Boiler for a heating system

A selectively solid or liquid fuel boiler for a central heating system, said boiler comprising a combustion chamber, means for selectively supplying liquid or solid fuel and combustion supporting gas to said combustion chamber, a heat exchanger for connection to a heating fluid circuit, said heat exchanger including upper and lower headers and a plurality of straight, parallel spaced-apart tubular elements interconnecting said headers for the flow of heating fluid therebetween, said tubular elements being disposed along the back and lateral sides of said combustion chamber, said tubular elements being embedded in refractory material along the major part of their length from their lower ends upward, said refractory material being positioned for direct contact with a burning solid fuel for maximum solid fuel efficiency, interstitial spaces being formed between said tubular elements and the surrounding refractory material to permit uninhibited expansion of said tubular elements with exposed upper parts of said tubular elements being positioned for direct contact with flue gases produced in said combustion chamber for maximum heat transfer efficiency with a liquid fuel.