本来故宫在冬天是选用地炕火道来采暖的。

Originally, the Imperial Palace in winter to use with fire heating.

用金属管做的（如铁管）叫做电热床或炕（地炕）。

The electric heating bed is made of metal pipes (such as iron pipes).

故宫的采暖方法以地炕火道为主，以炉火为辅。

Heating method of the the Imperial Palace is pit fire, with the fire auxiliary.

结合地炕采暖，可燃气费用与用薪材、秸秆采暖费用相当。

If heating with the Ground Kang, gas expense was similar to that of firewood and maize stalk.