• What devices do we use to heat buildings and what fuels do they use?

two big sources of building heat r the people in it & the machines & lighting in it. Often, even in ''cold'' northern states & Canadian provinces, factories need almost no added heat. When they do need heat, the most common things to do r heat water (or use steam) & pipe it around, or burn natural gas (like in many if not most homes). Electricity is seldom a good thing to use - usually electricity is made by making steam, that is used to turn a turbine, so why make heat from electricity? In some places, geothermal heat sources r available & used. There is also a lot of passive solar heat - the sun shining down on a black roof puts a lot of heat into buildings. During the day, getting rid of heat is often a bigger concern!

Almost all wasted heat is due to poor ventilation balance - too much ''fresh'' air going that needs to be heated, & if the pressure is too high (from too much air going in), then it ''blows'' out the doors, around windows, & even through cracks in the walls. The best way to conserve heat to properly balance & maintain the ventilation, & use the other building sources (like bodies & machines & lights) in the design (but it might get cold at night when the building is unoccupied). Sometimes it is cost effective to recover ''waste'' heat & store it for when it is needed, but surprisingly, that is pretty rare to be cost effective. Some is wasted due to inadequate or poorly maintained insulation, too.

To heat the building, it might be good to keep some equipment on even when it is not needed.