Renewable Heating Hub Forums - Recent Topics

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.

Heat pump design review please: 5 kW Vaillant aroTHERM Plus heat pump

ragtime27 — Sat, 13 Jun 2026 15:23:43 +0000

Hello all,

I have received the heat pump design from eon after 6 weeks of waiting

here's key points:

The estimated heat loss is approximately 3.92 kW. with proposed a 5 kW Vaillant aroTHERM Plus heat pump. This sizing is based on continuous heating (24/7 operation) and does not include spare capacity for intermittent heating or temperature setbacks.
A 250-litre Vaillant hot water cylinder is included in the proposal and is to be installed in the loft space, subject to a suitable base being constructed by a third-party joiner and approved by a structural engineer.
Two radiators are proposed for replacement

The proposed system flow temperature is 50°C for -1.7°C(London suburbs)

scop 3.41

TRVs are proposed to be removed from all radiators to ensure sufficient water flow through the heat pump system. This helps support defrost cycles and improves overall efficiency in line with an open-loop system design.

Upgrading the existing 15 mm mains cold water supply is not included within the scope of the heat pump installation.

is the temperature flow 50°C quite high?

Can I insist on lower design temp?

primary pipes 28mm branching to 22mm then 15mm to the rads

no UFH, propery is fairly insulated.

is it a haggling process with eon since they can swap up to 60% of rads

also, the existing water tank and the header in the loft seating just above a bearing wall.

my concern is getting a structural engineer to calculate the load, only to tell me that it has to go where the existing tank is seating.

what the solution here, do they need to swap and putting the cylinder, however platform is needed beforehand.

have i missed anything

I have attached the design proposal

Many Thanks

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Several AC coupled batteries

ian33a — Sat, 13 Jun 2026 05:55:49 +0000

We have a company visiting next week to look at the possibilities of adding a heat pump.

Given the size and fabric of our house, most likely, we will need a beefy sized HP.

A few years ago, when heat pumps were completely off the agenda, we added an AC battery to complement out solar array. The battery needed to be AC because a change to a hybrid inverter would have compromised our generation based FIT. Considering our power needs at the time we went with a 15KWh battery but it only had a 3KWp inverter fitted.

Thinking HP now, the battery may be fine in capacity but it may be compromised on charge and discharge rate if we want to load shift to support a heat pump as well as a reasonable quantity of electrical load in the house.

I very much doubt if it would be possible to swap out the inverter for a larger capacity one (Alpha ESS Smile B3 plus) so, to meet the load demand, I'm wondering if a second AC coupled battery system might be the right approach. The B3 is G100 compliant and I imagine that a second battery would also be. A second battery would also soak up a bit more solar on a good day as we find that our existing battery can get brimmed and, because of our FIT, we don't get anything more for exporting that energy.

Are there any issues with going down that route in terms of legislation or functionality?

thanks

Load Shift and Lifestyle Shift Complete - our journey has ended, for now

AllyFish — Fri, 12 Jun 2026 08:00:24 +0000

Four years ago my wife and I embarked upon our decarbonisation journey. My daughter, then aged 4.5yrs, had subtly changed our mindset about the cost vs return on investment of renewable heating & micro-generation. It was an equation we no longer calculated solely in financial terms, but rather cost vs collective benefit to humanity and her generation. Over time a niggling but increasing moral obligation to do what we could gnawed away at us. *

So we embarked upon removing the old oil boiler and fitting a shiny new 10kW ASHP with £5K BUS grant contribution. We fitted 3.6kW of Solar PV, and we retrospectively added 13kW of BESS. Our heat pump install was done well and the ASHP has been flawless from the get-go, but the commissioning and handover were non-existent. Over the years we've learned through trial and error. We've benefitted from the huge contribution of knowledge this forum has provided - thank you @editor and all. A host of parameter settings needed to be adjusted, and numerous small tweaks made here and there. Over a couple of winter heating seasons we optimised the ASHP CH and DHW control and efficiency and found that elusive weather compensated heating curve sweet spot. If only it could have done it for us out of the box!

