Underfloor Heating for a Central Otago New Build — and How Cooling Fits In

Central Otago is one of the most beautiful places in the country to build a home, and one of the most demanding to heat. Alexandra, Cromwell, Queenstown, the Maniototo — these are places that drop to -10°C and below on a winter night, sit under frost for the better part of seven months, then turn around and deliver hot, dry summers. A house here has to handle both ends of that range.

We focus on Central Otago in this article because its extremes make the trade-offs sharp and easy to see. But the same thinking applies right across the region — hydronic underfloor heating is a strong option in any new build through Otago and Southland wherever there's a concrete slab. Central just throws the differences into the clearest relief.

The question we hear most from new-build clients is some version of "underfloor heating, or heat pumps?" — and it's the wrong question, because it treats them as rivals. They're not. They're two different ways of moving warmth (and coolth) around a home, each brilliant at one job and ordinary at the other. Understand that, and the answer usually stops being either/or and becomes the right tool for each job.

One thing worth saying before the detail. When you're building, the budget gets pulled in every direction you can see — joinery, glazing, tapware, the finishes you point to on a walk-through. Heating is the thing you can't see, so it's often first to be trimmed. But it's what decides how the finished home actually feels to live in: your family's warmth, comfort and wellbeing through a long southern winter. A beautiful home you're cold in isn't really finished.

The short version: Underfloor gives you the best heating there is — even, invisible, radiant warmth — while a discreet system handles summer cooling. The trick is using each for what it does best.

At a glance:

• The comfort you never see and never stop feeling — warm floors, nothing on the walls
• Radiant heat for heating, a convected system (ducted or heat pumps) for cooling: best of both
• Ideal for polished concrete, vaulted ceilings and big glass — where wall units struggle
• Cleaner air, with no blown dust or allergens
• The same heat pump can heat your domestic hot water too
• Has to be designed in before the slab is poured — get us in at the design stage

Radiant or convected: the distinction that explains everything

There are really only two ways to change the temperature of a room.

The first is radiant: you warm the surfaces and objects in the space — the floor, the walls, the furniture, the people — and they in turn keep you comfortable. Underfloor heating is radiant. The floor itself becomes a gentle, low-temperature heater, and the warmth radiates up and out evenly across the whole room.

The second is convected: you heat (or cool) the air and move it around. A wall heat pump, a ducted system, a fan coil — these all condition air and blow it through the space.

Here's the thing that matters for a Central Otago build: radiant is the better way to heat, and moving air is the better way to cool. Radiant heat feels even and draught-free, with no hot blast and no cold corners, and it does it without stirring the air. Cooling, on the other hand, essentially has to involve conditioning and moving air. So the ideal home doesn't pick one technology — it uses radiant warmth for heating and a convected system for cooling, and gets the best of both.

What hydronic underfloor heating is, and why it suits new builds here

Hydronic underfloor heating — sometimes called water-fed underfloor — runs warm water through a network of pipes embedded in your floor slab. An air-to-water heat pump heats that water, and the warmth radiates gently up through the floor. The room heats from the ground up: the floor is warm underfoot, the warmth is even, draught-free, and quietly everywhere.

And the direction of travel is clear. As the cost of running fossil-fuel boilers keeps climbing, air-source hydronic heat pumps have become the obvious way to drive a system like this. They run on electricity — and with around 80 to 90% of New Zealand's electricity coming from renewable sources, an efficient heat pump isn't just cheaper to run than a diesel or gas boiler, it's a much cleaner way to heat. (If you're replacing an existing boiler, Replacing your boiler with a heat pump goes into this in detail.) There's a bonus, too: the same air-to-water heat pump that warms your floors can heat your domestic hot water off the one system, efficiently — so you get more from the investment (see Heat pump hot water).

Because underfloor is radiant rather than blown, it brings a set of benefits that air-based heating simply can't match:

• It's kinder to the air you breathe. It doesn't blow air around, so it doesn't stir up dust or allergens the way a forced-air system does. The result is a cleaner, more even environment — research has measured noticeably lower airborne particle movement with underfloor heating than with forced air — which is genuinely worth something to anyone in the house with hay fever, asthma or allergies.
• It's invisible. No wall units, no radiators, nothing on show. That's a gift in a contemporary architectural home: vaulted ceilings, big runs of glass and open-plan spaces — the very things that defeat a wall-mounted heat pump — are all heated quietly from the floor, with nothing to interrupt the design.
• It's made for a polished concrete floor. If you're pouring a polished slab as your finished floor, underfloor is the obvious choice: the slab is both the surface you walk on and the thing doing the heating.
• It's comfortable and quiet. Even warmth, no draughts, no fan noise, and a gentle effect on indoor humidity rather than the drying you get from blown air.

This is also where we earn our keep, and it's why we always want to be at the table at the design stage, alongside your architect — not brought in once the plans are locked. Early involvement lets us do three things properly: work out where the equipment can sensibly live; understand exactly what we're heating and how much, room by room; and read the thermal properties of the home — its insulation, glazing and orientation — so we can design the system bespoke to that house. Underfloor done off a rule of thumb disappoints. Underfloor designed properly for the home it's in is superb.

