter Roll. You'd expect to pay a premium for the thinner more performant product. All other applications, Mineral Fibre is considerably cheaper than PIR I have spoken to Knauf Technical and they can't comment on pricing. FrameTherm is also recommended for the rafter application so I am looking into that. Isover Metac seems to be similarly expensive. I don't want to use PIR or XPS due to the chemical content. I know that divides opinions, but can anyone recommend a sensibly prices alternative to Mineral Fibre.

Sorry I confused now. You had 1m3 for £900 and 2.3m3 for £444. Those aren't per me prices are they?

That's a good price as most companies I have spoken to have a minimum price (aka 'get out of bed price') much higher than that . The companies I am talking to (nationwide, I'm near Cambridge) have an things along the lines of 'Initial charge 2m3' of £1200 and then a per m3 price on top. Are you using a small independent contractor? That price is remarkably good.

Gulp! You've a commendably philosophical outlook @oranjeboom

Did the mesh get pulled up then or the pipes detatch from the mesh?

Still living through this nightmare. I wish I'd gone with a pipe with an Aluminium layer as they seem to flex and hold better rather than coiling back up. Is that correct of 16mm Pert-Al-Pert? I can use screws upstairs where there is no gas barrier, just the green sheeting. Downstairs I can't though. Nu-Heat sent a decoiler but it doesn't really help. Does Wunda's 16mm Pert-Al-Pert pipe flex and hold?

Nice. I've used their flow sensors before and know the company to be reputable which is important

Nice. I've used their flow sensors before and know the company to be reputable which is important

I need to install extractor fans anyway so the trickle overhead is small there. That's a lot less involved than ducting to a centralised unit. I don't want this to be anti MVHR as I think it suits many well. Personally: - I don't like all the ducting of MVHR. - I don't like the expensive single point of failure of MVHR - For my situation I don't believe the economics of MVHR work. Across 6months of heating season the average dT is about 13C and so the PIV annual running cost is £172 electricity. MVHR only about halves that due to its fan having higher power consumption. Even at £172pa the payback time would be looking like >15 years, based on a modest £2500 outlay. I suspect there are other annual costs that raise MVHR to costing over £100pa to run, taking the payback beyond 30 years. MVHR is largely about the heat recovery. What would you do if you ignored the heat recovery part of it? Sell me on MVHR without mentioning heat recovery ?

It's a very interesting read. I've wondered about how to improve air circulation between rooms, even thinking about incorporating small fans into the bedroom walls to move air to/ from the hall. Children like to have their bedroom doors open at night and from an AQ perspective that's really good.

Gosh those values are very high. MVHR will help with those greatly. I'm looking to go a different way myself but similar principle

I'll need extractor fans in the usual places and they will provide good 'leaks' I'm considering having them as dMEV too. I spoke to my SAP assessor and he thought it would be OK from the SAP perspective. My BCO has PIV in his own home.

Why not? Both draw fresh air in from the outside. MVHR distributes it better and does a better job of reducing energy waste but they are performing a similar function.

Sorry Peter missed your post. Ventilating an attic is normally a good thing isn't it

There is a lot of focus on PIV not being as good as MVHR on the heating bill side, which is only one dimension of this and I alluded to accepting that MVHR suits many so I'm more interested in people's thoughts on the other concerns. PIV Pros: Clean (filtered) fresh air blown in contributing to good air quality (AQ) No need for window trickle vents Controllable flow rate so can potentially be put into an AQ feedback loop No duct work and only one vent Low cost and low maintenance PIV Cons: Not as energy efficient as MVHR Many not distributed the fresh air as well as a ducted system Fabric condensation risk below 8C outside temperature ?more of a Timber Frame concern? Draught concern (if I was making a homebrew one I would include an ASHP powered radiator or the like) I am considering adding dMEV into the mix which would then greatly reduce the amount of air that is exiting via the fabric as well as improve bathroom dryness

Sorry for so many posts, but the picture is forming slower than I'd like Looking again at that unit (Blauberg EC S5B 270 £1250) it consumes a lot of power and it all looks to be fan related (i.e. no resistive heater or heat pump). Comparing it to a PIV system: PIV at 60l/s, dT=13C P_fan=20W, Q_heat=780W --> P_heat=260W (based on COP=300%) TOTAL=280W MVHR at 60l/s, P_fan=150W, Q_heat=780W*(100%-87%)=101W --> P_heat=34W TOTAL=184W So at an outside temperature of 6C that MVHR is saving you about 100W of electricity over PIV.

That was a pretty weedy and cheap system. Looking at a more expensive Blauberg unit the numbers are better (below). The blue shaded text suggests the efficiency is quite flat with outside temperature, varying much more with flow rate which makes sense as that is what impacts the 'thermalisation' time. Blauberg EC S5B 270 £1250

Thus far I have only found the graph below which is in someone's academic thesis and based on Stockholm where it is much colder. The temperature transfer efficiency is looking pretty linear and taking it as 87% at -4C and 95% at -16C it would be about 80% at 6C. These curves are suspiciously absent from the sales literature of MVHR systems though to verify. Blauberg Komfort Ultr 64-72% I can see heat recovery efficiency vs flow rate: