Healthy Homes Heating Standard NZ: Calculations, Heater Types and the Assessment Tool

What the Heating Standard Requires

The main living room of every rental must have one or more fixed qualifying heaters capable of raising the indoor temperature to at least 18°C. The required heating capacity in kilowatts depends on your room's dimensions, construction type, and geographic location — not on a landlord's best guess.

Portable heaters do not count. Neither do open fires, unflued gas heaters (LPG cabinet heaters), or electric heaters without a thermostat. The standard is specific about what qualifies and what does not.

Qualifying vs Prohibited Heaters

Qualifying heaters:

• Fixed heat pumps with thermostat
• Wood burners or pellet fires (with current building consent where required)
• Flued gas heaters
• Direct-wired electric heaters of at least 1.5 kW with thermostat — but only if the calculated requirement is 2.4 kW or less

Prohibited heaters:

• Open fires
• Unflued combustion heaters (LPG cabinet heaters, portable gas)
• Electric heaters without a thermostat
• Portable plug-in heaters of any kind

If your property has an open fire as the sole heat source, it does not comply. An unflued gas heater — the kind that runs on a bottled LPG cylinder — is banned from counting toward the standard regardless of its output. These heaters release combustion byproducts (moisture and carbon monoxide) directly into the living space.

Using the MBIE Heating Assessment Tool

The official Heating Assessment Tool on the Tenancy Services website calculates the required heating capacity for your main living room. You enter the room dimensions, ceiling height, wall and window construction, insulation details, and your territorial location. The tool applies the statutory formula from Schedule 2 of the Regulations and gives you a kilowatt figure.

When you enter accurate data in good faith, the tool's output is legally presumed correct under Regulation 10(2). Save the report as PDF evidence for your compliance file.

The formula accounts for transmission heat loss through walls, ceiling, floor, and windows, plus ventilation heat loss. A standard dwelling uses the formula: h (kW) = (t + v + (f × 40)) / 1000, where t is transmission loss, v is ventilation loss, and f is the floor area in square metres. Modern dwellings (built to recent Building Code standards) and qualifying apartments of three or more storeys with six or more units use a revised formula with a 1.2 multiplier: h (kW) = ((t + v) × 1.2) / 1000.

You do not need to calculate this by hand. The online tool does it for you. What you do need is accurate room measurements.

The 80% Tolerance Rule

If an existing qualifying heater was installed before 1 July 2019 and the required capacity exceeds 2.4 kW, a tolerance applies: the heater only needs to provide at least 80% of the calculated requirement. If the heater provides less than 80%, you need to top up with an additional qualifying heater or replace it entirely.

For heaters installed after 1 July 2019, no tolerance applies — the full calculated capacity must be met.

How to Calculate Your Heating Requirement

1. Measure the main living room: length, width, and ceiling height in metres
2. Note the wall construction type (timber frame, concrete block, brick veneer)
3. Measure or estimate the total window area in the room
4. Check your ceiling insulation type and condition
5. Find your property's territorial external temperature from the tool's location lookup
6. Enter all values into the Heating Assessment Tool
7. Compare the tool's required kW figure against your heater's rated output (on the rating plate or product label)

If your heater's rated output meets or exceeds the required figure, save the tool report and note the heater's make, model, and capacity in your compliance statement.

Alternative Compliance Pathways

The Heating Assessment Tool does not work well for every property. Complex layouts, passive solar designs, or non-standard construction can produce unreliable results. Three alternatives exist:

Specialist assessment (Regulation 10A): A suitably qualified specialist — such as a Chartered Professional Engineer — provides a written assessment certifying that the installed heating is sufficient to maintain 18°C in the main living room.

Geothermal heating (Regulation 10B): Recognised as compliant provided heat is delivered directly into the main living room.

Certified passive buildings (Regulation 11): Exempt from standard calculations if certified under recognised passive house criteria.

Heat Pump Sizing: Over-Spec, Not Under

Forum advice from experienced NZ landlords consistently recommends over-specifying the heat pump. The Heating Assessment Tool calculates based on reaching 18°C from a design external temperature — which in some South Island locations can be as low as -2°C. If the tool says you need 3 kW, installing a 4.5 or 5 kW unit provides a compliance margin that accounts for degradation and edge-case weather.

The NZ Healthy Homes compliance guide includes a room measurement worksheet and a step-by-step walkthrough of the Heating Assessment Tool to help you gather the right data before you start the calculation.

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