How to Keep Your Conservatory Warm and Cosy

Conservatories cool fast because glass and polycarbonate are poor insulators, metal frames conduct heat straight outside, and many were built before modern thermal standards applied to extensions. The roof alone can account for half the heat loss.

The fix is a two-step process: plug the leaks in the building envelope, then choose efficient heating for the space you’ve tightened. Quick wins like sealing gaps and adding blinds work this week. Roof upgrades and underfloor heating are long-term investments that pay back in comfort and lower bills.

How to Keep Your Conservatory Warm and Cosy

Stop heat escaping before you add more of it. Insulate the roof first, seal drafts around doors and windows second, then insulate the floor—only after those steps will a heating system work efficiently and affordably.

A conservatory is mostly glass, and glass conducts heat out faster than any other part of your home. Single glazing has a U-value around 5.0 W/m²K, meaning it loses heat five times faster than an insulated wall. An uninsulated polycarbonate roof performs even worse. The result: you heat the garden, not the room.

Bare glass also lacks thermal mass. Brick and plaster absorb warmth during the day and release it slowly; glass does not. That is why a conservatory feels colder than other rooms at the same temperature, and why it swings from freezing at night to overheating in direct sun.

1. Insulate the roof
   The roof accounts for the largest share of heat loss because warm air rises and glass or polycarbonate does nothing to stop it. Retrofit insulation panels, thermal roof blinds, or a solid tiled roof replacement will cut loss by 27 to 82 percent depending on the system.
2. Seal walls, doors and windows
   Drafts around door frames, window seals and roof joints let cold air in and push warm air out. Draft excluders and fresh weatherstripping are cheap, fast fixes that make an immediate difference.
3. Insulate the floor
   Cold rising from a concrete slab or suspended floor chills your feet and draws warmth downward. Insulated boards, thick rugs, or underfloor heating address the problem at the source.

Insulate the Roof to Stop Heat Escaping Upward

Older conservatory roofs—polycarbonate sheets and single-glazed glass—provide almost no insulation. Polycarbonate has a U-value around 3.0 to 4.0 W/m²K, and single glass sits near 5.0 W/m²K. For comparison, a modern insulated house roof achieves 0.16 W/m²K. The conservatory roof is where most of your heat goes.

Four routes cut that loss, each with different cost, disruption and performance. Internal insulation kits like the CHRIS Insulation System improve roof U-values by up to 82 percent and reduce heat transfer by up to 32 percent, fitting between the glazing bars without removing the existing roof. Thermal roof blinds—pleated or honeycomb designs—reduce heat loss by up to 27 percent by trapping a layer of still air against the glass. Upgrading the glazing to Low-E coated double or triple glazing cuts U-values to around 1.1 to 1.4 W/m²K. Replacing the roof entirely with a solid tiled system brings performance in line with the rest of the house, around 0.18 W/m²K, but costs the most and blocks overhead light.

Blinds and internal kits are weekend or single-day jobs. Glazing upgrades take several days and require scaffolding. A solid roof replacement can run two weeks, needs building control approval, and may require foundation reinforcement if the structure was not designed for the weight.

Seal Drafts Around Doors, Windows and Roof Joints

Air leaks waste more heat than most owners expect. A single unsealed gap around a door frame or along the conservatory-to-house joint can let out as much warmth as several square feet of single glazing. Finding and sealing them takes a weekend and costs less than running a heater for a month.

1. Find the leaks
   On a windy day, hold a damp hand near door edges, window frames, roof joints and the wall where the conservatory meets the house. You will feel cold air moving. Check locking mechanisms: a door that does not pull tight when locked leaves a gap all the way around.
2. Seal window and door frames
   Run a bead of clear silicone sealant along gaps between the frame and the wall, and along roof joints where panels meet the structure. For opening windows and doors, stick self-adhesive compression seals into the channel where the frame closes. Replace any split or compressed old seals.
3. Fix sliding doors that do not sit tight
   Sliding doors sag over time, leaving a gap at the bottom or sides. Adjust the roller height using the screw on each bottom corner until the door sits flush against the seal when closed. Replace the brush or rubber seal along the bottom track if it is worn flat.
4. Add draft excluders at thresholds
   Fit a draft excluder along the bottom of the door between the conservatory and the house. A weighted fabric excluder works for uneven floors; a brush or rubber strip screwed to the door works for level thresholds.

The joint where the conservatory meets the house is the most common failure point. The sealant cracks as the structure settles, and the gap runs the full width of the room. Reseal it with exterior-grade silicone and check it each autumn.

Add Thermal Blinds or Curtains to Trap a Layer of Air

A layer of fabric or cellular material between the glass and the room slows heat escaping through the glazing. The air trapped in that gap acts as insulation. Close the covering at dusk to hold warmth in overnight, then open it on sunny winter days to let solar heat through.

Honeycomb cellular blinds trap air inside their structure—small pockets run the full height of the blind. Pleated blinds tested in conservatories reduced heat loss by 27 percent. Roller blinds with a thermal backing also work, though the trapped-air layer is thinner.

