I went to school for HVAC/R, but we never covered this question that's been bugging me ever since. Does your gas furnace heat your hot water heater, or are they separate? Is the hot water heated by electric? Is a gas furnace the same as a boiler? Confused.

Answers by question marks--1-Could but usually separate, 2-Could be electric or by gas, solar, geothermal and others, 3-No but some units use water to heat air.

From a layperson's view, in simple terms, leaving out the rare ones:
A furnace heats air for vents.
A boiler heats water for radiators or baseboard.
Hot water can be tankless off the boiler, tankless from an 'on demand' separate unit, or heated in a hot water heater tank. (Oil, gas, electric, etc for any of them)