How to reduce heat loss through downlights

A downlight is a light fixture that is installed into the ceiling. When installed it appears to have light shining from a hole in the ceiling, concentrating the light as a broad floodlight or narrow spotlight. Multiple downlights in a house can be an attractive lighting option; however they also introduce some significant energy efficiency and safety concerns.

Insulation and downlights - things to think about

Downlights use more energy than traditional hanging pendant lights

Downlights don't reflect any light off the ceiling like traditional hanging lights so more bulbs are needed to light the room. In fact a lot of the light is going up into your ceiling through vents in the light fitting which allow hot air to dissipate. Because of this you may use 2-3 times the electricity to light a room using downlights rather than with traditional lighting.

Vented downlights are effectively holes in your ceiling. Warm air in the living spaces below can move directly through the downlight fittings, creating draughts and greatly reducing how well the insulation works, and therefore the temperature in the room below. Lots of downlights will also increase the amount of heating required to keep a house at healthy temperatures.

Downlights and ceiling insulation don't mix!

Downlight transformers can get very hot and represent a fire risk, especially if ceiling insulation is placed (or blown) over the downlight fitting or transformer. This risk should be taken seriously.

The New Zealand Standard that guides how insulation should be installed (NZS 4246:2006) requires a 150mm gap between insulation materials and downlight components (unless there is written documentation from the  manufacturer that a lesser clearance is acceptable). Clearances are also recommended between other building members (such as ceiling joists) and downlight fittings.  

Ensuring there is a clearance between downlights and your insulation improves safety but greatly reduces how well your insulation will work because big gaps are left in your insulation.

Options for dealing with downlights

• Replace downlights with light fittings that are surface mounted or hang down from the ceiling Consider replacing the down lights with pendant lighting, or spot light fittings that protrude down from the ceiling. This option allows you to fully insulate the ceiling area above but it requires sealing and plastering the holes left by the old down lights which can be a big job.

• Replace standard incandescent bulbs with energy saver compact fluorescent lamps (CFL's). These will use less electricity and reduce heat loss. It is important to make sure that the CFL is designed for the downlight fitting so that light is reflected back down into the room effectively.

• Heat Cans (supplied by electrical wholesalers) Heat Cans could be placed around downlights, which usually allow you to insulate safely up to (but not over) the can. These products are designed to minimise the risk of fire. However they will not significantly reduce direct heat loss because they are usually made of materials that easily transfer heat, cannot have insulation fitted over them, and may not allow you to insulate more closely than your existing ceiling insulation.

• Install alternative downlight fittings Another option is to install replacement downlights which can have insulation fitted closer to the downlight than the 150mm downlight clearance recommended in the Standard.

Tips for talking to lighting advisors or retailers about replacing downlight fittings

If possible, identify the specifications of your existing bulbs/downlight fittings. This includes the wattage of each bulb, plus the brand and size of the downlight fitting. It might help to show lighting advisors photos of the existing fittings, plus an example of the bulb your currently use in the fitting. This should help lighting sales advisors identify:

• the clearance required for insulation around existing downlights (usually 150mm diameter around older style fittings)
• if there is heat lost through the existing fitting
• how much energy each bulb uses per hour
• a suitable replacement.

When discussing replacement fittings ask

• if they have any "closed" (the area of the vent is no more than 5% of the area of the hole cut in the ceiling) or "restricted" (the area of the vent is between 5 and 15% of the hole cut in the ceiling) rated light fittings. This type of fitting has reduced heat loss compared to older fittings.
• how closely the insulation can be fitted around the replacement light fittings.
• how much electricity the replacements bulbs use compared to your existing ones.

This will help you to work out if the different products they suggest can reduce heat loss and energy use compared to your existing fittings and if it is worth your while replacing them.

For more information about lighting

Visit http://www.rightlight.govt.nz/. There is lots of very good information about lighting on this website, or go to your local library and check "Consumer" magazine for their reports on lighting for free. The March 2010 edition has a report on downlights.