A gas pack is a heating and cooling system within one unit. Air conditioning powered by electricity and a heat pump powered by natural gas, propane or oil are housed in a single box. Most gas packs are used in commercial buildings rather than residential ones.
There are many advantages to using a gas pack for heating and cooling. Perhaps most importantly that they are powerful and efficient. They are especially useful for heating or cooling multiple rooms or a very large space.
Gas packs themselves do not take up a lot of space. They are also comparatively easy to repair since all the components are in one place.