An extract on #inshot
Forced air heating is probably the type of central heating most commonly installed in North America. It is much less common in Europe, where hydronic heating predominates, especially in the form of hot-water radiators.
Heat is produced via combustion of fuel.
A heat exchanger keeps the combustion byproducts from entering the air stream.
A ribbon style (long with holes), inshot (torch-like), or oil type burner is located in the heat exchanger.
Ignition is provided by an electric spark, standing pilot, or hot surface igniter.
Safety devices ensure that combustion gases and/or unburned fuel do not accumulate in the event of an ignition failure or venting failure.
A simple electric heating element warms the air.
When the thermostat calls for heat, blower and element come on at the same time.
When thermostat is "satisfied", blower and element shut off.
Requires very little maintenance.
Usually more expensive to operate than a natural gas furnace.
Extracts heat from outdoors, either the difficult to install "ground source" or the less expensive "air source" via the refrigeration cycle
Requires less energy than electric resistance heating and possibly more efficient than fossil fuel fired furnaces (gas/oil/coal).
Air source types may not be suitable for cold climates unless used with backup (secondary) source of heat. Newer models may still provide heat when coping with temperatures below 0 C (32 F).
A refrigerant coil is located in the air handler instead of a burner/heat exchanger. System can also be used in cooling, just as any central air-conditioning system.
See Heat pumps
Combines hydronic (hot water) heating with a forced air delivery
Heat is produced via combustion of fuel (gas/propane/oil) in a boiler
A heat exchanger (hydronic coil) is placed in the air handler similar to the refrigerant coil in a Heat Pump system or a Central AC. Copper is often specified in supply and return manifolds and in tube coils.
Heated water is pumped through the heat exchanger then back to the boiler to be reheated