Amanda Langlet and Simon de la Brosse in Erich Rohmer's Pauline à la Plage.
If Alfred Tennyson is to be believed (Locksley Hall, 1835), it's not until spring that "a young man's fancy lightly turns to thoughts of love." But experience suggests that such impulses flourish independent of the seasons. At least they did in my native Australia, where it's mild enough most of the year to make love on top of the bedspread, if not actually outdoors.
Not so in Europe. When, in The Leopard, the Prince of Salina complains that, despite siring six children with her, he's never seen his wife naked above the waist, he echoed a lament familiar to all Europeans. In his case, excessive pudeur was to blame. The rest of us blamed the Arctic temperature of the average northern hemisphere bedroom, which encouraged one to go to bed not only in pajamas, a sweater and bed-socks but a woolly hat, muffler and overcoat as well.
One feels some sympathy for the overseas visitor, and Americans in particular, who is confronted with the manner by which Europeans choose to stay warm or cool. Used to being met, on entering any public building, with, depending on the season, a blast straight from Greenland or a sirocco-like breath of the Sahara, they wonder at the lack of air conditioning in French shops and cafes. It takes some time to accept the prevailing view of what's called climatization - which, briefly summarized, is as follows: if it's too hot for you here, go someplace cool.
Hence the annual exodus from French cities in August and the corresponding invasion of those coastal resorts known as stations balneaires : swimming stations. Most such places don't have air conditioning either, but  houses tend to boast large, shaded rooms and wide verandahs where one can lounge until it comes time to relish the evening breeze off the ocean and perhaps stroll out for an aperitif before a late supper.
Sex in such places is uniformly delicious, a chance to live almost naked and enjoy the sight of others similarly undressed; to shiver as icy condensation is dripped on your naked back from a frosted glass and relish the abrasive brush of starched linen across sun-scorched skin. Not that sex in air-conditioned luxury isn't agreeable - but why accept second-best when experiences so delightfully superior can be had for the cost of a TGV ticket?
Getting warm when it's cold can be more complicated. Well into the nineteen-sixties, heating in most English houses was provided by the electric radiator, consisting of a ceramic rod with wire wound around it. When you switched it on, the wire glowed red hot and a curved metal reflector directed a fitful heat into the room. Some radiators boasted two such rods but snow had to be piling up around the door and wolves howling from the nearby hillside before anyone suggested diffidently "Shall we turn on another bar?" Â
As an on-line history of heating explains (https://www.electricradiatorsdirect.co.uk) "early bar heaters were notorious for having inadequate guards around the hot elements, and many inquisitive fingers came a cropper against its searing temperatures. Fires could be easily started if the heaters were knocked over or if clothes were draped over the grilles to dry." As for their use in bedrooms, where an item of underwear, discarded in the heat of passion, might encounter those red-hot wires, there's nothing like third-degree burns to complicate a relationship.
The fortunate, of course, had open fires, and what Allan Sillitoe in his novel The Loneliness of the Long Distance Runner described, in a nicely evocative image, as "having a chunk of hearth-rug pie", * became even more fashionable after Raymond Radiguet's 1922 best-seller Le Diable au Corps.
Gérard Philipe and Micheline Presle in the 1947 film of Le Diable au Corps.
The novel thinly fictionalized Radiguet's affair at 14 with an older woman whose husband was away at the war. Both felt a delicious frisson in setting alight the kindling with a letter just received from her husband in the trenches of the Somme. Not mentioned were the hazards, ranging from rolling on red-hot embers to wrangling over who should put on an overcoat and fetch a new log from the wood-shed.
In the nineteen-seventies, British Gas launched an advertising campaign. Billboards, superficially enigmatic, showed an ordinary middle-class living room, empty of people. Over the furniture and floor were scattered pieces of both male and female apparel. In the background, an open door, presumably leading to a bedroom, gaped invitingly. No text appeared on the advertisement. None was needed, since goose-pimpled legions drawn from most European nationalities and sexes could supply it for themselves. Install Central Heating, the poster whispered to them, And Fuck in The Warm!
British Gas have just announced a five-fold increase in profits, celebrated by a boost in its rates. They blame the increase on the current political crisis but I suspect that the British, discouraged by Brexit from joining the rest of us Europeans at some Mediterranean or Adriatic resort, are retreating into their semi-detached pebble-dashed suburban castles and enjoying undressing and its related activities indoors.
* Sillitoe also coined the phrase "Nottingham goodnight" to describe how a couple would indulge in an audible but chaste farewell on the doorstep, then, after her parents closed the window and returned to bed, snea into the shelter of the variegated privet.
Agreed. One could also mention the nude male wrestling scene in Ken Russell's SONS AND LOVERS.
There is also a beautifully lit fireside sex scene (or its prelude) in the movie 'Sons & Lovers'.