Replacing Your Boiler? Your Heat Pump Options in Southland and Otago

If you've got central heating running off a boiler — diesel, wood, coal, wood pellet or an electric element — you'll know the signs when one starts to tire. The repairs come more often. A part takes weeks to source. Most boilers will give you somewhere between 15 and 25 years, so at some point the question of what to do next comes up.

But here's what's changed, and it's worth pausing on. These days the trigger to replace a boiler often isn't age at all — it's running cost. We've swapped out boilers that were nearly new, simply because the spiralling price of diesel and gas had made them painfully expensive to feed. The boiler still works fine; it's just costing a small fortune to run.

A quick word on gas, because it catches people out. Very few places in New Zealand have reticulated (piped) gas, and there's no reticulated natural gas anywhere in the South Island at all. Within our region, only parts of Queenstown and Wanaka have a piped LPG network — everywhere else, Dunedin, Invercargill, Gore and across Central, runs on bottled LPG. A 45kg bottle costs somewhere around $170–$180 and doesn't last long feeding central heating, which is a big part of why gas-fired central heating gets expensive so fast. Diesel, coal, pellets and electric-element boilers all tell a similar story: they're all costly to run compared with a modern heat-pump system.

Whatever you're burning, it's worth stopping to look at the whole picture before you commit to another like-for-like replacement — because the alternative has changed enormously.

The short version: Boilers are getting expensive to run — and a modern heat pump now does the same job, on your existing radiators or underfloor, for a fraction of the running cost.

At a glance:

• A warm home you can actually afford to keep warm — that's what a conversion buys you
• Heat pumps run at 200–500% efficiency, against a boiler's 40–80%
• Modern (R290) heat pumps reach 65–75°C, so they suit radiators, not just underfloor
• Works with diesel, gas, coal, wood, wood-pellet or electric boilers
• We do dozens of conversions a year — and set them up to protect your new gear
• We haven't fitted a new boiler in over four years; it's all heat pumps now

Why this isn't the simple swap it used to be

A decade ago, a dead boiler meant another boiler. Today that's rarely the sensible call, for a few reasons.

Heat pump technology has come a long way. Modern air-to-water heat pumps now hold their output in the bitterly cold temperatures Otago and Southland serve up every winter — and, just as importantly, they can now reach much higher water temperatures than they used to. That's the breakthrough that matters here: it means a heat pump is no longer just a partner for low-temperature underfloor heating. It can run a radiator system too, which is what most boiler-heated homes have.

Then there's the sheer efficiency gap. A boiler — whatever it burns — typically runs at somewhere between about 40% and 80% efficiency; you never get back more energy than you put in. A heat pump plays a completely different game. Because it moves heat rather than making it, it effectively delivers anywhere from around 200% to over 500% — two to five times the energy it draws — depending on the make, model, ambient conditions and how it's set up. That's not a typo; it's the whole point of the technology.

And for many homeowners there's a quieter motivation too: a wish to move off fossil fuels. In New Zealand that stacks up, because our electricity comes largely from renewable sources — so a heat pump isn't just cheaper to run, it's a much cleaner way to heat.

What your realistic options look like

We should be upfront about how we work: we haven't installed a new boiler in over four years. We now do these conversions entirely with heat pumps, in homes and commercial buildings alike, because in our experience that's what delivers the best long-term result. Here's what the paths typically look like.

A straight conversion. An air-to-water heat pump replaces the boiler as the heat source while keeping your existing radiators and underfloor circuits. It sits outside like a normal heat pump, but instead of blowing warm air into a room, it heats water that flows through the system you already have. For a lot of homes, this is all that's needed — and the same heat pump can often look after your domestic hot water as well, which stretches the benefit further (see Heat pump hot water in Otago and Southland).

A conversion with some radiator changes. If your radiators are old, undersized or due for replacement anyway, it can make good sense to resize or replace a few of them as part of the job, so the whole system is matched to the heat pump's operating range. It's a bigger job, but it gives you a system built to perform well for twenty-plus years.

Running a heat pump in parallel. Sometimes the smart move is to keep an existing boiler in play alongside a new heat pump. We see this most with wood or coal gasification boilers, where the owner has ready access to firewood and is happy to keep using it. The heat pump goes in as a backup — but it can quietly become the primary source over time, which is ideal for anyone who's finding that chopping and loading wood, or lugging and managing coal, is getting less appealing (or less practical) as the years go on. You keep the option, without being chained to the chore.

The detail that catches people out: flow temperature

This is the one technical point worth understanding, because it's where boiler conversions used to come unstuck — and where the technology has moved fastest.

