Air conditioning for conservatories

Why conservatories are hard to keep comfortable

A conservatory is mostly glass, and glass lets in a lot of solar heat and loses heat quickly once the sun goes. That's why the same room can be too hot to sit in on a June afternoon and too cold on a February evening. Many conservatories end up as storage for half the year for that reason.

A wall-mounted split air conditioner deals with both problems. It is an air-to-air heat pump, so it cools in summer and heats in winter from the same indoor unit. It also has its own thermostat and remote, which matters for building regulations, as explained below.

Leeds isn't a hot city by average figures. The Met Office 1991 to 2020 averages for Leeds Weather Centre give a mean daily maximum of 21.4°C in July and 21.0°C in August. A south-facing glass room can still get far hotter than the outdoor air on a sunny day, since the sun heats the inside and the glass keeps the heat in.

Building regulations and the independent heating rule

The Planning Portal says conservatories are normally exempt from building regulations when they are at ground level, under 30 square metres, single storey, separated from the house by external quality walls, doors or windows, and have an independent heating system with separate temperature and on/off controls.

That last point is the one that matters here. Extending the house's central heating into the conservatory, without separate controls, can take it out of the exemption. A split air conditioner with its own thermostat and on/off controls is a separate system, which is one reason it suits conservatories.

Two related points. Taking out the doors between the house and the conservatory, or making a new structural opening, needs building regulations approval even if the conservatory itself is exempt. And the electrical supply for the unit must be done to the building regulations, which is normally handled by a registered electrician who self-certifies the work.

Sizing a unit for a glass room

For ordinary rooms, Daikin's UK sizing guide gives a rule of thumb of about 0.1kW of cooling per square metre at a 2.4m ceiling, and adds 10% to 20% for large south or west facing windows. A conservatory is almost all window, so treat that rule as the lowest possible figure, not the answer.

Worked example: a conservatory on a semi in Horsforth. It measures 3.5m by 3m, so the floor area is 3.5 x 3 = 10.5 square metres. The basic rule gives 10.5 x 0.1 = 1.05kW. Adding the full 20% for large windows gives 1.05 x 1.2 = 1.26kW. Its pitched roof means the average height is above 2.4m, which Daikin says adds capacity in proportion to the extra volume. This is still a room where the walls and roof are glass, and the rule assumes an ordinary room with a few windows. The real figure depends on the orientation, whether the roof is glass or polycarbonate, any blinds, and the glazing type, so it should come from the installer's heat-gain and heat-loss calculation.

Ask the installer to show you that calculation. A unit that is too small will run flat out on sunny afternoons and still not keep up. One that is too large will cycle on and off and do a poorer job of removing humidity.

What to look at before you buy

A unit won't fix every problem on its own. Some simple changes make the room easier to cool and heat, and they can mean a smaller unit.

• Roof type: a polycarbonate or older glass roof gains and loses far more heat than a modern insulated roof.
• Blinds: roof and side blinds cut solar gain before it reaches the room.
• Orientation: a south or west facing conservatory needs more cooling than one facing north or east.
• Draughts: gaps around old doors and frames waste heating and cooling.
• Use: a room used every evening needs a different approach from one used at weekends.

Where the indoor and outdoor units go

The indoor unit needs a solid wall, which in most conservatories means the house wall, or the dwarf wall if there is space. High-wall units are the usual choice. Where the only solid wall is low, a floor-standing console unit can be an alternative, since it sits at skirting height. Ask the installer which suits your layout.

The outdoor unit usually goes on the ground or a bracket close by, which keeps the pipe run short. Under permitted development in England, the outdoor unit must be 1.5 cubic metres or smaller, meet a 37 dB(A) noise limit at the neighbour's nearest habitable room window, and in a conservation area can't go on a wall or roof facing a road. Most conservatories are at the back of the house, which helps in a conservation area.

On a semi or terrace, which make up most Leeds conservatories, the neighbour's window is usually close. MCS 020 a) is the method used to check the 37 dB(A) limit, taking the unit's sound power, the distance and any barrier such as a solid fence. Our noise guide shows how it works.

Questions to ask at the survey

A good survey for a conservatory takes longer than one for a bedroom, because there are more variables. Ask the installer how they calculated the capacity, and whether they allowed for the roof type and the direction the glass faces. Ask where the indoor unit will go and which way the air will blow, since a unit aimed at a sofa or dining table can feel draughty.

Ask how the condensate will drain. In cooling mode the unit takes water out of the air, and that water needs a route to a drain or a soakaway. In a conservatory with a dwarf wall, the drain can often run straight outside.

Finally, ask for the outdoor unit's sound power level and the 37 dB(A) calculation for your nearest neighbour's window, in writing. If it fails, the installer should suggest a different position or a barrier, and shouldn't carry on regardless.

Running costs, summer and winter

Because it is a heat pump, the unit gives out more heat than the electricity it uses. Its heating efficiency is shown as SCOP, and Daikin's guide calls a SCOP above 3.5 high performance.

Worked example for heating: say the conservatory needs an assumed 1.5kW of heat for 4 hours on a winter evening. That is 1.5 x 4 = 6kWh of heat. With a SCOP of 4.0, the unit uses 6 / 4 = 1.5kWh of electricity. At the Ofgem price cap for October to December 2026, electricity is 26.32p per kWh by Direct Debit, so the evening costs 1.5 x 26.32p = 39.5p. A plug-in electric heater gives out the same as it uses, so 6kWh would cost 6 x 26.32p = £1.58.

In summer, cost depends on how hot the room gets and for how long. Check the rated cooling power input on the data sheet and multiply by the hours you expect to run it. Our running costs guide has more examples.

Leeds and West Yorkshire conservatories

Conservatories are common on the semis and detached houses built across Leeds suburbs such as Horsforth, Alwoodley, Garforth and Rothwell, and in towns like Wetherby. Many date from the 1990s and 2000s, when polycarbonate roofs were common, and these are often the hardest to keep at a steady temperature.

Leeds has 80 conservation areas. If your home is in one, the outdoor unit can't go on a wall facing a road under permitted development, but a rear conservatory normally avoids that problem. If the house is listed, talk to the council before any work.

VAT, grants and installers

Installing an air-to-air heat pump in a home is zero-rated for VAT until 31 March 2027 under HMRC's VAT Notice 708/6. Our partner installers are MCS certified and apply the 0% rate on domestic installations.

The Boiler Upgrade Scheme has offered £2,500 towards air-to-air heat pumps since 28 April 2026, but only where the system replaces fossil fuel heating, is MCS certified, and the home has a low carbon hot water system. A unit added to a conservatory alongside a gas boiler normally won't qualify.

Anyone handling the refrigerant must hold an F-gas certificate. Ask to see it.

Sources

• Planning Portal, Conservatories and building regulations
• Daikin UK, Air conditioner size guide
• GPDO 2015, Schedule 2 Part 14 Class G
• Ofgem, Energy price cap unit rates
• HMRC, VAT Notice 708/6
• Met Office, UK climate averages (1991 to 2020)
• MCS 020 a) Air source heat pump sound calculation
• Leeds City Council, Conservation areas
• GOV.UK, Apply for the Boiler Upgrade Scheme
• GOV.UK, F gas in refrigeration and air conditioning