@ccap as an aside, I think you pose some interesting questions and I will put it before the panel on this week's podcast recording.

@ccap On the subject of TRV’s, when I had the gas boiler and old rads removed, I held on to the Hive PROGRAMMABLE TRV’s I had fitted some years before. I use one of these in our bedroom now as I am able to programme it to any temperature required  for up to, (I think) six different periods a day and all days of the week are controllable separately if wished. The Hive PTRV’s run on 2 x AA cells and I held onto the controller that connects to ethernet and thence via wi-fi to my iPad and the PTRV’s. Regards with apols for a tardy reply, Toodles.

Hi Colin — you’ve clearly thought deeply about the system design, and your questions reflect exactly the kinds of practical challenges that are often left unresolved in theory-driven guidance. So many homes behave in unpredictable ways, you've described — with overlapping heating sources, varying occupancy, and changing comfort needs.

The important thing is this: while appliances and fuels evolve, the hydronic fundamentals behind pressure, temperature, and flow control remain consistent, grounded in thermodynamics, not trends. When those principles are ignored or distorted, systems misbehave, no matter how efficient the equipment is.

Zoning has often been unfairly blamed because it's frequently implemented with outdated or poorly understood layouts. However, when done right — with clear hydraulic separation, accurate return paths, and feedback — the appliance can respond to zoning, providing stability, comfort, and energy savings.

You’re right to question a one-size-fits-all solution. The goal isn’t to sell a system or ideology — it’s to help more people find approaches that work with real homes and real behaviour. No one person or group has all the answers. What matters is a willingness to keep learning — and questioning — together.

Posted by: @harryrea

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Zoning has often been unfairly blamed because it's frequently implemented with outdated or poorly understood layouts. However, when done right — with clear hydraulic separation, accurate return paths, and feedback — the appliance can respond to zoning, providing stability, comfort, and energy savings.

Welcome to the forums, @harryrea. That’s an interesting perspective, and I can see where you’re coming from, but it does run somewhat counter to where many of the best UK installers are heading with their system designs. There’s a definite shift away from zoning and hydraulic separation in favour of simpler, open-loop, unbuffered systems, largely because poorly implemented separation and zoning have consistently led to inefficiencies, short cycling and poor performance.

The issue isn’t necessarily the concept of zoning itself, but rather the practical reality that achieving stable and efficient results in a hydraulically separated, zoned system is beyond the capability of many installers at the moment. So the question I’d put to you is: how do you propose balancing such a system so that it performs on par with a well-designed open-loop setup? What’s your approach to ensuring correct flow rates, minimal return temperature distortion, and appropriate feedback to the heat pump in real-world installations?

Genuinely curious if there’s a proven, repeatable way to do this well.

Posted by: @editor

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The issue isn’t necessarily the concept of zoning itself, but rather the practical reality that achieving stable and efficient results in a hydraulically separated, zoned system is beyond the capability of many installers at the moment.

I'm not sure it's just that tbh.  Many, possibly most, Houses respond slowly particularly if the requirement is to reduce in temperature, and rooms share heat.  So even with.a perfect instal and control system there is a limit to what can be achieved set by the dynamics of the house and the generally poor insulation between rooms.

The question then becomes, is what can actually be achieved (however 'good' the control design) worth the effort.  For me, having tried various controls both with boilers and now my heat pump, the answer is a definite no.  With the house at a more or less constant temperature as a result of the weather compensation, bedrooms a bit lower than living rooms (easily achieved with lockshields), I can go anywhere I want in the house at any time and feel comfortable, whilst paying significantly less than when I was zoning both in time and space with my gas boiler.  Heating problem solved and no need or desire for added complexity and cost.

Of course others will have different needs and so for them zoning properly implemented (provided that the house is capable of responding as the occupant wishes) is likely worthwhile.  But it would wrong to suggest that zoning is some sort of universal panacea or need, or indeed that it is guaranteed to save money.

That said I too am interested in how @harryrea you propose to go about this.  Is it similar to what Adia Thermal are doing for example, or somehow fundamentally different?

You’re absolutely right that many past attempts at zoning and hydraulic separation have failed to deliver the desired results. Poor results, short-cycling, and unnecessary complexity have all left a bad taste, not just for installers, but for homeowners too. The reality is that these systems have often been bolted onto old paradigms or misapplied from commercial practice, and without proper support or training, they've underperformed.

Where I come from, with NRG, it isn’t about promoting zoning as a universal solution — far from it. It's about recognising that when homes do need it (for example, where occupancy or heat source patterns vary), there has been a lack of practical, replicable, and installer-friendly ways to do it right.

My attitude to system design and the NRG approach doesn’t bypass complexity — it just ensures the complexity is placed where it belongs. You can use advanced control strategies if the project demands it, but they’ll be ineffective if the underlying hydronic design is flawed. We focus on getting the fundamentals right first: consistent flow paths, proper pressure zones, predictable return temperatures — the things that enable any appliance, from a basic boiler to a sophisticated inverter-driven heat pump, do its job properly.

These fundamentals aren’t new — correct heat loss, pipe sizing, pump selection, and flow balancing have always mattered. What’s changed is that electricity costs now expose any weakness immediately, especially with heat pumps. Our system structures build in those principles by default, so that a competent installer doesn’t need to reinvent the wheel or learn a whole new language, just apply what should have been best practice all along.

So it’s not about selling a method or a magic box. It’s about making it more likely that an installer can walk away from a job confident that the system will perform as expected, regardless of the controls or appliances used.