We soon realised however that we needed to load shift our electricity import to cheap rates, to allow the ASHP to run continuously for best efficiency while remaining a cost-effective means of heating compared to burning oil. So we added 2x 6.5kW BESS. We work the BESS hard, charging it whenever Cosy has a low rate 3x a day, to leverage the advantage and load shift most of our import to Cosy low rate. (Around 88-90%)

We've recently completed our journey having sold our two jalopy petrol and diesel cars, both with 130K+ miles on them and getting increasingly expensive to keep on the road. The cars owed us nothing. We've gone Chinese - like most things these days - with BYD. A new Dolphin Surf EV and an ex-demo Seal U DM-i PEHV. We've never bought new or nearly new cars before, so this was new territory. Our daily commutes are now all-electric, with the hybrid having a 1300kg towing capacity for our trailer tent family holidays. EV fast chargers on campsites are still anathema in the UK, but on some sites you can cheekily granny charge at 10A load from the electric hook-up.

Both cars are fantastic - we're well impressed with the quality vs value of them. The small EV returns 5miles/kWh, costing 2p a mile on Octopus Cosy cheap rate, less when solar surplus contributes. More Apps on our phones, more head-scratching and yet more settings! We installed a Zappi 7.5kW home charger at home, which is very capable but I didn't find it very intuitive. I've now found the sweet spot where it will timed boost at 7.5kW on the two Cosy cheap overnight rate periods, and granny charge at 1.5kW ECO+ setting at other times drawing from the BESS. Using the BESS that way gives us up to 10hrs of low rate charge overnight in a 'granny-boost-granny-boost' pattern, which no EV tariff offers. We can fully charge the EV overnight that way, but we've never had the battery lower than 45% charge yet on a 200 mile range city EV car used predominantly in a rural environment. One car gets plugged into the Zappi, and if needed one granny charges from an outdoor socket at 2kW. Whichever needs more juice overnight goes on the Zappi. I can charge the PEHV for free at work during the day. What we now save on petrol and diesel per month more than pays for the PCP on the small EV.

* I should add that in the current geopolitical climate where Billionaires send rockets into space for fun, and missiles are fired at anything that moves in the Middle East, our C02 savings seem futile, but we sleep easier knowing we've done our little bit.

Thank you to all who have helped us along this journey. It has been quite a ride!

Daikin ESPAltherma and Home Assistant installation

Bash — Thu, 11 Jun 2026 10:45:14 +0000

I finally have some time to attempt to get ESPAltherma up and running on Home Assistant.

I am quite pleased with myself already that I have managed to get some of this completed. I have started to follow the github process, GitHub - raomin/ESPAltherma: Monitor your Daikin Altherma / ROTEX heat pump with ESP32 · GitHub

I have a lovely old Dell laptop that wasn't upgradeable to W11 and had an ageing battery. It a very low powered (3w when idle with W10 and the screen off), passively cooled, has 8gb of RAM and a 512GB SSD.

So far I have been able to install Home Assistant on the laptop running on ubuntu. The laptop has the black screen with the HA logo in the top left hand corner.

I have installed HA on my desktop computer and integrated the Shelly energy meter which is working perfectly.

I have installed the HA MQTT vis the HA desktop.

I have also purchased and received a (tiny!) M5NanoC6 ESP device which I need to program I assume.

I have downloaded and installed Visual Studio Code and installed PlatformIO IDE core.

This is as far as I have got and am starting to get a little out of my depth in how to complete the setup!

I am a little bamboozled with setting up the M5 ESP device (Getting started - Step 1: Uploading the Firmware).

I am not even sure about step 1 "download the repository folder and open it in Platform IO".

@majordennisbloodnok Would you be able to help me continue down this rabbit hole?!!

As a side note, I'd like to get the laptop screen to timeout as it is constantly on the HA black screen and ideally shut the laptop screen down whilst the HA server continues to run in the background. I am assuming I don't need the screen to be running all the time?!

Thanks.