@jamespa

Whether zoning is needed depends on how the occupants use the space, the layout of the house, and how heat losses vary between areas. It’s not about the size of the house alone, it’s about diversity of use and performance across rooms.

For example, it doesn’t make sense to put a well-insulated timber-floored living area on the same circuit as a cold, uninsulated stone-walled room and expect one flow rate to suit both. That’s when balancing becomes almost impossible—one circuit needs high flow to deliver heat, and others are oversupplied, leading to energy waste and discomfort.

In systems where a single pump serves multiple zones, that pump usually has to be sized for the worst-case (index) circuit. The other zones then draw what they can from that higher flow rate, which isn’t efficient and undermines control.

Some jurisdictions are already requiring zoning in new builds and deep retrofits, and more are following suit. Personally, I think it should be case by case. A well-designed single-zone system can work brilliantly in some homes. But in others—especially where usage varies, or building fabric is inconsistent—zoning can reduce running costs and improve comfort.

So, I wouldn’t say all homes should be zoned or that none should. But I’d strongly argue that ruling it out entirely, especially in heat pump systems, is premature. Every property and every household is different — and the system design should reflect that.

As for overshooting, I meant primarily system-induced, where an area continues heating because of high ∆T or long cycling, not just from cooking or solar gain (though those matter too). It’s often a symptom of poor modulation, flow mismatch, or oversized emitters running without proper zoning or control.

Posted by: @harryrea

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Some jurisdictions are already requiring zoning in new builds and deep retrofits, and more are following suit. Personally, I think it should be case by case. A well-designed single-zone system can work brilliantly in some homes. But in others—especially where usage varies, or building fabric is inconsistent—zoning can reduce running costs and improve comfort.

The guidance associated with the UK building regs require separate control of each room unless it is not efficient so to do.  

Posted by: @harryrea

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In systems where a single pump serves multiple zones, that pump usually has to be sized for the worst-case (index) circuit. The other zones then draw what they can from that higher flow rate, which isn’t efficient and undermines control.

Please explain why a higher flow rate is inefficient and undermines control.

Posted by: @harryrea

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As for overshooting, I meant primarily system-induced, where an area continues heating because of high ∆T or long cycling

Ok so how does zoning fix that assuming that the radiators or emitter circuits are balanced roughly on the lsvs or fixed loop valves.

Perhaps to clear this up you need to explain exactly what you mean by zoning in the case of a radiator based system and a ufh based system.  We may be talking at cross purposes.  In particular does a zone in your terminology need active control or do you still consider something with passive control a 'zone' (in which case each individual radiator is a zone because the passive control of an lsv will alter it's output and similarly each loop in a ufh is a zone provided it has at least a passive flow control valve in it so it can be balanced)

Posted by: @harryrea

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So, I wouldn’t say all homes should be zoned or that none should. But I’d strongly argue that ruling it out entirely, especially in heat pump systems, is premature.

I agree with that as I say above, although i also would comment that the reason for (actively controlled) zoning needs to be thought through and validated  by asking the questions: is it for comfort or cost and in either case can what is wanted/claimed actually be achieved?

The heating controls industry, at least in the UK, has encouraged us to believe that micro zoning in time and space will save money and increase comfort.  So far the evidence to support this is sparse to non existent, but of course it is in their financial interest.  Since there are some good thermodynamic arguments to the contrary, certainly with heat pumps, the general claims need to be regarded with due scepticism imho. 

For the avoidance of doubt this does not mean that I believe that suitably intelligent control can't work, in fact I believe it can.  However the key is suitably intelligent.  Unless a manufacturer of controls can explain in simple terms how their system is optimised specifically for an ashp (or alternatively guarantee a level of performance or cost saving) I wouldn't personally be prepared to spend money on it, simply because there are too many out there making unproven claims.  Others may of course have more faith in the heating industry.

James,

Your questions cut right to the core of why these discussions matter.

One thing I’ve noticed over the years — and this thread really highlights it — is that we often use the same terms to mean slightly different things, especially regarding “zones” and “controls.” And it’s not just semantics — it shapes how we design and troubleshoot systems.

In a lot of current practice, zoning is seen mainly as a control-layer function — a way to open or close valves, turn pumps on/off, or modulate flow to match demand. But increasingly, I’m seeing that true system performance hinges less on the control devices themselves, and more on the physical layout and how the system behaves hydronically, particularly in terms of pressure, flow independence, and return temperature behaviour.

So, rather than viewing zoning purely as a matter of room-level control or motorised valves, I’m interested in how zones can be used as structural tools — to segment a system into independently operating hydraulic circuits. That way, each zone isn’t just passively reacting to room temperature but is set up to allow the appliance to operate efficiently and predictably.

It’s not a mainstream approach yet, and it’s not tied to any one product or brand, but I do think there’s space to separate functional control (time/temp logic) from structural control (pressure/flow design) in how we think about heating systems. Otherwise, we risk chasing symptoms—like overshoot or short cycling—with smarter controls when the issue might be baked into the system layout itself.

That might be a slightly different angle than usual, but I think these kinds of conversations are precisely where they belong.

James, On your question:

Posted by: @harryrea

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In systems where a single pump serves multiple zones, that pump usually has to be sized for the worst-case (index) circuit. The other zones then draw what they can from that higher flow rate, which isn’t efficient and undermines control.

 

Please explain why a higher flow rate is inefficient and undermines control.

When a single pump serves multiple zones, that pump usually has to be sized for the worst-case (index) circuit — the one with the highest resistance or largest flow requirement. That means it often delivers a higher flow rate than most other zones need. This creates several issues:

1. Imbalanced flow: Zones with lower resistance end up taking more than their fair share of flow, while longer or higher-resistance circuits may struggle. That makes fine balancing nearly impossible — especially when relying only on TRVs or lockshields — and leads to uneven heating, discomfort, and inefficiency.
2. Return temperature distortion: Oversupplied emitters return water hotter than necessary. That has a direct impact on appliance efficiency:
   • Heat pumps suffer a loss in COP as the return temperature rises.
   • If the return temperature creeps above the threshold, condensing boilers can lose their condensing effect entirely.
3. Control instability: Because the flow isn’t matched to demand, the system tends to overshoot in certain areas, short-cycle, and respond poorly to modulation. You end up with symptoms like poor ∆T control, excessive boiler cycling, and a heat source that constantly hunts for the right output.

In contrast, a multi-pump system (through proper hydraulic separation or dedicated zone pumps) allows each zone to operate independently with the flow it needs. This delivers:

• Better system balance and comfort.
• Lower return temperatures and more stable ∆T.
• Improved appliance performance due to more predictable flow and return conditions.
• Often, lower total electricity usage is achieved by avoiding a single oversized pump running flat out.

To put it in real terms, a recent analysis showed that:

• A single-pump system delivering 0.54 L/s at 93.6 kPa used 50.54 W of electrical power.
• A multi-pump system, with hydraulic separation and smaller, appropriately sized pumps, consumed 42.62 W in total while improving control and comfort.

So this isn’t just about electricity at the pump. It’s about whether the system allows the appliance to operate efficiently and predictably. Even the best boiler or heat pump can’t do that if it’s fed unbalanced flows or unpredictable return temperatures.