Homeowners · For new Zealand homeowners comparing water heating delivery systems
Continuous flow or a hot water cylinder: which should you choose?
Choose continuous flow or a cylinder by comparing peak demand, available space, existing services and the installation changes each option needs. Continuous flow heats water as it passes through the appliance, while a cylinder stores heated water for use. Neither arrangement is automatically better, and neither can compensate for unsuitable sizing or distribution pipework.
Checked against official sources on by Stately Plumbing.
The short answer
- Compare continuous delivery capacity with stored capacity and recovery, not just appliance size.
- Keep fuel choice separate from the storage versus continuous flow decision.
- Ask how the proposed system will serve simultaneous outlets and fit the property's layout.
Understand what changes at the tap
A cylinder holds a supply of heated water and replenishes it as the system recovers. Continuous flow heats water during use rather than relying on the same stored reserve. BRANZ treats storage method, energy source, delivery rate and recovery as connected design decisions. The practical question is how the chosen arrangement responds when your household wants hot water, not whether one type sounds more modern or appears smaller in a photograph.
When considering continuous flow hot water, ask what the selected appliance can deliver under the conditions expected at your property. For a cylinder, ask how stored capacity and reheating match the household's pattern. In both cases, discuss the fixtures and existing pipework. A recommendation should connect those details to the proposed equipment rather than relying on a generic statement about unlimited showers or a tank being large enough.
Compare the delivery arrangements directly
The table separates the main questions without declaring a universal winner. A stored system can be well suited to a household's concentrated demand, while continuous flow can suit a different use pattern or space constraint. BRANZ says designers should consider both actual and potential users, fixtures, delivery and recovery. Ask for an explanation grounded in those factors rather than choosing solely on the visible size of the appliance.
Also check what the installer means by each option. A cylinder may use conventional electric heating, a heat pump or another heat source. Continuous flow may use gas or electricity, although the proposal must be suitable for the available services. Comparing a gas continuous flow unit with an electric cylinder therefore changes both fuel and delivery method. Keep those decisions visible so the reasons for the recommendation remain clear.
| Question | Continuous flow | Hot water cylinder |
|---|---|---|
| How is water provided? | Heated as it passes through the appliance | Drawn from a heated store |
| What needs sizing? | Delivery under expected operating conditions | Stored capacity and recovery for the demand pattern |
| What about overlapping showers? | Check total simultaneous delivery requirements | Check available stored water and the wider distribution system |
| What space is needed? | Assess the chosen appliance location and service access | Assess cylinder dimensions, connections and service access |
| What affects waiting at a tap? | Appliance behaviour and the pipe run to the outlet | The stored supply arrangement and the pipe run to the outlet |
| What should a quote cover? | Equipment, services, controls, connections and applicable certification | Equipment, controls, connections, removal and included trade work |
Test the proposal against overlapping use
Describe a realistic busy period rather than an average day. Tell the contractor whether showers overlap, baths are filled, visitors stay regularly or the laundry runs while bathrooms are in use. Mention planned extra fixtures as well as current ones. This gives the designer a better basis for comparing delivery and storage than a simple headcount, which can miss how differently households use the same number of bathrooms.
For hot water cylinders, ask how the proposed storage and recovery would handle that period and what happens after substantial use. For continuous flow, ask how the appliance responds to simultaneous demand and changes in incoming water temperature. Request product specific reasoning, not a promise that any continuous flow unit cannot run short or that any cylinder inevitably will. The selected equipment and the installation determine the practical result.
Distinguish appliance space from whole system layout
Removing a cylinder may release useful indoor space, but that benefit should be assessed alongside the new appliance location and pipe routes. Ask what happens to the old cupboard, connections and any redundant equipment. A proposal to move water heating outside should explain the complete installation, not merely show where a wall mounted appliance could fit. Include service access and any associated building work in the discussion before approving the layout.
