Passive heating – harness the sun
By combining good design with effective insulation, you can collect and store the sun's energy to provide your home with warmth day and night, throughout most of the year.
The two key aspects of passive heating are to capture the right amount of sunlight through your windows and then to manage that free heat so that it keeps your home at a comfortable temperature. This is achieved by using a combination of smart design, good insulation and features that prevent overheating.
Using the sun to heat your home can slash your heating costs, reduce condensation and dampness, and make your home healthier and more comfortable.
Passive heating can be incorporated into new homes, renovations or existing homes of all types. However, it is much easier and more cost-effective to incorporate at the early design and planning stages of a new build. In some homes, passive heating alone will maintain stable temperatures year-round without any need for supplementary heating. Others may need additional heating in winter – this supplementary heating will be far more effective in a home that uses passive heating principles.
As well as reducing heating costs, passive heating is by far the most environmentally friendly way to heat your home. Other forms of heating such as gas and electricity generate greenhouse gases and other harmful emissions when produced by burning fossil fuels.
Passive heating should be part of an overall approach to passive design. Depending on your situation (climate, house style, personal preferences, etc) it is most effective if you incorporate the principles of both passive heating and passive cooling.
Passive cooling has more information.
Is passive heating right for me?
Using the sun to heat your home in combination with good insulation is suitable for any type of home, on any site, in any location, provided it has reasonable access to sunlight. Stand-alone houses, apartments and townhouses can all benefit.
Costs and benefits
The most important elements in capturing and making the most of the sun's warmth are good insulation and smart design. It doesn't have to cost more, for example, to make sure your main windows face the sun or, if your site allows, to use an insulated concrete floor for thermal mass to retain heat instead of a timber one.
There may be some costs involved in passive heating – for example, for better insulation (with a higher R value) or thermally broken window frames for double glazing. These will pay for themselves over time because less energy will be needed to heat your home resulting in lower power bills.
In general, if you incorporate passive heating principles in the planning stage, construction costs shouldn't be significantly greater than those for a conventional home.
When you're budgeting for passive heating, the highest priorities should be including exposed thermal mass (eg an insulated concrete slab floor) in sunny areas, well-placed and sized windows, and better insulation including improved window frames. Exceeding Building Code minimum requirements, especially the thermal performance of your double glazing and window frames in the colder regions is recommended to make the most of passive heating.
When you should think about passive heating
Planning a home or renovation
Passive heating principles can influence every aspect of the design of your home. Ideally, you'll start thinking about it before you've bought a property or started planning your home or renovation. Passive heating should be considered alongside passive cooling and ventilation.
In your existing home
Passive heating can be improved in an existing home without making major alterations. The most obvious way to achieve this is by installing extra insulation in your ceilings and under floors. If you are relining walls for any reason, consider insulating them when you do – talk to your local council about the rules. You can also reduce heat loss by double glazing your windows, replacing poorly performing windows and sealing up draughts.
If you make alterations to your home you can add windows to capture the sun where and when you want it most. Your advantage compared to a new house is that you know exactly how you are using your home and when and where the sun appears on your site. So you can predict quite well how any window additions will affect the solar access to the interior.
With passive heating, the first step is getting the sun's warmth into your home, mainly during the cooler seasons. To make the most of the sun, the main living areas of your home (or any rooms you use a lot) need to face within approximately 30° of true north (where the sun is at noon – not accounting for daylight saving). You will need to plan your windows so that the majority of your glazing faces in a north direction.
Once you've got the sun's warmth into your home, you need to keep it in there for as long as possible. Heat escapes by passing through the ceiling, walls, floor and windows. To keep warmth in, you'll need to block off its escape routes: insulate, take steps to reduce heat loss through windows (with sealing, double glazing and lined curtains) and block off draughts.
Insulation in your home is essential for effective passive heating. It:
- keeps heat in on cold days
- prevents too much heat from getting in on hot days
- reduces condensation and dampness – cold air holds less moisture so it will condense on cold surfaces, such as non-thermally broken aluminium window frames and uninsulated walls and ceilings.
Insulation is one of the best investments you can make to improve the quality of home life. No matter where you live and what type of home you have, the ongoing benefits of good insulation will far outweigh the costs.
There are legal minimum requirements for insulation in new homes and renovations – it's worth exceeding these requirements to get a warmer, more comfortable home. This is particularly important because it is often very difficult or impractical to improve insulation later on, eg in skillion ceilings or walls.
If your home is well insulated, the biggest source of heat loss will be through glazed areas (ie windows, skylights and glass doors). You can reduce this by:
- using close-fitting, floor length heavy drapes with pelmets
- using double glazing with low-e (low-emittance) glass with argon filling
- using timber, polyvinyl chloride (PVC) or thermally broken aluminium window frames
- designing larger windows on the northern side, and smaller windows on the southern sides of the house
- locating windows so that eaves let sun into the house in winter.
Good orientation is a key aspect of creating a home that stays warm and comfortable year-round. Insulation is also vitally important.
House orientation has more information.
Draughts are caused by air moving from a warm area to a cold area, creating a breeze. They contribute to heat loss. Typically, draughts can come from:
- gaps between frames and walls during construction
- gaps around badly fitting windows and doors
- inability to shut off heated areas
- chimneys and flues.
Stopping draughts is one of the simplest and most cost-effective steps toward conserving heat.
To prevent heat loss:
- locate rooms that are used least such as garages, bathrooms and laundries to the south - they'll provide a buffer, preventing heat loss in living areas
- use 'air locks' at external entrances to your home, to keep cold draughts out – entryways, laundries and attached garages can all function as air locks.
The shape of your home will influence heat loss. For example, a multi-level home will be easier to keep warm because it has less roof surface through which to lose heat. The top storey will also be warmer because heat rises up through the house.
Keep the floor footprint as simple as possible. The less corners a house has, the less thermal weak points there are and the more weather-tight the roof is likely to be.
You can store the sun's warmth by using materials with high thermal mass (materials that are good at absorbing and storing heat). These materials are usually heavy – such as concrete and brick – and are used in floors or walls.
Used properly – the right amount in the right place, with proper insulation – the high thermal mass materials will absorb heat during the day and slowly radiate it out as the temperature drops in the afternoon or evening. This will reduce the amount of heating you will need to do.
Thermal mass for heating and cooling has more information.
Achieving the right balance
It's vital to get all aspects of passive heating working together. If you consider only one aspect, you risk not making the most of the sun's warmth and your home not being as comfortable as it could be. For example, if you install large windows on the north wall of your home but don't think about how to store or conserve heat, you might find you're hot during the day and then cold when the temperature drops sharply after the sun goes down.
If you install a lot of north and west-facing glazing you will need to include shading to reduce or summertime overheating.
Passive cooling has more information.
If you do nothing else, at least make sure your ceiling and walls are well insulated – you'll get a more comfortable home and lower power bills.