I am about to install a new radiator in my apartment; we removed the old one without noting the direction of water flow. So I now have two pipes sticking out of the floor and I don't know which is which. The pipes are now capped.
The new radiator is marked for the direction of flow; through the valve and in at the top of the radiator. Will it make much difference if the new radiator is connected backwards, water going in at the bottom and the valve after the radiator? And if it is important, how do I establish the direction without flooding my apartment?