Introduction to the heating assessment tool

The heating assessment tool helps you calculate the minimum heating capacity required for heaters in your rental home under the healthy homes standards. As part of these standards, landlords must provide a fixed heater (or heaters) that can heat the main living room. The heating assessment tool helps you calculate the minimum heating capacity required for heaters in your rental home under the healthy homes standards. As part of these standards, landlords must provide a fixed heater (or heaters) that can heat the main living room. 

This tool is referenced in the Residential Tenancies (Healthy Homes Standards) Regulations 2019 as the ‘heating capacity calculator’. If you use this tool in good faith by using accurate informaton, you can rely on the tool to deliver correct results based on that information. You’re also entitled to rely on the assumptions the tool makes, unless you know these assumptions are wrong. 

Read our full disclaimer. (external link)

The tool provides a report that shows the minimum heating capacity you need. You can use it to check if your current heating is sufficient to meet the standard, or if you need to install a new heater. The report can also help prove a rental home meets the heating requirements in the healthy homes standards.

More information about the healthy homes standards (external link)

The tool asks a series of questions about:

  • what region your home is in (to understand the local climate)
  • how much space you need to heat
  • what surfaces (walls, windows and doors) heat can escape through
  • how well these surfaces are insulated.

Your privacy

When using the tool you’ll need to provide an email address if you want to save your progress and finish your assessment at a later time. We won’t store or share your email address. We’ll send a link to this address so you can access the tool and the information you’ve entered so far. This link will expire after 60 days and any information you’ve input will be cleared. For more information read our full privacy statement. (external link)

How to use the tool and gather the information you’ll need

The tool needs several pieces of information to provide accurate results. This guide will help you prepare the information you need before you start using the tool. This will help avoid the need to stop part-way through. The tool needs several pieces of information to provide accurate results. This guide will help you prepare the information you need before you start using the tool. This will help avoid the need to stop part-way through.

Overall you’ll need to:

  • gather information about the property’s age and location 
  • measure the main living room and calculate areas
  • assess insulation and replace estimates where you can.

If your rental home layout is complex to measure, or you find the calculations difficult, an industry expert like a home performance assessor can calculate the required heating capacity for you. The more accurate your information is, the more accurate your report will be.

The formulae that industry experts may prefer to use for manual calculation can be found in the Residential Tenancies (Healthy Homes Standards) Regulations 2019.

Healthy homes standards heating capacity formulae (external link)

Find building practitioners in your area:

Search the licensed building practitioners register (external link)

Search the plumber, gasfitter and drainlayer public register (external link)

Search the electrical workers register (external link)

For more information or advice when installing heaters, woodburners or heat pumps, visit:

Community Energy Network (CEN) (external link)

New Zealand Home Heating Association (external link)

Master Plumbers (gasfitters) (external link)

Climate Control Companies Association of New Zealand (CCCANZ) (external link)

Home Performance Advisors (HPA) (external link)

1. Gather information about the property’s age and location

The council area that your rental home is located in helps the tool understand your local climate – for example, how cold it gets in winter. You need more heating capacity if you live somewhere cold. Some heat pumps struggle to perform at cold outdoor temperatures just above freezing point. If you live somewhere cold and your heaters include a heat pump, you’ll need one that performs well at cooler temperatures.

The date your home was built tells us what building standards apply. The tool will use this information to make an assumption about the insulation of your walls, windows, ceilings and floors.

Your local council can help you search for property information. If you can’t find when your home was built, choose the earliest year that might apply. If you know your home was built to building standards for a specific year, use that year.

2. Measure the main living room and calculate areas

You’ll need to measure the main living room and any connected spaces that are always open to it, which cannot be closed off with windows or doors. Then you’ll need to calculate the areas of walls and floors. The tool will assume your ceiling area based on the size of the living room floor.

If you’re planning to renovate your rental property to make the main living room bigger, you should use measurements based on the future layout. This may overestimate the level of heating you currently need but will make sure your heating device will meet the healthy homes standards.

This section shows you what to measure and how to calculate the areas you need. These examples are written for floors. You can use the same calculations for walls or other surfaces.

Which room is the main living room?

The heating requirements of the healthy homes standards apply to the ‘main living room’ of a rental home. A living room can be any habitable space that can be used for general everyday living — for example, a lounge room, dining room, sitting room or family room. Living rooms can also include multi-use spaces like a studio apartment or open-plan kitchen/dining room. If you have more than one living room, use the largest living room.

What’s included in the living room?

In the tool, ‘living room’ means the whole space a living-room heater must be able to heat. You will need to include any other connected space that is always open to the living room, such as an open-plan kitchen, hallway or stairwell. Spaces are always open to each other if there is no solid barrier between them. If you can close a door or window, you don't need to include the space beyond it.

HAT guide living room 1

In the tool, ‘living room’ means the whole space a living-room heater must be able to heat. You will need to include any other connected space that is always open to the living room, such as an open-plan kitchen, hallway or stairwell. Spaces are always open to each other if there is no solid barrier between them. If you can close a door or window, you don't need to include the space beyond it.

HAT guide living room 2

 

How do I measure accurately?

When you measure lengths, ignore small details like skirting boards. You can also ignore small features (like pillars) that stick out from the wall, and any partial dividing walls.

HAT guide measure accurately

Your measuring tape may show millimetres (mm), centimetres (cm) or metres (m). 1000mm = 100cm = 1m. You will need to enter your measurements in the tool in metres.

If you already have plans that show the measurements, you can use those measurements instead. If the plans use imperial measurements (feet and inches) you’ll need to convert them into metric measurements (metres).

How do I calculate the area of rectangles?

Measure the length of the room at its longest point, and the width of the room at its widest point. Length x width = area.

