A masonry heater (also called a masonry stove) is a device for warming an interior space through radiant heating, by capturing the heat from periodic burning of fuel (usually wood), and then radiating the heat at a fairly constant temperature for a long period. Masonry heaters covered in tile are called cocklestoves (also tile stoves or ceramic stoves). The technology has existed in different forms, from back into the Neoglacial and Neolithic periods. Archaeological digs have revealed excavations of ancient inhabitants utilizing hot smoke from fires in their subterranean dwellings, to radiate into the living spaces. These early forms have evolved into modern systems.

Evidence found from 5,000 BC of massive blocks of masonry used to retain heat foreshadowed early forms of fire hearths that were used as multifunctional heating sources. Later evolutions came in the Roman hypocaust and Austro-German cocklestove (kachelofen, literally 'tile oven', or steinofen, 'stone oven'), using the smoke and exhaust of a single fire. In Eastern and Northern Europe and North Asia, these stoves evolved in many different forms and names: for example the Russian stove (Russian: Русская печь), the Finnish stove (in Finnish: pystyuuni or kaakeliuuni, 'tile oven', or pönttöuuni, 'bowl oven' for the metal clad version) and the Swedish stove (in Swedish: kakelugn, 'tile stove') associated with Carl Johan Cronstedt. The Chinese developed the same principle into their Kang bed-stove.

A masonry heater is defined by ASTM International as "a vented heating system of predominantly masonry construction having a mass of at least 800 kg (1,760 lb), excluding the chimney and masonry heater base. In particular, a masonry heater is designed specifically to capture and store a substantial portion of the heat energy from a solid fuel fire in the mass of the masonry heater through internal heat exchange flue channels, enable a charge of solid fuel mixed with an adequate amount of air to burn rapidly and more completely at high temperatures in order to reduce emission of unburned hydrocarbons, and be constructed of sufficient mass and surface area such that under normal operating conditions, the external surface temperature of the masonry heater (except in the region immediately surrounding the fuel loading door(s)), does not exceed 110 °C (230 °F)."