From the early 1970s onwards sales of cabinet heaters, and with them sales of butane in cylinders, escalated enormously, beginning with Super Ser which rapidly replaced the paraffin heater as the nation's number one choice for spot heating. In a decade, the market for cabinet heaters and the gas they burned grew from nothing to £100 million p.a. This led to increasing demand for storage space, which led to Calor investing in the two largest storage facilities. The first was purchased in 1976: a 30,000 tonne refrigerated storage tank at Felixstowe in Suffolk. The second was a joint venture with Conoco to excavate a vast cavern on South Humberside, capable of containing some 100,000 tonnes of gas supplied from an adjacent sea terminal. This facility, opened in 1985, gave Calor the ability to overcome short-term supply difficulties and to cope with major changes in demand brought on by extremes of weather.