Hay Boxes, or Fireless Cookers, were in wide use by the late nineteenth and early twentieth centuries (and probably much earlier), as a means for saving on fuel costs (whether wood, coal, or some form of gas). They are simple, low-energy slow cookers that, according to some accounts, date back to biblical times. Food would be heated up in a pot on a conventional stove for a few minutes and then put into an insulated box or compartment to cook for a few hours. The simplest ones were simply boxes full of hay, cloth or other insulating material and these were commonly home-made devices. However, many of the stoves built ca. 1900 had fireless cooking compartment built into them, and there were also a wide variety of them available for sale as separate units. There use was so common, in fact, that special cookbooks were written for this method of cooking, because cooking times had to be adjusted for them.
This is the diagram of a fireless cooker
that was submitted with a patent in 1911.