Do You Really Need to Pour a Concrete Pad for an Outdoor Hot Water Cylinder?

When you’re investing in a brand-new mains pressure cylinder or a high-efficiency heat pump, the last thing you want to do is throw away hundreds of dollars on unnecessary siteworks.

So, let's break down the rules and how to get your base sorted without blowing the budget.

The Weight Problem: Why the Base Matters

Before we look at pavers vs. poured concrete, we have to look at the sheer physics of what we are dealing with.

A standard 180-litre hot water cylinder doesn’t just weigh 180kg. By the time you factor in the heavy steel tank, the insulated outer casing, the valves, and a full tank of water, you are looking at a total weight of around 230kg to 250kg. If you have a larger family and go for a 300-litre cylinder, you’re looking at close to 380kg pressing down on a footprint not much wider than a couple of rugby balls.

If that base shifts, sinks, or tilts even slightly, it puts massive stress on the copper pipework connecting the cylinder to your home. Over time, that stress causes expensive leaks.

What Do the NZ Building Code Rules Say?

Under the New Zealand Building Code (specifically G12/AS1), there isn't a strict law that says, "Thou shalt only use poured concrete." Instead, the code states that the cylinder must be installed on a stable, level surface capable of supporting the weight, and it must be properly restrained against earthquakes using seismic straps secured to the wall studs.

So, how do the two options stack up against the rules?

Option 1: The Humble Concrete Paver (The Budget-Friendly Pick)

Can you use a paver? Yes, absolutely. In fact, our team at the Hot Water Shop uses high-quality concrete pavers for outdoor relocations all the time.

However—and this is a big however—you can’t just chuck a paver down on top of loose grass or mud and call it a day. If you do, the ground will soften in the winter, the cylinder will tilt, and your plumbing will twist.

If you want to use a paver, the ground must be prepared properly:

• The topsoil must be skimmed away down to solid, compacted clay or dirt.
• A level layer of sand, basecourse, or a quick-setting mortar mix should be laid down.
• A thick, heavy-duty concrete paver (usually 600mm x 600mm or larger) is bedded firmly and checked with a spirit level.

The Verdict: If the ground next to your house is stable and properly leveled, a paver is a completely compliant, safe, and cost-effective solution.

Option 2: The Poured Concrete Pad (The Premium Pick)

Pouring a dedicated concrete pad (often boxed out with timber and filled with a quick-set concrete mix) is the gold standard.

You definitely need to spend the extra money on a poured pad if:

• The ground is sloped or uneven: If the site has a tricky gradient, boxing it out and pouring concrete is the only way to guarantee a perfectly flat, level plinth.
• The area suffers from surface water: If rainwater pools against that side of the house during heavy downpours, pouring a concrete pad allows the plumber to raise the cylinder a few inches off the ground, keeping it safe from moisture and rust.
• You are installing a Heat Pump Cylinder: Heavy-duty, all-in-one heat pump cylinders can be vibratory and incredibly heavy. Manufacturers often explicitly specify a poured concrete pad to anchor the unit securely.

Tim’s Pro Tip: The Alignment Trick

Whether you choose a paver or poured concrete, make sure you position the base so that the cylinder sits right between two of your house's internal wall studs. Why? Because the earthquake straps must be screwed securely into solid timber studs, not just the external cladding. Getting the alignment right now saves a massive headache during installation!

The Final Verdict: Save the Money or Spend It?

You do not need to spend extra money on a custom-poured concrete pad if you already have a flat, stable, well-draining clay or dirt pathway where the ground can easily be prepared to take a heavy-duty concrete paver. A properly laid paver will comfortably pass inspection and keep your cylinder stable for decades.

Save that extra cash for high-quality, weather-proof insulation wrapping—which is highly recommended for keeping your power bills down on outdoor units!

Thinking about moving your hot water system outside? Don't guess the siteworks. Give the team at the Hot Water Shop a call, and we’ll help you figure out the smartest, most cost-effective setup for your home.

‍