A UK home with an external air conditioning unit. Paul Briden/ShutterstockThe recent heatwaves mean that many people in northern Europe are now looking at new ways to cool their homes. Historically, northern European building design has prioritised heating, but more home owners are considering adding air conditioning.While 88% of US homes have air conditioning, only about 3% of UK homes have it. What are the big issues?Fitting an air-conditioning system to an existing home is likely to cost more than £6,000 for a whole house. It will also mean running pipework through walls, which may require renovation afterwards. Running costs range from a few hundred pounds to a few thousand per year depending on the size of the UK property. It is worth remembering that electricity in the UK is twice the cost of the US, where more homes have air conditioning.Typically, to fit air conditioning you have an outdoor unit (the condenser) and a fan unit mounted on the wall or in the ceiling, connected by pipes. These pipes feed cold water from the condenser into the fan unit, which cools the air (which can be reversed in winter to provide heating). This is known as a split system. Then there’s planning and consent. Condensers generate noise and can be unsightly. You generally don’t need planning permission if units are discreetly located. But this is difficult to do with flats, as the units create noise which may disturb nearby properties. Planning consent is likely to be required, so it’s worth checking. Air conditioning must also comply with various building regulations, for instance those related to safety.Adding to historic homesAnother factor is the age and construction of the existing home. Historic buildings have thick stone walls and a large thermal mass, so they take longer to cool down or heat up. Often, they are deliberately designed to be airy and well ventilated, as this helps control problems like high humidity. However, this means a higher rate of air leakage, so air conditioning units have to work harder. Plus those high ceilings means a larger air volume to cool. Installation may also require special planning permission and may be more complex and expensive. Recent heatwaves have driven up demand for air conditioning in France. It is also worth considering the levels of humidity. This may rise depending on the air conditioning system used, and could be a particular problem in historic buildings. When air temperature drops, as happens if you cool it, the humidity inside a room increases. This may mean a dehumidifier is needed.Another air conditioning option is to use portable units. These combine everything in a single machine. However, they are only intended to cool small spaces and would tend to be less energy efficient, with higher running costs. They also need a duct to dump the heat, which typically means fitting a vent to an outside wall or window. Sticking the pipe out of an open window will let the heat in and the chilled air escape. Installing US-style window units may require a chat with a planning department first to check on restrictions. These also need windows that open vertically (such as sash windows), which isn’t typical in many modern UK homes.When shopping for air conditioning, much like “miracle” heater scams, also be wary of similar scams regarding “miracle” coolers at cheap prices.Environmental consequencesEnvironmental impact has long been another concern. Historically air conditioning used ozone-eating CFCs as a refrigerant, but these are no longer used in units on sale today. Air conditioners still do contribute to the urban heat island effect, which makes cities hotter, as the heat from the building is released via the condenser into the surrounding air. This heat island effect is likely to be a factor in making heatwaves worse. Carbon emissions will vary, depending on the source of electricity. In France or Portugal, where the grid is nearly all carbon neutral (nuclear, hydro, solar or wind), emissions would be low. But they’d be much higher in Poland or Cyprus, for instance, which use relatively few renewables and limited or no nuclear sources in their national electricity mixes.Other options?Given that heat pumps are increasingly standard in new UK homes, configuring them to also provide cooling in the summer could become the way forward. Most existing UK systems are not set up to do this, but more are likely to go on sale if demand rises. Read more: Older people are more vulnerable in heatwaves. Here’s why – and how to stay safe Another option that will save on your energy bills is to try to cope with summer heat using what is called passive cooling, by adding awnings, external shutters or shading your windows. These are definitely the lowest cost options and can be easiest to install, and should bring the temperature down. This is traditionally how buildings were kept cool in summer.Heatwaves are part of the cost of climate change. And while weighing up the ways to cope with it, it’s also vital to think about how our choices could also escalate the continuing extreme weather, particularly given that it will affect older and more vulnerable people more adversely.Dylan Ryan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.