I popped the kettle on and took a look at the gas meter, to see how fast the dial spins each time I make a cup of tea. The answer is faster than expected!
An interesting thing that I was made aware of recently, is that the natural gas piped into our homes produces a surprising amount of water vapour when it combusts.
With modern boilers, this is not a problem since they are well sealed and vented via flues to the outside. However, where there are gas fires, gas hobs or gas ovens, these might contribute to the total amount of moisture in the house, thus raising the humidity & potential for condensation.