I was hoping for some advice after reading about people having issues with their 9kw Diakin unit. Octopus are also installing an Eddie and a 300l Diakin water cylinder.
My heat loss survey came back of 7.74kw and they are wanting to replace all but one radiator in the house. All piping to the rads is 10mm which they didn’t seem to have an issue with.
They are wanting to install it at the end of the month, is there anything which stands out as being wrong?
We currently have a 4kw solar array and an ev.
I’m rather new to all this so seeking some third party advice!
Not enough information for us to know the accuracy but for a 4 bedroom house your heatloss seems a little high but it will depend on the build and the insulation you have installed.
Do you have cavity wall insulation, how deep is your loft insulation?
The 9kW unit is a beast and I would personally recommend double checking the heat loss survey (even if it is just on upgrades.heatgeek.com) to make sure you are not under 7kW (the limit for the smaller 8kW unit (actually Modulates and seems to run a lot better during the shoulder months).
If you do not yet have 400mm of loft insulation, cavity wall insulation or internal wall insulation and double glazing I would highly recommend these first (cheaper to insulate than to keep letting the heat out).
Eddie is the solar diverter immersion heater? Is that useful these days? I thought you were generally better off importing cheap-rate overnight then selling solar back to the grid during the day. That’s certainly what I do.
I’m in a similar sort of place, but post-install. 3 separate heat loss surveys all said heat loss around 7.5kW, though heat geeks predicted much less. There’s a heuristic based on degree-days to calculate based on gas usage - I think there’s a link in the learning resources topic?
It’s a little early for me to report on 9kW performance. Have not been impressed by its defrosting behaviour, but I’ve been making tweaks and may have got it tamed.
Very unimpressed by poor reporting of consumption/generation. I repurposed one of my Zappi’s CT’s to measure energy consumption.
In my case my Octopus journey took months while finding the most suitable solution. I think it was time well spent.
In my view, I think you should spend more time researching whether you need the larger Daikin. My heat loss was first surveyed at 9kW and I was allocated an 11kW heat pump.
After a lot of to-ing and fro-ing ( including having figures from a blower door test replace the MCS assumptions) my heat loss was adjusted to 7.5kW and then I had an 8kW Daikin fitted.
As it happens, in this present cold weather (which is about at the design outside temp). I am finding that about 4kW of heat from the pump is enough to hold the house at a steady internal temperature.
So, my impression is that MCS calcs over estimate heat loss and lead to larger-than-needed heat pumps being fitted.
You will have read in these pages that there is a world of difference between the 8 and the 9kW Daikins, so in your place I would ask for a delay in the install schedule while you do more research.
Having a heatpump is way better than heating by gas boiler, and all of us here want you to get it right from the start.
If you have smart gas meter readings for the past week and you have maintained a fairly stable house temperature that would be a good start to sanity check the estimated heat loss is in the correct range.
I have called octopus to see what they can advise, it seems like delaying the install is the sensible option here.
@divenal - I am on a old FIT Tarrif for Solar, so they are installing an Eddie so all excess solar is used for the HP. I don’t have batteries installed yet, these are next on my list where I will switch over to a solution like you are using. I am interested how you are finding your HP compared to your previous gas system.
@dmajwool - Thanks for your advice, I have done a lot of reading around here and come to the same conclusion that the 9KW HP isn’t going to be the best solution for me. I have requested that they delay the install so I can seek further advice.
@matt-drummer - Thanks for your input, I have read many of your comments over the forum with this HP and the struggles which you have had. Outside this forum, there isn’t too much information kicking about around this. Thank you for assisting everyone, you certainly may have saved me hassle in the future! I will mention about the Rads not being big enough to Octopus, or are you saying that I should look for another company? If so, are there any recommendations?
@Ringi - Is having a 40c design better than a 50c one? I had no input in what is getting replaced, however the engineer who done the VERY long survey seemed to imply the rads they were installing were plenty big enough. This is all rather new, and I would love some additional informational information!
Some raw numbers:
Current heating / water solution - Gas boiler with tank (approx installed 1998). We also have a 5kw wood burner which gets used for heating the living room. We have only started utilizing central heating from 2024, and it isn’t on all year round. Only a handful of months a year.
I’ve not had FIT myself, but my understanding is that the FIT payment is in two parts: a generation component and an export component. The latter is “deemed export” by default, but you can choose to change to measured export without affecting the generation component of the payment. I have read various people reporting that they are better off on measured export, since they can get that at a higher rate per unit. eg 15p from Octopus.
The house is definitely more comfortable, with a much more uniform temperature (when I’m not fiddling with the settings…) We used to let house cool overnight and reheat overnight, but that’s not the HP way of doing things. (Plus with cheap overnight electricity, makes sense to boost, rather than cut, the heating overnight.)
OH approves, which says a lot…
I’m much more aware of energy consumption - previously I hadn’t really thought about gas consumption between bills, wherease because of solar/battery, I do tend to keep quite a close eye on electricity consumption. So a bit of an eye-opener during the cold snap over the last week, but of course that was anomalous, and I don’t have comparable gas figures. I should ask my neighbours how much gas they’ve been using, I guess.
This is a real positive that comes out from providing metrics - even like a basic In Home Display.
If we can get people to engage with energy consumption, I think it is natural behaviour that they try to optimise. This is great news for reducing carbon emissions
Chapeau to OEM for providing us with all these facilities.
A lower flow temperature will give higher efficiency (COP) and hence lower running costs. So I consider 50c can only be justified when it saves a lot of capital costs.
I have Octopus coming on Thurs to see whether they can fit the 8kw unit instead. I will also mention the 40c flow to them when the engineer is here. They couldn’t answer the questions over the phone.
Hi Dan,
The non-technical element that’s involved here is the BUS grant.
If you want Octopus to be able to claim it and discount your bill then they need to warrant to MCS that MCS rules are satisfied. So in many ways Octopus’s hands are tied about the size of pump they can offer you.
If you can convince them that your house has a total heat loss different than the standard MCS spreadsheet, then that should take precedence over the assumed values.
In my case, I checked with MCS (who were very helpful) that my blower door test result CAN be used to over-rule the assumed ventilation losses from my 1980s house. This downward adjustment to the heat loss was enough to put me in 8kW Daikin territory.
But it’s not enough to just say “please”.
If you don’t want the BUS grant, you can do whatever you like.
Having said that, I’m sure that as Octopus gather more performance data from their installations they will get a handle on the correlation between MCS heatloss projections and real-world usage.
In my case, the 7.5kW MCS figure corresponds with actual heatloss of around 4kW during this cold snap at more-or-less design conditions.
So I would like to assume that Octopus (and other installers) will now be more comfortable at specifying systems with much smaller heat pump capacity surpluses.
All the tinkering I’ve been doing is aimed at running the heatpump lower and lower.
They seemed pretty confident with being able to install the 8KW one (Cosy or Diakin) and are going to review whether the Rads are big enough and to check if I can have a 8kw one.
They mentioned the HL had my insulation down as 100mm when I am pretty sure it is all 300mm.
EDIT: The support guy may have been mistaken, I can’t see any option for the Cosy 8 online. He was either mistaken, or they have one which they haven’t published yet.
