Firewoods vs coal in Banished

In Banished it is possible to use firewoods to warm the residents of the houses. But also coal.

If you test the efficiency of these energy resources, then you will see that coal costs much more. Indeed, if the same number of people is to be warmed up, it will take 4 to 5 times more labors to fill the mines and extract the necessary quantity of coal.

Thus coal has much less efficiency, it is a trap with a chasm of time and energy.