It is quite common to see a floor register in homes located in colder climates. In newer homes the floor registers are usually dedicated to heat lines. Using floor registers for heat lines is preferable when possible because heat rises, making them more effective.
In older homes floor registers may also be used for air conditioning lines. This is especially true if it is on a second story or there is a basement. Many older homes which have central air were retrofitted with central air. Running the duct work up through the floor and using a floor register is often preferable to tearing up walls to install wall registers.
Positioning Floor Registers
When installing floor registers it is best to stay close to the perimeter of the house. This will help to keep the register out of the general path of foot traffic. Use a floor register made out a durable material such as cast aluminum, brass, or brushed nickel. Moving a register involves making another cut in the floor and moving the duct work, so positioning should be done once if possible.