Gas to Heat Pump Hot Water: What to Check First

More Auckland households are asking us to take out gas hot water and put in a heat pump cylinder. Sometimes the gas unit has failed and the owner does not want to buy another one. Sometimes the cooktop has already gone to induction, and hot water is the last thing keeping a gas account open. Either way, the question is the same: can this house run on a heat pump, and what has to change to get there?

It is a good upgrade in the right house. It is also a bigger change than a like for like replacement, and most of the surprises come from treating it as a simple swap. This is what we check before anyone commits.

Is a heat pump cheaper to run than gas?

A heat pump cylinder uses roughly a third of the electricity of a standard electric cylinder to heat the same water, because it moves heat from the air rather than making it with an element. How that compares with gas depends on your gas price and how much hot water you use, so we do not quote a single number.

The saving people forget is the fixed charge. Natural gas comes with a daily connection charge whether you use much gas or not, and LPG comes with bottle rental. If hot water is your last gas appliance, removing it can remove that charge too. If you are keeping a gas cooktop or fireplace, the fixed charge stays, and the case rests on running cost alone.

Will I run out of hot water?

This is the biggest change, and it deserves a straight answer. A continuous flow gas heater makes hot water on demand and does not run out. A heat pump heats a stored tank, and once the tank is used it needs time to reheat. It is slower to recover than gas.

So sizing matters more than brand. We look at how many people shower in the morning, whether there is a bath, and whether showers tend to happen all at once or spread out. A household that never ran out on gas can run out on an undersized tank. A correctly sized cylinder behaves much like any mains pressure cylinder, and most families do not notice the difference day to day.

Where does a heat pump cylinder go?

Not always where the gas heater was. There are two main types.

Monoblock (all in one). The tank and heat pump are one unit, and it has to go outside. Full of water it is very heavy, so it needs a solid concrete base, not pavers or a timber deck, plus airflow around the unit and room to service it.
Split system. The tank can sit inside, and a separate outdoor unit sits nearby, joined by refrigerant lines. The maker sets a maximum distance between the two, so the tank cannot go just anywhere.

Every manufacturer also sets clearances around the unit so it can be serviced later, and they differ between brands. We check those against the actual spot before you choose a model, not after it arrives. The outdoor unit makes a sound like an air conditioning unit, so we also look at where bedroom windows and the neighbours are. It produces condensate, which needs somewhere proper to drain.

What happens to the gas line?

It gets made safe. A certifying gasfitter caps off the gas supply at the old hot water point, tests the remaining pipework, and records the work. If hot water was the only gas appliance, you can go further.

Natural gas: contact your gas company early and ask how they handle stopping the supply and closing the account, including whether the meter is removed. The meter belongs to the network, not to you, and their process can take longer than the installation itself.
LPG: return the bottles to the supplier and end the rental. The regulator and pipework can be removed or left capped, depending on what else is on the line.

If you are keeping a gas cooktop or fireplace, only the hot water branch is capped, and everything else carries on as before. Because we are gasfitters as well as plumbers, the cap off and the cylinder installation are done by the same team, in the same visit.

What electrical work does it need?

Most heat pump cylinders need a proper electrical supply at the new location, which a gas heater did not. Some models plug into a standard outlet, and others need a dedicated circuit wired by a registered electrician. We confirm which applies at the site visit, so the electrical side is in the quote from the start rather than an extra on the day.

Common questions

How long does it take to switch from gas to a heat pump?

Longer than a straight cylinder replacement. There is the gas cap off, the new cylinder and valves, new pipework to the new position, the electrical connection and commissioning. On most houses it is a single visit of a day or so, with hot water back once the tank has heated. Where the cylinder goes outside and needs a new concrete pad, it takes two or three visits, because a full heat pump cylinder is heavy and the pad has to be poured and set before the unit goes on it. We give you a timeline at the site visit, based on where the cylinder is going.

Can I keep my gas cooktop and still switch hot water to a heat pump?

Yes. We cap off only the hot water branch and leave the cooktop supply as it is. The line is tested afterwards so you know the remaining installation is sound. The one thing to weigh up is the fixed gas charge, which you keep paying while any gas appliance is connected.

Do heat pump cylinders work in Auckland winters?

Yes. Performance drops as the air gets colder, but Auckland winters are mild compared with the conditions these units are designed for. Most models also have a backup element that helps on the coldest days. Placing the outdoor unit away from damp, shaded corners helps it run efficiently all year.

Is a heat pump cylinder mains pressure?

The models we install are mains pressure, which suits a house coming from continuous flow gas. The shower pressure you are used to stays the same. Every mains pressure cylinder needs the correct valve set and a proper drain for the relief valve, and that is included in the installation.

Should I switch before my gas unit fails?

If your gas unit is working well, there is no rush. The best time to switch is when the old unit is near the end of its life, so you are not paying for a replacement twice. If it is already showing signs of trouble, such as running cold or failing to light, get a quote for both options before it stops completely. That way you are choosing, not scrambling.

We install heat pump hot water and cap off gas across Auckland. See our hot water services and gasfitting services, or call 021 837 775.

Replacing Gas Hot Water With a Heat Pump: What Changes, and What to Check First