Hot water sizer

What cylinder & system suit your home?

A 60-second, NZ-specific tool — including running-cost comparisons across electric, heat pump, solar and gas.

NIWA cold-water temps Right-sized per household Free & independent
Choose your mode

Hot water is typically 30% of a Kiwi power bill. Get this right and you'll save more here than anywhere else in the home.

Tell us about your household

Recommended cylinder

—

—

—L / day
—kWh / yr
—Best tech

—

Recommended for you
Featured hot-water heat pumps and supplier offers, hand-picked for your household.
Finding matching offers…
From verified Power Buddy Experts in your area.
Compare supplier offers Independent, no retailer spin.
Compare hot water systems

We'll compare electric cylinder, hot-water heat pump (e.g. Carrier Blue), solar hot water and LPG instant gas for your household — upfront cost, annual running cost, and 15-year lifetime cost.

We've carried these across from your Cylinder Size inputs — adjust anything below to override.
Default is the NZ April 2026 average. Override if your bill says otherwise.
—

Lifetime cost = upfront install + (annual running × 15 yrs). Heat pump COP and solar fraction already factor in NZ region. Real quotes vary with brand, install complexity and any switchboard work.

Recommended for you
Featured hot-water heat pumps and supplier offers, hand-picked for your household.
Finding matching offers…
From verified Power Buddy Experts in your area.
Compare supplier offers Independent, no retailer spin.
What is your hot water actually costing?
We've carried these across from your Cylinder Size inputs — just pick your current system below.
—Now / year
—kWh / year
—HPHW / year
—Yearly savings
—

—

Recommended for you
Featured hot-water heat pumps and supplier offers, hand-picked for your household.
Finding matching offers…
From verified Power Buddy Experts in your area.
Compare supplier offers Independent, no retailer spin.
How we size and cost it
  • Daily hot-water demand: weighted per person (adults / teens / kids), shower habits, plus extras for baths, dishwasher and hot-wash laundry
  • Energy: kWh = L × ΔT × 1.163e-3, with NZ region-specific cold-water inlet temps (~12 °C Auckland to 7 °C Southland), heated to 60 °C
  • Cylinder standing losses included for electric and heat-pump systems (lower for new wrapped tanks)
  • Heat pump COP averaged across NZ regions (warmer = higher COP); solar fraction tuned to NZ peak-sun hours per region
  • Costs are typical mid-2026 NZ supply & install ranges across Carrier, Mitsubishi, Apricus, Rinnai and Bosch

Hot water — frequently asked

A typical 4-person Kiwi household uses 200–300 L of hot water a day. A 250–300 L electric or gas cylinder fits most homes; for hot-water heat pumps the same household is usually well-served by a 270 L unit because they reheat slowly but efficiently. The sizer above tailors the recommendation to how many showers per day, whether you have a bath, and whether you do laundry in hot water.

For most Kiwi homes — yes. A modern hot-water heat pump uses about a third of the power of a standard electric cylinder (COP 3+ in Auckland, ~2.5 in Southland), saving $400–$700 a year. Payback over a standard cylinder is typically 5–8 years; over a gas system it's faster once you include the daily fixed gas charge. They also halve your hot-water CO₂ footprint.

In 2026 NZ pricing: hot-water heat pump is cheapest (~$300–$450/yr for a 3-person home), then mains gas (~$550–$750/yr including daily charge), then standard electric (~$700–$950/yr), then bottled LPG (~$900–$1,300/yr). Solar hot water beats them all on a sunny roof but the up-front cost is high. The sizer above shows your specific number for each option.

Mains-pressure stainless steel cylinders typically last 15–20 years; copper low-pressure cylinders 20–25 years; enamelled steel (with a sacrificial anode replaced every 5 years) 15–18 years. Heat-pump hot water units have a 10–15 year design life. If yours is over 12 years and starting to leak, plan ahead — emergency replacements always cost more than planned ones.

Yes — for older A-grade or B-grade cylinders, a $40 wrap (plus pipe lagging on the first metre of pipe) typically saves $80–$150 a year by reducing standing heat loss. Modern A++ rated cylinders are already well-insulated and the wrap saves much less. If you can hear your cylinder cycling on at 2 a.m. when no-one's drawing water, it'll benefit from a wrap.