SZL double drum water tube steam boiler is horizontal type water tube boiler, the combustion equipment is chain grate. The boiler adopts fast assembly or packaged assembly structure, boiler with steam capacity lower than 4t/h is fast assembly water tube structure, boiler with steam capacity between 6~25t/h is consisted of upper part (boiler heated part) and lower part (combustion equipment). The wood fired hot water boiler has the advantages of compact structure, high steam quality, sufficient output, operate convenient and environmental protection.