There are two moments that usually send Christchurch homeowners looking into this question. The first is standing in a shower that’s gone cold halfway through, again, because someone else in the house used the last of the hot water. The second is opening a power bill that’s crept up and wondering whether your hot water cylinder is quietly costing you more than it should.

Both are good reasons to weigh up continuous flow gas hot water against a traditional cylinder. This guide compares the two honestly, including when a cylinder is still the better choice, so you can make the call that actually suits your household rather than the one that suits whoever’s selling you a system.

How Continuous Flow Gas Hot Water Works

Continuous flow (also called instantaneous) gas hot water doesn’t store any water at all. Cold water passes through the unit, a gas burner heats it on the way past, and hot water comes out the other end as soon as you turn the tap on. There’s no tank sitting there keeping a store of water hot in case you need it.

That’s the whole appeal in a nutshell: you’re only heating water at the moment you use it, and because there’s no tank, there’s no running out partway through a long shower or a busy laundry day.

How A Traditional Hot Water Cylinder Works

A cylinder takes the opposite approach. It heats a full tank of water and keeps it at a set temperature around the clock, topping itself up as hot water is drawn off and cold water flows in to replace it. It’s a familiar, well-proven system, and for a lot of Christchurch homes it still does the job perfectly well.

The trade-off is that the cylinder is heating and reheating water all day, whether you’re home to use it or not, which is where the “pay for what you use” argument for gas hot water comes from.

Key Differences That Actually Matter

Short answer: gas hot water is generally cheaper to run than an ageing standard electric cylinder because it avoids standing heat loss, but a well-insulated cylinder, and especially a heat pump hot water cylinder, narrows that gap considerably. The bigger practical differences for most households come down to space and supply, not just running cost.

Running Costs: Pay For What You Use vs Heat And Store

With gas hot water, you’re not paying to keep a tank of water hot between uses, which is a genuine saving over an older, less efficient cylinder. That said, this isn’t a reason to write off cylinders altogether. A heat pump hot water cylinder can bring running costs down significantly too, without giving up stored capacity. If cost alone is your main driver, it’s worth weighing gas against a heat pump upgrade rather than assuming gas automatically wins.

Upfront Cost: How Gas Compares To Your Cylinder Options

Running costs are only half the picture. The upfront cost of installation varies a fair bit depending on which system you choose, and it’s worth setting them out plainly before deciding. The figures below are indicative, plus GST, and reflect a straightforward conversion or replacement, please confirm current pricing for your specific property with our team.

A low pressure hot water cylinder replacement, reconnected to your existing pipework, is the most affordable option at around $1,800. Moving to an outdoor hot water cylinder, which frees up cupboard space inside the house, runs to roughly $2,800, with a concrete pad an extra $450 if one’s needed. Continuous flow gas hot water, with no storage tank at all and a gas bottle set-up if reticulated gas isn’t available, sits higher again at around $3,800. Heat pump cylinders carry the highest upfront cost of the options here: a Rheem Ambi-power 280E comes in at approximately $4,313.27, while a larger-capacity Rinnai 275L is around $5,266.29.

At a glance, gas continuous flow sits in the middle of the pack for upfront cost, more than a straight cylinder swap, but less than either heat pump option. Where it tends to win back that difference is in the running costs discussed above, since there’s no tank sitting there heating water you’re not using.

It’s also worth noting that a heat pump cylinder costs more upfront than gas but keeps the reassurance of stored capacity, which matters if your household values having a full tank ready to go rather than relying on the gas unit heating water on demand.

Space: Reclaiming Your Cylinder Cupboard

Removing the cylinder frees up whatever cupboard or storage space it was taking up in the house. For smaller homes or older properties where that cupboard is prime storage real estate, this is often the single biggest practical win of switching to gas.

Supply: Never Running Out vs Tank Capacity Limits

If your household regularly runs a cylinder dry, whether that’s back-to-back showers before school or a big family doing laundry and dishes at once, continuous flow gas solves that problem outright. There’s no tank size to outgrow.

Installation: Converting An Existing Setup

Converting from a cylinder to gas continuous flow typically means draining and disconnecting the existing cylinder, altering the pipework to run to an outdoor unit, and, if you don’t already have reticulated gas, setting up an LPG gas bottle supply with copper pipework run to the unit. Water pipework and gas bottle placement both need to sit within set distances of the unit itself, so the practicality of a conversion depends a bit on your property layout. A licensed gasfitter can assess this properly on site.

What Converting To Gas Continuous Flow Involves

Most conversions can be completed in a single day. The general process is:

• Draining and disconnecting the existing hot water cylinder
• Altering the hot and cold water pipework to run to an outdoor gas hot water unit
• Lagging (insulating) the pipework so it performs properly outdoors
• Setting up an LPG gas bottle station and running copper pipework to the unit, if reticulated gas isn’t available at the property
• Testing and commissioning the finished system

If you already have reticulated natural gas at your Christchurch property, the conversion is generally more straightforward again, since there’s no bottle station to set up.

When A Cylinder Still Makes More Sense

Gas continuous flow isn’t automatically the better choice for every home, and it’s worth being upfront about that:

• If you don’t have gas at the property and don’t want ongoing LPG bottle refills, a cylinder avoids that dependency entirely.
• If lowest possible running cost is your main priority, a heat pump hot water cylinder is genuinely worth comparing against gas rather than assuming gas wins by default.
• If your household is smaller or your hot water use is modest, the “never running out” advantage of gas matters less, and the standing cost gap between gas and a well-specified cylinder narrows.

The honest answer is that both are good systems. Which one is right depends on your gas access, your household’s hot water demand, and what you’re actually trying to solve, whether that’s space, supply, or running cost.

Christchurch-Specific Considerations

Reticulated natural gas is available across parts of Christchurch, though not everywhere, so one of the first things worth checking is whether your property already has a gas connection or would need an LPG bottle set-up instead. Either way, this is a job for a licensed gasfitter, since gas installations in New Zealand need to meet compliance and safety requirements regardless of which fuel source you’re using.

Frequently Asked Questions

Is continuous flow gas hot water cheaper to run than a cylinder? Generally yes compared with an older standard electric cylinder, since there’s no standing heat loss from stored water. The gap narrows considerably against a heat pump hot water cylinder, so it’s worth comparing both before deciding based on running cost alone.

Can any home convert from a cylinder to gas continuous flow? Most homes can, but the practicality depends on whether you already have a reticulated gas connection or need an LPG bottle set-up, and on how far the water pipework and gas bottle station would need to run from the unit. A site assessment from a licensed gasfitter will confirm this for your property.

How long does the conversion take? A standard conversion from cylinder to continuous flow gas hot water typically takes less than a day.

Do I need a gas connection already, or can LPG bottles be used? Either works. If reticulated natural gas isn’t available at your property, an LPG gas bottle station can be supplied and installed as part of the conversion.

How does the price of gas hot water compare to a cylinder? As a general guide, continuous flow gas hot water sits above a straightforward cylinder swap but below a heat pump cylinder upgrade in upfront cost. A low pressure cylinder replacement is the cheapest option, gas continuous flow sits in the middle, and heat pump cylinders carry the highest upfront cost while typically offering the lowest running costs over time. Exact pricing depends on your property, so it’s best confirmed with a site assessment.

Talk To Whitehead Plumbing & Gas About Your Options

Whether you’re leaning towards continuous flow gas hot water or want to weigh it up against a cylinder replacement or upgrade, our licensed gasfitters and plumbers can talk you through what will actually work for your Christchurch home. Get in touch or call 03 379 0711 to book an assessment.