Renewable Heating Hub Forums - Recent Topics

Nook batteries from Octopus

Tim441 — Mon, 22 Jun 2026 14:46:16 +0000

Octopus have launched Octopus Nook Cube, a compact, shoebox-sized 2kWh battery that simply plugs into a standard socket. Controlled through the Octopus app, extra units will be able to be added to increase storage up to 10.5 kWh. For homeowners, Octopus is also launching Octopus Nook Collosus, a wall-mounted 5 kWh battery, which can be stacked up to 30 kWh for larger homes. Both battery systems are compatible with solar panels and come with a 12-year warranty. available from next year.

No idea if you can have these alongside any other batteries?

https://www.renewableenergymagazine.com/storage/octopus-energy-launches-the-a-nooka--20260622

vaillant arotherm plus - Failure - DHW

trebor12345 — Sun, 21 Jun 2026 20:31:44 +0000

Our 3 week old vaillant arotherm plus has failed in DHW mode. The UI shows the following faults:

Connection fault Frequency converter not recognised.

Domestic hot water compressor blocked.

I have tried a reset on the controller and powered down both controllers and the heat pump. No effect!

Any thoughts.

Adding additional Solar Panels to a DC coupled battery system

bontwoody — Thu, 18 Jun 2026 16:28:22 +0000

I am currently in a position where it would be very easy to add additional solar panels to a lean too I will be constructing in the near future.

I have a 2.66 kWp FIT system which has been supplemented by a 4.6kWp East/West oriented system DC coupled with a 10kWh battery and 3.6kW inverter.

The battery and inverter are Huawei and the panels have optimisers.

The extra panels would be West orientated and would be very useful in the winter. Their extra output, probably wouldnt make any difference to my peak output and would be clipped by the HUawei inverter anyway.

Is this a sensible thing to do? Would I have to notify anyone? Would I be better trying to source another battery module instead?

I seem to have a spare MPPT on the inverter so Im assuming the new panels are just in a single string with the optimisers doing their thing?

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Or would it be simpler to buy a balcony solar system and plug it in when required??? :-)

Thanks

Four Heat Loss Surveys, Four Different Answers. How Do I Choose the Right Heat Pump Size?

AnnaB — Wed, 17 Jun 2026 09:27:50 +0000

We are installing an ASHP at the same time as doing a house renovation/extension. We live in a 1950's detached 3 bed, but will be doing a 2 storey extension and it will become 4 bedroom. There are 5 of us living in the house. I have been researching this for months and feel I have approached 4 reputable companies for quotes. They have all been and measured (where they can, as extension is still only plans) and issued estimated heat loss reports, although one company has not issued the full report as they say we would have that on receipt of a deposit.

My problem is that they are vastly different in terms of estimated heat loss, estimated energy requirements and then the recommended heat pump size. The lowest heat loss given is 5.67kW at -1.5degrees and they recommend a Valiant Plus AroTherm 7kw. Another company has also suggested the Arotherm, even though their heat loss estimate is 8.41(also at -1.5 degree).The highest is 9.98kW from a company suggesting we get a Mitsubishi 11kW, however they have calculated this at -3 degrees, which I feel is an over estimate. We have also had a mitsubishi Ecodan 8.5kW form a company who estimated the heat loss at 7.99kW at -2 degrees. I am very confused! Can anyone offer at suggestions on how to choose?

We have also had very different estimated heating requirements ranging from 12,344kwh to 18, 579kwh. I am presuming that this is partly due to the different estimated heat losses, but what other information should they be using to calculate this? They have all given the same estimates for hot water requirements, but even so, they seem to have all based this on 4 person occupancy, whereas we are a family of 5.

I'd be really grateful for any advice on how to proceed. Many thanks, Anna

Floor standing brackets for K3 rads

Singlespeed — Mon, 15 Jun 2026 20:48:29 +0000

My neighbour is a plumber and said I would need to fit dwangs (reinforcements) behind the plasterboard to hang big enough radiators for my retrofit. He was unaware of the floor standing brackets from Stelrad.

I originally saw them on cityplumbing at over £60 which I thought would be a pair... but that's each. Stupidly, Wolsley are basically the same shop in the same building with the same stock and we're 1/3 of the price!

https://www.wolseley.co.uk/product/stelrad-k2-k3-freestanding-foot-single---hardware-pack

https://www.stelrad.com/wp-content/uploads/2014/08/Stelrad-K3-Floormount-Instructions.pdf

With some careful measuring to position the height of the wall brackets, the radiators are stood on the floor but still hooked onto and restrained by the wall brackets.