I'm always happy to explore specifics if there’s interest, and I welcome the chance to test ideas with people who’ve been on the front line, trying to make these systems work.

Thanks for the input everyone.

It's good to hear some voices supporting the idea of *some* form of zoning if it is designed correctly and the expectations of what can be achieved are reasonable. I'm fully aware of the limitations so if I do implement a limited zone/control system in my installation I know what to expect. And I can always roll back to completely open loop later if it doesn't do what I want it to do. I'd rather spend a little more on the setup now and have options. It may be a good experiment, and perhaps in 18-24 months time I'll be able to report some interesting findings!

Colin

My original “design" from my installer for my 11.2KW heat pump was a 9 zone system.  One of the zones had a flow rate of under a litre a minute.  That zone was in a north facing cold room, and in shoulder season when running on the stats, that one zone would often come on, on its own…….. bonkers.  And this was a reputable installer, whos been interviewed on this channel. I've had 2 low loss headers of some sort, and 5 pumps.  It’s been very tricky to get past the initial design by my installer did, and there have been times where I wanted to rip the heat pump out and go back to gas.  I think I'm now in a place where it’s working better but it’s been a very long and painful journey for both me and my installer.  Even though I'm at the point where I think mine is probably going to be OK now (I'll tell you for sure after one more heating system), some friends have asked about the ASHP and if they should get one, and I have generally tried to put most people off.  But maybe I’ve just had a  bad ride with it.

@davidnolan22 it sounds like you have had a bad time of it. I guess this is why this forum and the various YouTube channels exist, so everyone can learn from past mistakes. Unlucky for you that you had to be one of the guinea pigs!

I'm hoping that I am coming to the ASHP world at the right time to benefit from the lessons that are being learned. But I also am more than aware that today's wisdom may well be tomorrow's cautionary tale so I'm not just taking everything I'm told as gospel!

The biggest mistake in zoning is basing the zones on superficial factors, such as dividing areas by North, South, East, West, or even upstairs and downstairs. Instead, zones should reflect how the space is used or the occupants' lifestyles. For example, consider a family area, a formal or rarely used area, or a bedroom area (if the number of bedrooms warrants it, it may be designated as a guest bedroom zone).

In larger houses, it can be justifiable to have both a main domestic hot water (DHW) cylinder and a typical household cylinder, especially if there is a significant distance between the two areas to prevent unnecessary recirculation of domestic DHW, which is a well-known waste of energy.

While many homes may be satisfied with three or four zones, having too many can lead to frustration. Often, these additional zones are neglected and left on continuously. Another common misconception is that zones are only for shutting off areas when heat is unnecessary, which is inaccurate. Instead, zones are ideal for balancing a system, particularly when using independent pumps. They consume less power than a single large pump running at maximum capacity to meet the demands of the entire system. Moreover, the best practice for operating the system is to keep it running most of the time. Zones will help distribute heat more accurately to match varying heat loads, making setting specific temperature differences (∆Ts) in different areas easier. This directly impacts the performance of the heating appliances, especially heat pumps. Installers often find that if a circulator is correctly installed in a well-designed system, it will function reliably for many years, typically for its entire lifespan.

When a system is designed correctly and the zones are based on how it will operate, homeowners can achieve what they initially desired: control over where and when they want heating and easily adjust the temperature to their comfort in the areas they use. If a single-zone system can achieve comfortable temperatures while preventing overshoot—which is a significant source of energy waste—then utilizing zones will likely lead to further improvements. At the very least, zones can help reduce temperature overshoot and prevent the unnecessary heating of metal distribution components, much like keeping cooking pots warm in case they are needed later.

One last point: If necessary, all of the zones in a system can operate continuously if the conditions warrant it, but for the vast majority of the year, the zones can operate within the appliance's modulation range without a problem.

Posted by: @harryrea

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At the very least, zones can help reduce temperature overshoot

When you say temperature overshoot are you referring to overshoot caused by external factors such as solar gain or cooking, or something else?

Posted by: @harryrea

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While many homes may be satisfied with three or four zones

 An you clarify 'many'.  The vast majority of the UK housing stock is quite modest in size, 60-100 sq m.  Are you suggesting a typical house of this size needs 4 zones or are you referring to much larger houses which are not typical?

Posted by: @davidnolan22

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My original “design" from my installer for my 11.2KW heat pump was a 9 zone system. 

I am really sorry to hear this. I don't know how big your house is but, for comparison and to show that this is not inevitable (and also after learning a lot from this forum) my 200sq m house with a 7kW heat pump has one zone and no llh/buffer etc.  It just worked efficiently from day 1, and I am very grateful to those on here who helped me distinguish the BS from the sensible advice and thus direct or select installers accordingly. 

I do have two rooms with quasi-independent* temperature control  for very specific reasons (so I suppose you might describe it as 3 zones) but otherwise it's essentially an open system on pure weather compensation.  

With 20/20 hindsight I think the key success factors were:

1 right sizing of the heat pump, it was sized based on measured consumption not GIGO spreadsheets

2 simple system and in particular no system separation

3 tuning the WC parameters post install to the minimum flow temperature possible

4 trusting the logic of operating 24*7

Of course there are cases where added complexity can add value, but I think one should always bear in mind that those promoting the add ons are (almost certainly) doing so primarily to make money.  Thus a healthy level of scepticism may be advisable.

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*quasi independent because both are connected thermally to other rooms, because I tend to leave doors open and the partition walls are not insulated, so the degree of actual control is limited.