North heat load index 1 m2, power 50 watts. A heating period 150 days, total heat: 50* 150 days *24 hours *3600 seconds =648000 kj.

The calorific value of 1 kg standard coal is 29307 kj.

Quantity of standard coal: 648,000/29,307 = 22.11kg, equivalent to 45 kg of ordinary coal.

If the boiler efficiency is 50%, the coal consumption is 45 * 2 = 90kg.

A heating period 150 days requires ordinary coal (calorific value of 3,500 kcal/kg): 30,000 square meters *90 kg = 2,700 tons.

Daily coal consumption: 2700/ 150= 18 tons.