Why Is My House So Cold in Winter? (And What Actually Fixes It)

Why your house is cold: the five culprits

Australian homes lose heat in winter through five main pathways. The exact split varies by climate zone and building age, but the pattern is remarkably consistent:

• • Ceiling / roof (25–35%): Warm air rises. If your ceiling insulation is thin, displaced, or missing above downlights and manholes, heat streams straight into the roof space.
• • Walls (15–25%): Uninsulated external walls are effectively outdoor air held at arm's length by a thin sheet of plasterboard. In colder climates (Melbourne, Canberra, Hobart), wall heat loss is closer to 25%.
• • Windows (10–30%): Single-glazed aluminium-framed windows are the weakest point in most Australian homes. A single pane of glass has an R-value of about 0.15 — essentially an outdoor surface.
• • Draughts / air leakage (5–25%): Gaps under doors, around window frames, through exhaust fans, and at wall penetrations let cold air in and warm air out. Older homes can lose 15–25% of heat this way.
• • Floors (5–10%): Suspended timber floors over a ventilated subfloor, or a concrete slab with no edge insulation, bleed heat downward — especially in colder states.

Add them up and a typical pre-2000 Australian home can lose 60–80% of its heat through the building shell rather than through ventilation or conductance through an efficient envelope. No heater can economically overcome that.

Room-by-room: where the cold is coming from

Living room

Usually the largest space with the most glazing. North-facing windows are an asset in winter (free solar gain), but east and west-facing single-glazed windows are a liability — they lose heat all night and gain no sun to offset it. Big open-plan living areas with high ceilings compound the problem: more air volume to heat, and stratification (warm air floats above head height).

Fix: Close off unused spaces with doors. Add heavy curtains with pelmets. If renovating, consider double glazing or secondary glazing film. Reverse-cycle heating sized to the actual heat load — not the floor area.

Bedrooms

Often the coldest rooms because they have smaller windows (less solar gain), are on the southern side of the house, and are unoccupied during the day so no heat builds up. Downlights in ceilings cut holes in insulation and create chimney effects.

Fix: Replace downlights with sealed IC-rated LEDs that allow insulation to sit directly above. Add door snakes or weatherstrip bedroom doors. Electric blanket or small reverse-cycle split for nighttime comfort rather than ducted heating the whole house.

Bathroom

Cold because of extractor fans that vent warm air straight outside, often with no backdraft seal. Tiled floors on concrete slabs feel freezing underfoot even when the air temperature is tolerable.

Fix: Install self-closing vents on exhaust fans. Add bath mats or in-slab heating if renovating. A small 2kW heat lamp or towel rail takes the edge off without heating the whole house.

Kitchen

Range hoods are powerful exhaust fans that suck conditioned air out of the house. Open-plan kitchens connected to living spaces drag cold air through the whole area when the range hood runs.

Fix: Use a range hood with the lowest flow rate that still removes cooking fumes. Open a window slightly when cooking to supply makeup air rather than pulling it from the rest of the house. Seal gaps around plumbing penetrations under the sink.

Fix 1: Insulation (the biggest impact)

Insulation works by trapping still air in millions of tiny pockets, slowing the transfer of heat from warm spaces to cold ones. The effectiveness is measured in R-value — the higher, the better.

• • Ceiling: Minimum R4.0 in temperate zones, R5.0–R6.0 in cold zones (Canberra, Melbourne, Hobart). Most pre-2000 homes have R2.0 or less.
• • Walls: R2.5 for new builds; retrofitting walls is harder but achievable during recladding or major renovation.
• • Floor: R2.0 under suspended timber floors; slab edge insulation for concrete slabs.

Cost: Ceiling top-up $800–$2,500 for a typical 150m² home. Wall insulation during renovation $40–$80/m² installed. Floor insulation $30–$60/m².

Payback: Ceiling insulation typically pays for itself in 3–5 years through reduced heating bills. In colder climates, the payback is faster. Find installers in our insulation directory.

Fix 2: Draught sealing (the cheapest win)

A draught is uncontrolled air leakage — and in most Australian homes, the total leakage area is equivalent to leaving a window open year-round. The good news: it's cheap and easy to fix.

• • Door and window weatherstripping: $5–$20 per door/window. Foam or brush seals stop cold air entering around frames.
• • Door sweeps / snakes: $10–$30. Block the gap under external doors and even internal doors to unused rooms.
• • Exhaust fan covers: Self-closing vents prevent warm air escaping through bathroom and laundry fans when not in use.
• • Gap sealing: Expanding foam or caulk around plumbing penetrations, skirting boards, and architraves.
• • Chimney balloons: If you have an open fireplace you don't use, a chimney balloon ($30–$50) stops a massive heat leak straight up the flue.

