When two people get on like a house on fire, they hit it off at once and become firm friends almost on first meeting. It describes an instant, lively rapport rather than a friendship that builds slowly, and it is nearly always said warmly, as praise for how easily two people click.
The simile has also been used more broadly, outside friendship altogether, simply to mean doing something very quickly and with great force or intensity. That older, wider sense of rapid, vigorous action sits behind the narrower modern use about people, where the speed and intensity of a house fire are transferred to the speed and intensity with which a friendship takes hold.
What’s the origin of the phrase ‘get on like a house on fire’?
The image at the root of the phrase is straightforward: a house fire takes hold and spreads with alarming speed, consuming a building far faster than anyone would expect. Wiktionary’s etymology note describes the phrase as a metaphor reflecting the popular idea that house fires are archetypally fast and fierce once they get going. That same notion lies behind the related variant ‘like a house afire’, which dictionaries explain by pointing to the building materials involved: houses made of timber or thatch, such as the log cabins built by American pioneers, burn very quickly once alight, which is why the comparison carries such force.
Applied first to any rapid, energetic action and only later narrowed to describe people hitting it off, the phrase seems to have shifted its target over time from the speed of an event to the speed of a friendship, while keeping the same underlying image of something catching and spreading fast. One idiom site claims the expression dates back to at least the early 19th century, with similar wording appearing in British literature and journalism of the period, but this claim comes from an uncorroborated source and should be treated with caution rather than taken as settled fact. What can be said with more confidence is that the comparison trades on something universally recognised, the sheer speed of fire taking hold of a house, and that this is what gives the phrase its warmth when used of two people who simply click.