Interest in masonry heaters revived during the energy crisis of the mid-1970s. As people searched for efficient alternative fuel sources, some investigated the European tradition of masonry stoves and began to build them in North America. HEATERS, NOT JUST FIREPLACES The main difference between an open masonry fireplace and a masonry heater is the efficiency of the fire and the amount of pollution released. Another major difference is the path the exhaust follows from the firebox to the chimney. The open fireplace allows the exhaust to vent directly out the chimney. Little of the heat produced is radiated into the room, and the rest goes up the stack. Upon leaving a masonry heater's firebox, hot gases flow through specially designed masonry channels or flues. Ten to thirty feet of flues distribute the heat throughout the mass and keep the exhaust gases within the heater longer, giving more time for heat transfer. HEATERS AND METAL STOVES Masonry heaters and metal stoves have many striking differences: safety, size, weight, method of firing, emissions, and fuel economy. CUSTOM HEATERS Ten years ago, virtually all heaters in North America were custom designed and built with locally available materials. The advantage of such a heater is that it can be designed to suit the builder and the homeowner. MANUFACTURED MODELS In the past 10 years, a number of excellent manufactured masonry heaters have appeared. One company produces Finnish designed soapstone heaters for the North American market.