The 700 x 1600 weighs 96kg when empty.

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Harvest Thermal - ASHP with a smart thermal battery

springswood — Mon, 15 Jun 2026 17:11:08 +0000

I thought people here might find this interesting, even if it is a new US company so probably not available here for a while, if ever. I need to think about it for a while to decide on the pros and cons compared to using electric batteries.

The idea is to use the ASHP to heat a large water tank. The minimum they work with is 300 l, so roughly 10kWh. The ASHP feeds hot water in at the top so it's stratified and stores a variable amount of heat energy. The new bit, called the Harvest pod, connects to the heat store to deliver hot water, there's also a heat exchanger to transfer heat to radiators or underfloor heating. Diagram below.

The claim is it can cut bills by 30%.

The smart bit is that it looks at your usage patterns for heating and hot water and the weather forecasts to determine how much energy you need and when. It then supplies that heat into the tank by running the heat pump at the most efficient times taking advantage of higher air temperatures, time of use tariffs and solar PV where it can.

It was developed by a married couple of engineers in California when they put in their own heat pump. Though one of the advantages they have is that their renewable electricity has a lot of solar, meaning electricity is cheap when the air is comparatively warm.

I found it on YouTube here Harvest Thermal at Amply Energy It's an exceptionally clear discussion with an amazing lack of waffle. The designer really knows her stuff and the podcast hosts are good on both heat pump technology and the needs of installers. A word of warning though, it's very American full of unfamiliar terms and archaic units, Fahrenheit, BTU's, Gallons (presumably US not imperial).

Their website it pretty good too Harvest Thermal Amongst other things I found this general schematic. They did mention it also works for 'European style radiators'.

I'd be interested to see what anyone thinks. I suspect it may seem dangerously similar to the dreaded buffer tank...

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Hypothetical House Design

chastity_outward053@simplelogi — Mon, 15 Jun 2026 06:18:26 +0000

Looking for some advice - planning a self build - but at the early stages such that a lot of this hypothetical at the moment (we don't have exact floor plans) and therefore exact heat calcs.
However I am looking more for advice on the layout of the system.
It will be a house to PassivHaus standards, we will have a ASHP.
I will be running KNX throughout.

Looking at UFH with 10 loops in the concrete slab, and for the purpose of this lets assume all 10 loops are done in ridgeline eco max 22mm pipework, and have a length of 50m each (so 500m total, with a total water volume of 108L.)
The loops will all be controlled with Salus THB23031 auto balancing valves, and a UPM3 circulator pump.
The plan is to run this as an open loop, on 24/7, on WC. The auto balancing valves will throttle (or not) to maintain a deltaT across each individual loop (will not be zoning with them - all open all of the time).

ON top of this I will have a series of 7 fan coil units - for arguments sake lets say Dakin - FWF03DT.
My plan at the moment is to use these as trim heating or trim cooling. The FCUs will tee off the ASHP flow, have a zone valve, a magna1 circulator pump, split into 22mm pipe work for the runs, each FCU will have a PICV valve.

The exact strategy I have not yet worked out but anticipating something like this:
During heating season - UFH does the bulk of work on the WC, if the temp drops below setpoint -2, modulate PICV and FCU fan in that room to give some top up heating. I am anticipating this being unlikely during the winter in a passivhaus.
During the cooling season, as the heatpump hits the low end of the weather curve, switch into cooling mode. Run cooling at worst case dew point + 2. Apply a large moving average to this calc and only update every 5 mins or so (using KNX bridge to talk to ASHP) to avoid hunting and drastic changes.
Use UFH to cool the slab. if room with FCU is setpoint +2 modulate PICV valve and FCU fan. I anticipate this to happen more often, due to solar gain and the lack of efficiency cooling with a UFH slab.

I have been trying to do due diligence with the plumbing layout. I have had one ASHP with a buffer, and my most recent without.
I have read/watched plenty of information on the pro/cons of buffers volumisers etc. But have not been able to get my head around whether this is a case where I should be looking at them or not.

