Those things were everywhere in the Netherlands when I was a child - 70's. I had one above the sink in the kitchen in my student apartment (half of a pigsty converted to human habitation, pigs in the other half, a thin wall in between - that's what you get when studying at an agricultural university and living on a farm) running off a propane tank in the garden. We had one in the kitchen and a bigger one in the bathroom, running off natural gas which the country had plenty of after the discovery of a large gas deposit in the northern Netherlands. There were no vents to the outside, the things just vented into the room. They're called 'geisers' (geysers) in Dutch.