HAT guide calculating area of rectangle

How do I calculate the area of other living room shapes?

Your living room may be a combination of rectangles, such as an L shape. You can break the shape down into several rectangles and add up their areas.

HAT guide other living room shapes

Or you can draw the shape on a grid and calculate the area by counting squares.

 

HAT guide grid

Draw a grid or use gridded paper. Use each square to show 1m.

Measure the room and draw the wall lengths onto the grid. In the example you can see the measurements that are not whole metres cover part of a square.

Add up the squares the room covers. This gives you the area in square metres. If the room covers part of a square, you can calculate the exact area or count the whole square. Counting the whole square is easier but will overestimate the area.

 In this example, counting the whole squares gives you an area of 10m2. The actual area is closer to 9.5m2.


If you want to keep things simple, you can even replace the complex shape of your floor with a rectangle that fully encloses it. This will overestimate the area.

How do I calculate the area of complex shapes?

Your living room may include more complex shapes, such as curves or triangles. Break down the living room into shapes you can calculate the area for, and then add the areas up.Your living room may include more complex shapes, such as curves or triangles. Break down the living room into shapes you can calculate the area for, and then add the areas up.

Use these formulas or look up the formulas for other shapes.

  • Triangle: ½ x base x height = areaMeasure the height of the triangle at right angles to the base. 
  • Circle: 3.1416 x radius x radius = areaThe radius is the distance from the centre of the circle to the edge.
  • Part circle: circle area x proportion of full circle (eg ½ for a semicircle) = area

HAT guide calculating complex shapes

If you prefer, you can draw the shape on a grid and estimate the area by counting squares.

How do I identify internal and external walls, floors and ceilings?

External walls, floors and ceilings are more important than internal ones for trapping heat. The tool will need you to specify whether walls, floors and ceilings are internal, external or a mix.

A wall, floor or ceiling is internal if it has another conditioned space behind, below or above it. A conditioned space is an area that’s designed to be heated or cooled, like a kitchen, hallway, bathroom or other room. This applies even if it is a different home or a neighbour’s apartment.

A wall, floor or ceiling is external if it does not have a conditioned space behind, below or above it. This could include property foundations, a garage, roof space, subfloor space or the outdoors.

If a wall, floor or ceiling is a mix of internal and external, you can call it all external or you can enter the details for each part separately. If you call it all external the tool may overestimate the level of heating you actually need. This ensures the heating capacity will be enough to meet the healthy homes standards. Separating the wall, floor or ceiling into internal and external parts will give you more accurate results.

HAT guide identifying walls

HAT guide identifying floors

HAT guide identifying ceilings

 

How do I measure windows, skylights and doors?

You only need to measure windows or other glazing in external walls or doors. You don’t need to measure windows or other glazing for internal walls, as the tool will treat them the same as the surrounding wall.

HAT guide identifying walls

Measure the full size of windows and skylights, including frames. If several similar windows or panes are located together, you can treat them as one large window and give the combined size.

HAT guide measuring windows

HAT guide measuring skylight

You don’t need to measure any doors, as we treat them the same as the surrounding wall. You need to measure any windows or other glazing in external doors.

HAT guide measuring door glazing

3. Assess insulation and replace estimates where you can

Calculating a room’s heating needs is complex. The tool lets you simplify the calculations for areas, and its calculations for volumes make some assumptions based on this.

In some places the tool estimates a suitable value based on information you’ve provided. For example, it will assume your home has the minimum insulation building standards required but not more. You can use the estimate or you can provide a specific value to be more precise.

Where these estimates are not exact, the tool picks a safe value so you know the heating calculated by the tool will be enough. The tool might recommend more heating than you actually need. The more accurate the information is that you provide, the less the tool will overestimate the heating you need. If you know you have an R-value that is lower than the tool estimates you must enter the correct lower value.

What is an R-value?

An R-value is a measure of how well a building material traps heat. Based on the age of a home, the tool will estimate whether the walls, floors, and ceilings have insulation and how good it is (the R-value). The tool will assume that if any insulation is present that it’s in a reasonable condition.

The total R-value of a surface involves all its different layers. For example, if your wall’s layers are plasterboard, insulation and weatherboard, the R-value for each layer contributes to the total R-value. Even if your wall is not insulated, it will still have an R-value.

When should I enter my own R-value?

You can use the R-value estimated by the tool or you can enter your own R-value. For example, if your home has been upgraded with better insulation since it was built, entering the new R-value will provide a more accurate result.

The tool may estimate an R-value assuming that the property does not have insulation because of the year it was built. It’s usually easy to check under the house or in the roof space to see if insulation has been installed. All rental properties should have ceiling and underfloor insulation installed by 1 July 2019 where reasonably practicable. Some properties may not have been upgraded so the tool assumes insulation levels based on the year it was built.

How do I assess my insulation?

To assess the insulation at your property you can physically look, engage a professional to do an assessment, or check the council building file. If you're not sure of the location, type and condition of the insulation, seek advice from a professional insulation installer. To assess the insulation at your property you can physically look, engage a professional to do an assessment, or check the council building file. If you're not sure of the location, type and condition of the insulation, seek advice from a professional insulation installer.

Assessing insulation

The tool will also assume that any insulation present is in a reasonable condition. If your insulation isn’t in reasonable condition you may need to upgrade it, to make sure it meets the healthy homes standards.

Healthy homes standards insulation requirements

If you’re checking insulation at a property it’s important to do this safely, particularly if there’s existing foil insulation. The installation or repair of foil insulation is banned in all residences including rental homes.

Checking insulation safely

Rating form

Did you find this information helpful?

For general enquiries please contact us