ILLUSTRATION NY Times Style Magazine Multiple Choice Popular Mechanics Homeowners Clinic Popular Mechanics Dear Darpa... Popular Mechanics Tankless Water Heater Popular Mechanics Tracking Tractors Popular Mechanics Tunnel Vision   June 2005. Illustration for Popular Mechanics Magazine. An illustration showing the inner workings of a tankless water heater. Tankless water heaters are typically used to retro fit plumbing without existing hot water supplies.