Furnaces, other than for experimental purposes; protective grids, being parts of a hot-air space heating apparatus; spark protective plates and base plates for furnaces; chimney flues; hot-air space heating apparatus for solid, liquid or gaseous fuels, namely, wood, paperboard, ethanol, spirit, butane and propane; radiators; heat accumulators; heat exchangers not being parts of machines; water heaters; heating installations for water; humidifiers for furnaces and central heating radiators; el...