joth

It may have been Peter Warm's blog actually: http://www.peterwarm.co.uk/10-most-common-phpp-mistakes/

Welcome to the scope creep! @Ferdinand summed it up so well for me here:

Oh and to add a smaller point, are you comparing pre or inc VAT prices? The ASHP should be 5% rated vs 20% for the oil boiler (AIUI)

The RHI compensation angle? With a ~11kW heat load expectation, you should get at least £7k - probably more - in RHi. Over 7 years.

Remind us if you're in the exorbitant SE? Did it include a large unvented cylinder and plumbing and buffer tank and stuff? For just an ASHP that's way to high but I find they tend to assume a lot more in the quotes and yes, that sort of "ball park figure" is very typical for first contact I made with 3 or 4 suppliers around here (Herts). Obviously MCS certified etc etc and obviously like every other part of a build can be undercut if you're happy/able to DIY install.

Thanks @AliG and @Russdl Sounds like if we put in the duct or grommet there's a reasonable chance they can use that if I leave the installation until late on. Snag is my electrical cupboard is not in a brilliant place to get an external duct to (in the middle of the house upstairs) so I either need to get my hands on some of their cable before/during first fix, or accept the box goes somewhere else. Either way the consumer rather than new development route sounds workable.

Key thing is what are the pipes embedded in, underneath the amtico? Assuming it's a large mass of concrete, it will have a high heat capacity you need to pump a lot of energy (warmth) it to warm it all up before you'll start to feel much coming up through the amtico. Whoever has the lowest floor flat (ground floor, or basement if there is one) will likely have slower warmup reactions and overall need to keep the UFH running longer (more total kWh spent) because the underside of the concrete will presumably be colder than all the other floors. It's possible (if unlikely) that someone actually specified the ground floor UFH a bit differently to handle a higher workload. Also a common design in larger blocks would be to put the common services & communal boiler etc into the basement, which helps offset that issue a bit.

Thanks for this! Although for us there's actually no problem about BT line, we already have one of those 🙂 it's specifically the Virgin Media install that I'm struggling with as their two options seem to be unobtainable (New Developer Route) or unacceptable (consumer install, with a load of cables traipsed over and a holes cut into the outside of the house). This is a good option, and I might well do this anyway as we're due (they say) to get FTTP in 2-3 years. The risk I see is VM (and Openreach for that matter) seem very particular about new installs only happening via an external termination box that must be hung on the side of the building an access through the wall so would be unlikely to allow use of it. Also, VM will only route the internal signal via their own specially endorsed RG6 cable, and so if we want TV outlets in various rooms I need to get my grubby hands of a good amount of this magic cable. But that said, this all gets much simpler if I accept we'll never put wire VM cable to multiple TV sets. (I've never even subscribed to cable or satellite TV in my life, so it seems very low likelihood I'd ever want it to multiple receivers around the house).

Revisiting this old thread, can I ask when you placed the order and at what stage the installation happened? e.g. did you just complete the build them call them up to have it installed? I'm reluctant to do this later on through their normal consumer ops because their engineers will drill holes all over the exterior of the house destroying all the effort put into airtightness. But if they arrive too much before first fix I can't get them to put cable into the various points I'd like it. Ideally I would do this very early on and just have them leave a big reel of spare cable that we can put into the various rooms ourselves during first fix, and likewise we can make the airtightness fixes needed to deal with their initial install. I'm just not sure the consumer-focused engineers will do this. But if they will, I'll probably just pay for a rolling contract for 1 month, just to get the initial cable put in, which we can the bury) (I've briefly explored their New Developments process, but that seems an impossible option; only interested in large MOU not a single house renovation)

Honestly, I have difficulty convincing myself of it, but there was a lot of data thrown at me last night showing the point. (Based on survey from last month of the national average CO2 costs of acquiring pallets vs generating electricity during the heating season. Obviously any given individual's mileage will vary). I can't find the reference now of course, I will request it. Best I can get is this which backs it up (factor 7x more CO2 for ASHP) but it's well out of date.

I know it's OT for your question here, but if you're looking at a secondary heat source have you considered biomass? That would seem more complimentary as it can remove the dependence on electricity supply (or at least, on electriciry pricing), is better suited to large buildings with lower levels of insulation and rural settings, and has a lower effective CO2 cost.

Other thing to confirm is that you have planning approval for the external unit? It can be done under permitted development, but only if it is only used for heating not cooling

Any idea why not 20% ?

Full disclosure: after a lot of back and forth we're not getting three phase, keeping with the existing single phase and a G99, so I no longer have any "skin in the game" if I've misinterpreted anything

https://www.gov.uk/government/consultations/smart-metering-equipment-technical-specifications-second-version Page 87 "Consumption shall be the sum of the cumulative Active Energy Imported on the importing measuring element(s) of its Electricity Meter less the sum of the cumulative Active Energy Exported on the exporting measuring element(s) of its Electricity Meter;" I.e. you just add up all the import ever and subtract all the export ever to calculate total consumption. There's also a YouTube video where someone got hold of a decommissioned non-smart 3ph meter and empirically tested it works the same way. However the meters are highly configurable in this (for residential Vs commercial and for different country needs). Talking to a phone support at my supplier, he couldn't vouch for how it was supposed to work, but knew for a fact they generally get it wrong first time and have to send an engineer out to fix it after the customer complains.