Boilers run hot. In practice we see them set anywhere between about 50 and 80°C, often lower than people assume. Heat pumps, traditionally, ran cooler — 35 to 55°C — which made them a perfect match for underfloor heating. Running radiators at that lower temperature is perfectly achievable too: it just means the radiators need to be large enough to deliver the heat the room needs at that gentler temperature, and in a well-insulated home, slightly longer run times comfortably make up any difference. And these days you often don't even need to think about it — modern heat pumps using R290 (propane) refrigerant and other newer technology comfortably reach 65 to 75°C and beyond, temperatures that are ideal for radiator central heating. In other words, a heat pump today is a true high-temperature replacement for a boiler, not just an underfloor solution.

Exactly how this plays out depends on your radiators and how quickly your home loses heat — its insulation, glazing and the like — which is one of the things we work out properly rather than guess, and exactly why we won't quote a conversion off a phone call.

What Southland's climate demands

Southland and Central winters are the real thing. Invercargill regularly sits below zero overnight, and frosts run from May right through to September. Whatever you install has to perform reliably in that, not just on a mild day.

That's why we work mainly with Stiebel Eltron and Mitsubishi Electric. Mitsubishi's Zubadan heat pumps are purpose-built for cold-weather performance, and Stiebel Eltron's German-engineered units are designed to hold their output as the temperature drops. Not every air-to-water heat pump is built for cold-climate work — a unit that fades at -5°C is no use to you here — so getting the right one matters.

Questions worth answering before you decide

Before you settle on anything, it's worth getting clear on a few things — and these are exactly what we'll work through with you.

What condition are your radiators actually in? Old cast-iron radiators can be viable for a heat-pump conversion, because their mass means they radiate happily at lower temperatures. How well insulated is the home? A heat pump rewards good insulation, so it's worth knowing where you stand. And are you planning to extend the house? If a renovation will add heat load, it's far better to allow for that from the start than to discover it later — because the fix isn't a simple retrofit, it's sizing the heat source bigger up front, or planning to add a second heat pump down the track. Both cost more if they're an afterthought.

What we've actually seen on the ground

Boiler conversions aren't a sideline for us — we've been doing them for many years, we do dozens every year, and we're very good at them now. We understand what's involved in making a conversion work properly, and just as importantly, in protecting your new equipment so it gives you a long, reliable life. And it's not just diesel and gas: we convert coal, wood, wood pellet and electric boiler systems too.

It's worth saying that plenty of people are quite fond of their boiler, and fair enough — a good diesel or gas boiler does a fine heating job, and indoors it's clean: no smell, no fumes. The problem is simply what it costs to run, and the fact that burning fuel isn't environmentally sound. A heat pump sidesteps both: far cheaper to run, and powered by electricity that in New Zealand comes largely from renewable sources.

For most owners the change is felt inside the first winter — not only in the running costs, but in a home that's warm and affordable to keep that way. That everyday comfort is really what the whole exercise is about.

How we'd approach it with you

When you call us about a boiler, we don't open with a product. We start with a site visit — assess the existing system, measure the home, look at the insulation, and understand how you actually use your heating. Then we lay out the options with honest information about what each one means for performance, comfort and running cost, and we design the right system around your home.

One last practical note: plenty of homeowners fund heating upgrades through low or no-interest loans from their bank, so it's worth a conversation with yours before you assume the better long-term option is out of reach.

Thinking about your boiler? Get in touch for a straight, no-obligation assessment.

Frequently asked questions

Can I replace my boiler with a heat pump in Southland?
In most cases, yes — and these days we do these conversions entirely with heat pumps. An air-to-water heat pump replaces your boiler as the heat source while keeping your existing radiators and underfloor circuits. There are exceptions where it isn't viable, which is exactly the kind of thing we check on a site visit before recommending anything.

Will an air-to-water heat pump work with my existing radiators?
Increasingly, yes — and this has changed a lot recently. Boilers run hot (around 50–80°C), and older heat pumps topped out around 55°C, which suited underfloor better than radiators. Modern heat pumps using R290 refrigerant now reach 65–75°C, making them a genuine high-temperature replacement for a radiator system. Whether your specific radiators suit comes down to their sizing and your home's heat loss — sometimes running a little longer at a lower temperature compensates — and we assess that properly before quoting.

Do heat pumps actually work in Invercargill's cold winters?
The right ones do. We specify cold-climate units built for the job — Mitsubishi's Zubadan range and Stiebel Eltron's German-engineered units both hold their output at low temperatures. A unit that fades at -5°C is no use here.

Is a heat pump cheaper to run than a gas, diesel, coal or wood boiler?
For most homes, yes. An air-to-water heat pump delivers two-and-a-half to four units of heat for every unit of electricity it uses, so running costs typically come in well under diesel, LPG or coal — and there's no fuel to order, store or handle. The exact saving depends on your electricity tariff and how the system is run, and we'll give you a realistic picture for your home rather than a best-case brochure number.

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.