Blinds are often the better choice in a conservatory. Curtains hung against cold glass trap moisture and encourage mould in the folds, especially in an unheated space. If you prefer curtains, leave a gap at the top and do not let them puddle on the floor—air needs to circulate behind them.

Insulate the Floor or Add Underfloor Heating

Concrete and tile floors act as heat sinks. They absorb warmth from the air and radiate it downward into the ground, leaving the room feeling colder than the thermostat suggests and your feet perpetually chilled.

A thick rug with a dense underlay traps a layer of still air between the cold surface and the room. Wool or high-pile synthetic rugs work well; the underlay matters more than the rug alone. This is the fastest fix for slate, tile or concrete floors and costs under £100 for a conservatory-sized rug.

Underfloor heating changes how a conservatory feels. Electric mats fit under tile or laminate during a floor replacement; water systems require a new screed and suit new builds or major renovations. Both deliver radiant heat that warms surfaces and objects, not just air, so the room feels comfortable at a lower thermostat setting than forced-air heating would need.

Installation means the floor comes up. A professional lays the heating element, adds insulation board beneath it to direct heat upward rather than into the subfloor, then tiles or laminates over the top. The job takes three to five days and disrupts the room completely, but the result is silent, even warmth that offsets heat loss through the glass walls and ceiling.

Electric mats cost less to install than wet systems and work with any boiler. They heat faster but cost more per hour to run. Water systems need boiler capacity—check with a heating engineer before committing—but running costs match your central heating rate.

Choose the Right Heating System After Insulating

Portable electric heaters cost the most to run and solve nothing about heat retention. A 1,500 W fan heater draws as much power as a household kettle and delivers a short-term temperature boost, useful for an hour of evening use but expensive if left on all day.

Set an oil-filled radiator’s thermostat from the start. The idea that you must run it on high first, then switch to the thermostat, wastes electricity. Oil-filled models retain heat after the element clicks off, so they cycle on and off less often than a fan heater and feel steadier, but they still pull 1,500 W when heating.

Extending central heating into the conservatory gives seamless control but requires a boiler capacity check and pipework through walls or under floors. If the boiler is already running near its limit, adding another radiator may leave the whole system lukewarm.

Infrared panels warm surfaces and objects rather than heating the air, so they work well in well-sealed conservatories where convection heaters struggle against cold glass. Mount them on walls or ceilings; they produce no noise and no air movement.

Trench heaters sit low along the conservatory perimeter, often in a recessed channel beneath the glazing. They push warm air upward against the cold glass, reducing the chill zone where most people feel the draft.

Open-plan layouts and hallways distribute heat unevenly. A single heater in a hallway rarely keeps adjoining rooms warm unless doors stay open and air circulates freely. In conservatories with high ceilings, a ceiling fan on low speed pushes warm air back down from the apex where it collects; without it, the floor stays cold while the roof space overheats.

Upgrade Glazing to Double or Triple Glazing with Low-E Coating

Single-pane glass and older double-pane units without low-emissivity coating lose heat fast. A single pane has a U-value around 5.0 W/m²K; modern double glazing with a low-E coating drops that to 1.2 to 1.6 W/m²K. Low-E coating is a microscopically thin metallic layer on the glass that reflects infrared heat back into the room while letting visible light through. The coating makes a bigger difference than the second pane alone.

Triple glazing brings the U-value down to around 0.8 W/m²K, but the jump from good double glazing is smaller than the jump from single to double, and triple costs roughly double. For most conservatories, double glazing with low-E and an argon-filled gap delivers the best return.

A full reglazing runs £3,000 to £8,000 depending on conservatory size and frame condition. At £0.17 per kWh, a well-insulated conservatory used daily might save £200 to £400 a year in heating, giving a payback period of eight to twenty years. Partial upgrades cut that initial cost in half and deliver half to two-thirds of the total heat-loss reduction, making them the practical choice if you plan to move within a decade.

Quick Fixes You Can Do This Weekend

Close thermal curtains or heavy lined curtains at dusk to trap the day’s warmth. The fabric creates a buffer layer between the cold glass and the room, slowing heat loss through the night. If you rent or need results now, this is the fastest return for the money.

• Layer rugs over tile or concrete floors. Add cushions and throws to seating. The textiles absorb and hold a little warmth, and they make cold surfaces feel less harsh.
• Move furniture away from glass walls at night. A sofa against cold glazing loses warmth to the glass; pull it a foot inward and the air gap insulates.
• Run a dehumidifier if condensation appears on windows. Drier air feels warmer at the same temperature, and you reduce mold risk.
• Let the sun in during the day for free solar gain, then close blinds and curtains the moment the sun drops. Even winter sun warms a glass room noticeably.

During a power cut, wear layers of clothing and use down blankets rather than relying on a space heater running on a generator. Close off unused rooms and gather in the smallest warmest space—usually an interior room with one exterior wall. Elderly residents should add a wool hat and thick socks; most body heat escapes through the head and extremities.

Frequently Asked Questions