Here in Korea winter is finally coming. Just yesterday I had to heat my house for the first time this season. Korean homes are heated by what I think is a rather unique heating system called 'Ondol' heating. Here is what wikipedia has to say about it::
The main components of the traditional Ondol are a firebox or stove (agungi; 아궁이) accessible from an adjoining (typically kitchen or master bedroom) room, a raised masonry floor underlain by horizontal smoke passages, and a vertical, freestanding chimney on the opposite exterior providing a draft. The heated floor is supported by stone piers or baffles to distribute the smoke, covered by stone slabs, clay and an impervious layer such as oiled paper.
As interesting as this sounds, my heating system is nothing like that. In fact the only thing it has in common is the floor is heated. My 'Ondol' and I believe most modern Ondol heating systems are hot water heated.
The way it works is there is a centralized hot water heater, and since its Korea, it is usually a rather fancy computerized machine. Pictured below is my hot water heaters central control panel. All i know is in the center there is a bigger power button and a smaller 'reset' button, in case it crashes. How does a hot water heater crash? I have no idea, but mine crashes a lot, though I do know its over due for a replacement as its quite old.

Next to the hot water heater are the valves that turn on and off a number of closed circuit water pipes running through the floor of the house.

Each closed circuit pipe circulates the water through the floor in different parts of the house. Basically a simple way to think of it is as a giant hot water radiator under your floor, the shape of the pipes under the floor is very much the same as well.
This brings me to something I have been thinking about recently. In Korea a common practice if you want to save on your heating bill when you are not using part of your house is to close some of the hot water valves, thus cutting of heat to those rooms. On the TV news a few weeks ago they reported that this practice doesn't actually reduce your heating bill, because the water pressure is just increased in your other pipes, the same amount of water is still rushing through the open pipes, just with more pressure. I however I am not entirely sure this is true.
Bare with my thermodynamics ignorance here as I explain the problem and my thinking to you. So if the pressure is increased it means the water will circulate through the open pipes quicker. Which means the water will cool off less as it circulates around the house and back to the heater. Which means the heater needs to do less work to heat it up again before sending it back into the house. However this is where i could be wrong, because isn't the point of the hot water to lose heat? The more heat lost by the water means the warmer your house, but maybe less efficient? Hmmm, I am confused, so lets look at it another way. Imagine the floor heater as a giant heat sink. The bigger the heat sink the faster it cools right? So if you close some of the valves it will cool slower as the heat sink will be smaller, which mainly means your house will heat faster with more valves open and slower with less. Is it more efficient though? Another factor here though, is if some of your rooms are cold, then your warm rooms will lose heat to the cool ones as most people have no insulation between their rooms.
Anyway my conclusion is this is a rather complex problem, that probably only has an answer on an individual house basis, depending on your house layout, size and heating system. Anyone have an answer to this? Since the hot water heater is computer controlled, wouldn't this be a great thing for it to regulate and control. You select which rooms you want to heat, the computer figures out how to do it efficiently. Either way though I am a big fan of the Ondol heating system. Its quiet, clean, and totally hidden. Best of all you always have warm toasty feet, which is especially nice in the early morning.