Cows do not have 4 stomachs. They have a single stomach that is divided into 4 sections that have odd digestive functions. The rumen breaks down the lawn that the cow eats. The next digestive phase occurs in the reticulum where the cud is produced. The cud gets burped back into the cow’s mouth where more chewing occurs. Then, the chewed cud is re-swallowed into the omasum that detachs excess water from the food massâ€¦ Next is the abomasum where the food is finally digested. In a way, that delicious steak that the people I was with and I savor is nothing more than lawn that has been processed into beef by the steer. Bovine digestion is just a single example of how everything in life is a process; Using that same vein of thinking, even the air the people I was with and I breathe in our homes and workplaces undergoes a process with HVAC systems. The air does not change as dramatically as our lawn into beef example, but before it’s heated by the oil furnace or cooled by HVAC cooling tubes, that air is first processed by the air filter, then depending on the MERV rating, air filters detach particulate matter from the air between 0.3 and 10 microns. The higher-rated HEPA filters are capable of capturing bacteria and microscopic allergens. Ironically, the purpose of HVAC filters is not to scrub the air for your benefit. Their purpose is to keep the particulates from entering the inner toilings of the HVAC where it can accumulate and affect the efficiency of the unit, but protecting your HVAC program is the real reason why it is important to change the HVAC filters typically. Healthy air to breathe is simply a side benefit that the filters and HVAC systems make possible, just savor beef and milk made by cows.