What is the internal energy of an ideal gas at room tempature?

Is it energy efficient to shut heat registers in areas that aren't being used?

• A family member strongly believes that closing the heat registers of rooms/areas that aren't being used is the best way to save on gas bills in the winter. I can almost agree if the room that isn't used can be closed. But what about common areas like the kitchen/dining room/living room? Is it really efficient to close the register in the kitchen and open the one in the dining room only, just because we are in the dining room and not the kitchen? These areas do not have doors and cannot be closed off. Even the bathroom register is closed when "not being used", yet the door is left open. The furnace runs and I feel cold. Where is the heat going? Is this really energy efficient?

• Answer:

  DO NOT CLOSE ANY REGISTERS!. Doing so is very waste full. Your system was at one point designed to run at a certain capacity with all of the registers open. When you start to close registers, you loss that spaces ability to provide a certain amount of air (measured in CFM) required by your system to operate at its peak efficiency. IE A 2 ton unit requires 800 nominal CFM to operate effectively. Approximate CFM requirement per room for a 2BR, 2 bath, kitchen, dining and living are : each BR (165*2), living(200), Dining(75), Kit(100), bath(65*2)=835 CFM. By closing the kitchen and bathrooms you lost 230 of required CFM to run your system efficiently. Those 230 CFM are required to return the cooler air to be reheated. Here's the kicker YOUR system WILL NOT reduce or adjust it's power consumption. SO your are paying to heat 600 CFM at the 835CFM price. YOUR system I believe is running longer than it should and working harder(higher Amps= more $) to meet the heating and cooling needs.