So assume worse case flow rate/volume for ASHP, as the system is above, plumbed direct.
This is FCU zone shut - all auto balance valves fully throttled (but importantly that is always CP -0.3mm on the stroke of the actuator). I have estimated this drops the flow rate per loop to around 0.6L/min . Giving a total flow of 6L/min in the system, and a volume of +108Ls.

Looking at valiant arotherm plus 5kW requirements (min flow 400L/h, min volume no back up heater 40l) I easily exceed the volume requirement, but I am below the 6.67L/min requirement (albeit only just).
I have ballparked guessed the 5kW for the passivhaus as I am not expecting big heating loads, this becomes even worse if I upsized to the 7kW (9l/min) or the 10kW (16.5L/min).

The other end of the spectrum, lets assume we have fully opened UFH valves, (relatively short loops, with a large, for UFH, diameter) we may achieve 30L/min on that loop. Lets assume that the 7 FCUs all turn on, so zone valve opens and PICVs start to modulate - for the FWF03DT, highest flow rate is 568L/h (heating) or 515L/h (cooling).
which gives 7 x 9.5L/min or another 66.5L/min.

Now I know the chance of all UFH zones being fully open, and the FCUs running full whack simultaneously is extremely unlikely - however I want to discuss the case as it is possible - the house has been empty for a while, we came back when it was truly cold and the heating had previously been off?? I don't know, but I want to understand what would happen hydraulically.

So this gives a total flow rate of 96L/min and a system volume in excess of 108L + FCU pipework/coils etc.

The volume is not an issue, but on the 5kW the max flow rate is 14.3L/min. on the 7Kw it is still only 20L/min.

Now even with more sensible assumptions I think the UFH could exceed or approach that on its own, and even if the FCUs were ticking over slowly, I think I would be way over the 20L/min.

Which brings me to the crux of my question - would a buffer be required? I appreciate distortion/mixing makes it normally a no/no. But hydraulically I think I am likely to be at the bottom end of the heat pump flow rate for the majority of the time (ie UFH is stable, nicely at temp, the balance valves will be mostly throttled, and assuming I will be in the region of around 6-10L/min) the FCUs however can demand a significant flow rate if they want. especially given that I am running them both cooler (for heating) and warmer (for cooling) than their design point.
Do I need the hydraulic separation that a 4P buffer provides, and if so is it worth going large, like say 200L to provide the ability for it to stratify?
Or another option I have looked at is including a 0-10V belimo ball valve as a bypass valve. Have a flow meter on the ASHP return with 0-10V output, and using KNX to proportionally open the bypass as the flow rate approaches the minimum ASHP requirement, which fixes the low flow rate issue, if I opened it at the other end of the scale, would it also fix the high flow rate issue. Obviously at the expense of efficiency, but only in the shoulder cases as it opens, and not permanently like a 4P buffer (with mixing/standing losses etc) would.

Another question I had, is there any disadvantages to having a 50L or so volumiser on the flow line, despite being above min volume, if I could absorb some of the cold water prior to the slab on defrost cycles, that seems like good thing.
Yes it would give me slightly more standing losses, and it would add a lag into the system, but for an open loop 24/7 WC plan, I don't see this being an issue in a passivhaus?

Sorry for the long post, if you have any more questions just ask, I know some of this is over engineered, but I do enjoy that side of it as well!

Helium heat pumps

Billsp44 — Sun, 14 Jun 2026 16:14:57 +0000

I am about to install a heat pump in my 1930s detached house. However my mains gas Vaillant combi is only 7 years old and still going strong… Should I wait for this?

https://blueheartenergy.com/bouw-en-installatie-hub-blueheart-energy

BUS uplift to 9k for off grid installs. I can't establish if new builds are specifically excluded.

jimseng — Sun, 14 Jun 2026 12:21:44 +0000

Hi.
The BUS grant for new self builds is pretty straight forward - if it is a self build you are entitled to the full 7.5k BUS, even if you are not replacing a system but installing from new. The 9k uplift for off grid properties is coming in July and I am trying to establish if it is applicable to new self build properties too. The wording seems the same as for the 7.5k BUS, it talks about replacing existing systems and new self builds don't get discussed. Does anybody know what the situation is? Can anyone point to a specific document that says new builds are only eligible for the 7.5k BUS? I could easily opt to put an oil boiler into my new home as I am not on mains gas here so I wonder if the incentive applies to me to. As mentioned in another post I have already had the 7.5k grant offered but it has elapsed as it was 6 months ago.