HVAC systems that regulate temperature and air quality to keep enclosed areas warm in wintertime typically depend on natural gas combustion to sustain boilers, pumps, radiators, meters, and other components. The burning gas heats air or water for circulation around the enclosed space. Gas and liquid flow must be controlled and metered accurately using various sensing and modulating elements such as flow control valves or isolation valves — also known as shut-off valves — or both.