The ancient Greeks were undoubtedly clever and many of their inventions are still in use today (in some form or other). They were the first to use radiant central heat. This is how it worked: Homes and buildings were built with "under-floors". Beneath their floors they would keep fires lit to generate heat and that heat would also be circulated around the villa through the clay pipes in the walls. This practice was the primary way to heat dwellings- along with burning wood- through the 1700s. The Chinese also used similar methods of heating their homes called "baked floors".
In December 1919 (a hundred years ago!), Alice patented her furnace which supplied central heat for entire buildings and residences. This system was much safer than burning wood in the home. The difference between her invention and other furnaces of the time was that her furnace did not require stoking. It had air ducts to spread the heat through the building. It included multiple burners and ran on natural gas. What's even more notable is that Alice was able to patent her invention as an African American woman long before the Civil Rights and Women's Liberation Movements!
Your thermostat is the center of your home's heating system. It is a switch that is, simply, sensitive to temperatures. Most thermostats today are digital and use electronic controls to sense temperature changes. Most can be programmed to customize the temperatures in the house. If your thermostat is placed too close to a heating source (such as direct sunlight or a table full of candles), it will skew the thermostats' temperature gauge. This will cause the heat to turn on and off erratically. Be sure to remove all heat sources from the area surrounding your thermostat.
If you smell gas inside your house, get everyone out of the house immediately. Leave the door open. Once you are safely away from the building, call 911 or the gas company. Some people cannot smell a gas leak's rotten egg odor, but there are other signs of a leak such as a hissing sounds, white mist or fog, and dead vegetation/plants in one area. The hissing noise near your HVAC could be a bad compressor, leaking refrigerant line, or leaky valve.