The limitations, because they're real

Underfloor isn't magic, and we'd never pretend otherwise. It's slow: the thermal mass of the slab that gives you such steady warmth also means you can't turn it up when you feel cold — it takes hours to bring a slab from cold to comfortable, so it's designed to run continuously or on a gentle setback rather than flicked on and off. It heats only (more on the cooling question in a moment). And it's a more significant investment than wall units. Done properly it's worth it — but the budget has to be there for it.

Cooling: the convected half of the equation

Central Otago summers are genuinely hot — 30°C afternoons in Alexandra are not unusual — so cooling matters here, and underfloor can't really do that job on its own. This is where a convected system comes in.

Where there's space for it, the most elegant way to add cooling is a ducted system: discreet, whole-home, with nothing on the walls — which keeps exactly the clean architectural look that drew you to underfloor in the first place. We can reverse-cycle the heat pumps to run cooling through fan coils, including ducted fan-coil units, to cool the home. Where ducting isn't practical, high-wall or floor-mounted heat pumps are a perfectly good, independent way to add cooling.

There's one honest pitfall worth naming here, because we see it happen. A ducted system can both heat (by blowing warm air) and cool — so when a budget tightens late in a build, there's a temptation to drop the underfloor and "let the ducted do both." You can do that, and it will work. But you'd be trading away the very thing that makes a well-heated home feel special: that even, radiant warmth underfoot, with nothing on show. Our advice is to protect the underfloor for heating and let a convected system do what it does best — cooling — rather than collapsing both jobs onto the system that does neither quite as well. Underfloor for warmth, discreet ducted for cooling, is the cleanest result there is.

Slab cooling: the quiet trick most people don't know about

There's one more option worth knowing, because it surprises people. The same hydronic slab that heats your home in winter can do a little cooling in summer. Put the heat pump into reverse cycle and you can gently chill the slab.

A few things to understand about it. The effect is subtle — chilling the slab will take perhaps 4 to 6°C off the indoor temperature, a gentle take-the-edge-off rather than the blast of an air conditioner. It's also strictly seasonal: you switch it on for the heat of mid-summer and leave it running, because with all that thermal mass you really don't want to be lifting the slab's temperature to heat and then dropping it to cool and then lifting it again — that's slow and hugely inefficient. Slab cooling is a "set it for the season" thing, not a 24-hour on-off one.

The crucial part — and this is non-negotiable — is control. A slab-cooling system has to monitor humidity and dew point so it never chills the floor below the temperature at which condensation forms. Get that right and it's a lovely, subtle effect; get it wrong and you'd have water forming on a cold floor and condensation problems through the house. It can absolutely be done, but it has to be set up properly and, above all, controlled properly — which is exactly the kind of thing we design in from the start rather than bolt on later.

The one thing we won't compromise on: sizing

In Central Otago more than anywhere else in our territory, an undersized system is a real and common problem. The design temperatures here — typically -10°C to -15°C — are a long way colder than the coastal parts of the region, and a system sized to a softer standard will simply run out of puff on the worst days. So we do proper load calculations, every time. We don't size by gut feel or rule of thumb. The heat a building loses at its design temperature is a calculable number, and that number is what drives the specification. Get it wrong and you've built a beautiful home that can't keep itself warm in July.

Have this conversation before your slab goes down

If you're in the design stage of a new build anywhere in Otago or Southland, now is the moment. Once the slab is poured, your underfloor options narrow sharply, so the time to weigh all this up is while there's still flexibility to act on it. We're happy to work alongside your builder and architect at design stage to make sure the right combination — radiant warmth for heating, a convected system for cooling — is planned in from the ground up.

Building in the region? Get in touch early and we'll help you get the heating and cooling right from the start.

Frequently asked questions

Is underfloor heating worth it in Central Otago?
For many new builds, yes. It delivers even, draught-free radiant warmth that suits the long, cold winters in Alexandra, Cromwell, Queenstown and the Maniototo — and because it doesn't blow air around, it's cleaner and kinder for anyone with allergies or asthma. It's invisible, ideal under a polished concrete floor, and pairs efficiently with an air-source heat pump. The main trade-offs are a higher upfront cost and a slow response, so it's designed to run steadily rather than on and off.

Can I add underfloor heating after the slab is poured?
It's far better — and far cheaper — to do it before the pour, which is why this is a design-stage decision. It isn't strictly impossible afterwards: there are lightweight overlay systems that sit on top of an existing slab (though they raise the floor level, so doors and joinery need lifting by around 45mm), and pipes can even be cut into channels in the concrete. But that's expensive and time-consuming, so it's very much a last resort.

Does underfloor heating cool the house in summer?
Its main job is heating, but the same hydronic slab can be reverse-cycled to gently chill the slab in summer — a subtle effect that takes around 4 to 6°C off the indoor temperature, not the blast of air conditioning. It has to be controlled with humidity and dew-point monitoring to avoid condensation, and it's run seasonally rather than on and off. For stronger cooling, you'd pair the underfloor with a ducted system or a couple of well-placed heat pumps — which is exactly why the combination of underfloor for heating and heat pumps for cooling works so well in Central Otago.

Warm and Cool are HVAC specialists based in Dunedin, serving Otago and Southland. We design, supply, and install heating, cooling, and ventilation systems for homes and commercial buildings throughout the lower South Island. We regularly work with builders and designers in Queenstown, Wanaka, Alexandra, Cromwell, and surrounding areas.