Boiling Water Tap vs Kettle: We Ran the Numbers

If you're considering a boiling water tap for your kitchen, you've probably already thought "They cost a fortune to run because they're heating water 24 hours a day."

It sounds reasonable. A tank of water held at near-boiling temperature around the clock has to be expensive right?

We weren't sure either. So we tested it.

How We Tested

We set up a side-by-side comparison between our 2-in-1 boiling and filtered tap (2.4L tank, holding water at 98°C) and a standard 2100W kettle. Both delivered the same daily output: ten cups of near-boiling water at 250ml per cup, spread across a 24-hour period.

Ten cups a day is a reasonable estimate for a typical New Zealand household, a couple of teas in the morning, coffee through the day and hot water for cooking.

For the kettle, we tested two scenarios:

• Filled to 1 litre per boil

• Filled to 1.5 litres per boil

We measured total power consumption over 24 hours and costed it at 30c per kWh, which is around the NZ residential average.(Q1 2026)

The Results

The boiling tap costs about 20 cents per day, roughly $6 a month.

That's $1.40 more than someone who carefully fills their kettle to exactly what they need, and 50 cents less than someone filling to 1.5 litres.

Why the Tap Isn't Much More Expensive

The idea that a 24/7 hot tank must cost a fortune is wrong, and here's why.

A boiling tap doesn't run at full power continuously. It heats the tank to 98°C, then cycles off. 

The element only fires again when:

1. Water is dispensed (replaced by cold mains water that needs reheating)

2. The tank cools below its setpoint and needs a small top-up

The standby cost,  keeping the tank warm between uses,  is genuinely small, because the tank is insulated and loses heat slowly.

The kettle isn’t very well insulated and usually starts from cold mains water every time. That means it pays the full cost of heating water from ~15°C to 100°C, even if you only end up using a fraction of what's in there.

The maths in plain terms: heating one litre of water from 15°C to 100°C takes about 0.1 kWh. If you fill the kettle to 1.5L but only pour out 250ml, you've paid to heat 1.5 litres and used one-sixth of it. The rest cools down on the bench until you reboil it later.

That's why the 1.5L kettle costs more than the boiling tap, despite the tap running 24/7.

What the Numbers Don't Show

Running cost isn't the only factor that matters, and arguably it's not even the main one.

Time. A kettle takes 60–90 seconds to boil. A boiling tap delivers near-boiling water in a few seconds. If you make six hot drinks a day, that's roughly five minutes of waiting saved daily, a few hours a month back in your life.

Bench space. A kettle takes up a permanent corner of your benchtop. A boiling tap moves the boiler under the sink and replaces the kettle entirely.

Water waste. Kettle users routinely boil more than they pour. A tap dispenses exactly what you ask for.

Filtration. A standard kettle boils whatever comes out of the mains, including chlorine taste and sediment. A 2-in-1 system pairs the boiler with a 0.5 micron carbon filter, so every cup is filtered.

These aren't financial savings you can put in a spreadsheet, but they're the real reasons most people buy a boiling tap. 

A Few Caveats

A test like this depends on its assumptions, so here's where the numbers might shift:

Your power rate. We used 30c/kWh. If you're on a cheaper plan or a time-of-use tariff, both numbers drop. If you're paying premium peak rates, both go up. The relative difference between tap and kettle stays roughly the same.

Your usage volume. Heavy hot-drink households (15–20 cups a day) tip the maths further in the tap's favour, because the tap's standby cost is fixed while the kettle pays for every reboil. Light users (3–4 cups) tip it the other way.

Tank size. Larger boilers (5L commercial units) carry a higher standby cost. The 2.4L domestic tank we tested is sized for households, not offices.

Scale build-up. Hard water reduces element efficiency over time in both kettles and boilers. Filtered feed water extends the life of the heating element.

So, Is It Worth It?

If you were hoping a boiling tap would save you money on power, probably not, but not by much. Around $6 a month is roughly what it will cost to run a kettle for most households anyway.

The ease for a boiling tap was never really about energy savings. It's about getting a few minutes back every day, freeing up bench space, and getting filtered water in the bargain.

The fact that it costs about the same to run as the kettle it replaces is what makes the decision easy, not what makes it compelling.

If you'd like to see the system we tested, it's our 2-in-1 Boiling & Filtered Tap — 2.4L tank, DUO Brushed nickel tap and 0.5 micron filter.