Installing and Changing Over Hot Water Units

The straightforward version

If your existing unit is in a sensible position, the same fuel type is going back in, and the connections line up, a replacement is a short job. Isolate the power or gas, shut the water, drain the cylinder, break the connections, remove the old unit, set the new one, reconnect, refill, purge the air, check for leaks, relight or re-energise, and test.

Two to three hours is normal. The variable that catches people out is drain time: a full 250 or 315 litre cylinder takes a while to empty, particularly if the drain point is at the back of a narrow side passage.

What turns a half day into a full day

A fuel changeover. Going from electric to gas needs a gas point run to the unit, which is licensed gas fitting work, and the redundant electrical circuit dealt with. Going from gas to heat pump needs a suitable power circuit and enough clear air around the unit to breathe.

A relocation. New water lines, often a new gas run, sometimes a new base or wall bracket. The upside is real — see the note on positioning below.

A base or bracket problem. Old steel stands rust out from the bottom. A cylinder sitting on a failed stand or a cracked pad needs that fixed first, and no installer should set a new tank on a base that will not hold it.

Compliance catch-up. A tempering valve where the old unit had none. A relief valve drain line that discharges somewhere it should not. An unsafe flue termination on a gas unit. These come up regularly on units installed decades ago.

Positioning is the free upgrade

Where the unit sits affects how long it lasts and how well it performs. Three things are worth getting right.

Distance to the fixtures. Every metre of pipe between the heater and the shower is a dead leg you run to waste each morning. On a long-and-narrow Perth block with the laundry at one end and the ensuite at the other, moving the unit closer to the wet areas is measurable in both water and patience.

Exposure. A unit on a west-facing wall takes the full afternoon sun and the salt-laden sea breeze that comes in most summer afternoons. On coastal suburbs — Scarborough, Fremantle, Rockingham — that exposure shortens casing and bracket life noticeably.

Noise. Heat pumps run a compressor and a fan. Against a bedroom wall or a neighbour's boundary, that is a problem you will hear about. Against a laundry wall or a side passage, it is not.

Sizing without the guesswork

For storage, the rule of thumb most installers work to is roughly 50 litres per person per day for gas storage and more for electric on a controlled tariff, because the tank has to carry the household through to the next heating window. For continuous flow, the number that matters is litres per minute at a given temperature rise — a 16 L/min unit will not comfortably run two showers and a kitchen tap at once, a 26 L/min unit will.

Undersizing is the most common regret. Oversizing costs money you did not need to spend and, on storage, wastes standing heat every day.

After the install

You should be left with the appliance manual, the warranty paperwork, and a compliance notice for the work performed. Keep them. Warranty claims on cylinders routinely turn on being able to show the unit was installed correctly and when.

If the system develops a fault later, the repairs page covers what to check first. If the old unit fails before you have planned anything, emergency replacement is the faster path. Pricing ranges are set out in the cost guide.