Total cost for a DIY draught-proofing job: $100–$400. Professional blower-door-guided sealing: $800–$2,000. Typical savings: 10–20% on heating bills. Check available rebates by state — some states subsidise professional draught sealing.

Fix 3: Windows and glazing

Single-glazed aluminium windows are common in Australian homes and are essentially outdoor surfaces. On a cold night, the inner pane can be below 10°C, creating a cold radiant surface that makes you feel chilly even if the air temperature is 20°C.

• • Heavy curtains with pelmets: The cheapest option. Closed curtains trap a layer of still air and cut heat loss through glass by 25–40%. The pelmet (or a box cornice) stops the warm air from sliding down behind the curtain and out the bottom.
• • Secondary glazing film: A transparent film applied to the inside of window frames, creating a still-air gap. Cost: $5–$15/m² DIY. Reduces heat loss by 30–40%.
• • Double glazing: Two panes with an argon-filled gap. Cost: $400–$800/m² installed. The gold standard, but expensive to retrofit.
• • Thermal-break aluminium or uPVC frames: Standard aluminium is a thermal bridge — it conducts cold straight through the frame. Thermal-break or uPVC frames fix this.

Priority: Start with the rooms you occupy most. Living room north-facing windows need curtains you can open during the day for free solar gain and close at night. Find glaziers in our window and glazing directory.

Fix 4: Thermal bridges and overlooked leaks

A thermal bridge is a path heat can travel easily — like a highway for heat escape. Common ones in Australian homes:

• • Steel framing: Steel studs transfer heat 300× faster than timber. If your walls feel cold to the touch, the framing may be acting as a thermal bridge.
• • Concrete slab edges: An uninsulated slab edge is a direct connection between the warm floor and the cold ground outside.
• • Downlights: Halogen downlights create a hole in ceiling insulation and vent warm air into the roof space. Switch to IC-rated sealed LEDs.
• • Skylights: Beautiful, but often poorly sealed and single-glazed. Consider tubular skylights with diffusers instead.

These are harder to spot than obvious draughts but can account for significant heat loss. A NatHERS Existing Homes Assessment uses thermal modelling to identify which bridges are costing you the most.

Fix 5: Heating system rightsizing

If you've fixed insulation, draughts, and glazing and the house is still cold, the problem is probably an undersized or inefficient heater. But don't upsize the heater first — fix the shell, then size the heater to the reduced heat load. A well-sealed home needs a smaller, cheaper heater.

• • Reverse-cycle air conditioning (heat pumps) are now the most efficient heating in every Australian climate zone. COP 3–5 means 3–5 units of heat per unit of electricity.
• • Ducted gas heating is 60–80% efficient and becoming more expensive to run as gas prices rise. If your ducts run through an unconditioned roof space, you're losing 20–30% of heat before it reaches the rooms.
• • Portable electric heaters (radiant, oil-filled, fan) are 100% efficient at turning electricity into heat but expensive to run for whole-home heating. Best for spot heating one room.

Rule of thumb: For every 1 star your NatHERS thermal rating improves, your heating energy requirement drops by roughly 10–15%. A 2-star home might need 15kW of heating. A 6-star home of the same size might need 6–8kW. Find HVAC installers in our HVAC directory.

The right order to fix a cold house

Don't do everything at once. Follow this priority order for maximum comfort per dollar:

1. Draught seal ($100–$400 DIY) — cheapest, fastest return, immediate comfort lift.
2. Ceiling insulation top-up ($800–$2,500) — biggest single impact on winter heat loss.
3. Window treatments ($200–$1,000 for curtains + pelmets) — especially east, west, and south-facing rooms.
4. Wall insulation during any recladding or major renovation — hard to retrofit otherwise.
5. Rightsize heating after the shell is fixed — you'll need less capacity than you think.

For a detailed retrofit guide with cost ranges and star-rating improvements, see our article on how to improve your NatHERS star rating.

How a NatHERS assessment finds the real culprits

A NatHERS assessment doesn't guess — it models your home's heat flows using accredited software and CSIRO climate data for your exact location. The software calculates:

• • How much heat escapes through each surface (ceiling, walls, windows, floor)
• • How much free solar heat enters through north-facing glass
• • How much heat is lost through air leakage (modelled as infiltration)
• • What heating load is required to maintain 20°C inside on the coldest design day

The output is a 0–10 star thermal rating and a detailed report showing which elements are dragging your score down. For existing homes, the new NatHERS Existing Homes Assessment pathway (agreed March 2026) means you can now get a certified rating without needing full construction drawings.

Why this matters for winter comfort: The same elements that lower your NatHERS star rating are the ones making your house cold. A 2-star home will always be expensive and uncomfortable to heat. A 6+ star home holds warmth with minimal heating input.