Do not assume continuous flow means instant hot water at every tap. Water still travels between the heating source and the outlet. BRANZ recommends short pipe runs to improve efficiency and reduce waste, regardless of the heating arrangement. If waiting time is a main complaint, show the contractor which outlets are affected. Moving the source or changing technology without considering those routes may leave the underlying problem unresolved.
Keep energy choice and running assumptions separate
A storage system is not synonymous with conventional electric resistance heating. Include heat pump water heating if it suits the property and your objectives. Likewise, do not assume every continuous flow proposal uses the same fuel or has the same service requirements. Ask the contractor to identify exactly which energy source and technology are being compared, and explain how the proposed change affects existing electricity or gas arrangements.
Compare ongoing costs using current plans, actual household demand and stated performance assumptions. For a gas hot water option, include the relevant natural gas or LPG supply arrangement rather than a generic fuel claim. For storage, ask how the proposed heating method and controls relate to your use. Neither the absence of a tank nor the presence of insulation is enough to establish the total operating cost of a household system.
When to call a licensed plumber about delivery choices
Both arrangements need appropriate safe delivery temperatures. MBIE says the maximum is 50°C for new personal hygiene fixtures in most buildings installed on or after 2 November 2024 when using the G12/AS1 compliance pathway. The change is not retrospective. Ask the plumber which fixtures and alterations fall within the proposed work. Do not turn a comparison between systems into a reason to adjust thermostats, bypass controls or assume storage and delivery temperatures are interchangeable.
Check the tradesperson's current licence for the work being undertaken, as PGDB recommends. Gas installation or alteration needs appropriately licensed gasfitting expertise, and WorkSafe sets out the associated certification requirements. Ask who is responsible for plumbing, gasfitting and any electrical work, and what handover records are included. Professional responsibilities should be clear before approval, particularly when a conversion involves several trades rather than a straightforward replacement.
Select a complete proposal rather than a product
Ask for written options covering equipment, location, controls, connections, removal and all included trades. Identify assumptions about existing pipework and services, along with any work excluded from the price. If an option changes pressure or requires a new energy supply arrangement, have that shown separately. A complete proposal makes it easier to see whether the quoted improvement comes from the delivery method, the fuel change or repairs to an existing limitation.
If replacing an ageing cylinder is the starting point, the cylinder replacement guide explains the broader process and practical considerations. Use that alongside a site assessment rather than assuming conversion is always preferable. Call a licensed plumber for leaking equipment, unreliable delivery or uncertainty about system condition, and involve a licensed gasfitter for gas related work. The best choice is the arrangement that meets your priorities with its limitations and installation obligations understood.
Common questions
Does continuous flow provide unlimited hot water?
It does not rely on the same stored reserve as a cylinder, but its delivery capacity is still limited by the selected appliance and installation. Ask how it will handle simultaneous outlets under the conditions expected at your home.
Will continuous flow remove the wait at a distant tap?
Not automatically. The pipe route between the heating source and outlet still matters. Ask the installer to assess the affected outlet and proposed layout rather than assuming a change in heating method will remove the delay.
Can a cylinder suit a household with heavy hot water use?
Yes, if the stored capacity, recovery and distribution suit the demand. Ask for the proposal to be assessed against realistic overlapping use and future plans rather than choosing by household size alone.
Does choosing a cylinder rule out more efficient heating technology?
No. A cylinder can form part of a heat pump water heating system rather than relying on conventional electric resistance heating. Ask which storage technologies suit the site and compare them as distinct options.
Who should assess a conversion before I buy equipment?
Start with a licensed plumber who can assess the complete water heating arrangement. Involve an appropriately licensed gasfitter where gas is proposed, and confirm responsibility for electrical work before approving equipment or installation.
Sources
We checked this guide against these official pages. Rules change, so confirm anything that affects a decision with the source.
Need a hand with this?
Stately Plumbing is Kiwi-owned and has worked across Auckland since 2012. Phone us or send the details and we will tell you what we see and give a clear quote before work starts.