If you have an oil tank which you have to fill, there’s your clue you use oil to heat your space.

No oil tank, but a black pipe connected to your boiler or furnace? Likely gas. The picture is of a water heater, but you get the idea.

Electric baseboards or perhaps hot air made by a heat pump.

A furnace heats air which is delivered to your space through ducts and registers. This is forced hot air heat.

Hydro-air is a hybrid system in which a boiler heats water which is sent through coils in air handling units. Air passing over the coils is heated and sent through the ducts and registers.

A boiler is a vessel in which water is heated and sent through pipes to the heat emitters in the space. The water can stay as a liquid or be heated until it forms steam. Either way, it’s a boiler and you have what is called hydronic heat (hydro for water).

Steam boilers have gauge glasses which allow you to see where the water line is in the boiler. If you have a gauge glass, you have steam.

Hot water boilers have expansion tanks. They provide room in the system for water to get bigger as it gets hotter

Hot water systems can be either forced or gravity (this is extra credit stuff). Very old gravity systems, which were put in before electricity, were designed to move by virtue of the differing densities of hot and cold water. They have no pumps. They will have large pipes in the basement and radiators for heat emitters. Some former gravity systems have now been adapted with pumps to become forced systems. More modern forced hot water systems have pumps and smaller pipes.

Hot air and hydro air systems will have registers.

Hydronic systems may have radiators, fin tube baseboard, convectors, fan coil units including kickspace heaters, or radiant floors, walls or ceilings.

 

Steam radiators will have steam air vents  or steam traps.

If you have just one pipe attached to your radiator, it is most probably a steam radiator.

If your radiator has a connection only on the bottom of all its sections, it is a steam-only radiator. See how there is a “pipe” through the bottom, but only spacers at the top?

 

Hot water needs to be able to make a circle through the radiator so hot water radiators have a connection through the top of all the sections, like this. Steam can use this radiator as well, so check for steam vent or steam trap for positive identification.

Hot water radiators have air vents like this. Note the vent is at the top of the radiator, where the air in a hot water system collects. Steam vents should be in the middle of the radiator.

  

Standing pilot systems have thermocouples which sense the pilot flame. The gas valve will have a thin copper tube or silver, braided wire which runs into the firing chamber of the boiler, and the top dial on the gas valve will show the words “on”, “off” and “pilot”.

 

   

• Intermittent ignition systems will only show “on” and “off” on the gas valve. They have systems which light the pilot each time the boiler has to fire. This version uses a spark to light the pilot gas. The orange rubber coated spark wire is the clue.

 

Milivolt– These older systems generate their own power- enough to operate the safeties, thermostat and gas valve via the pilot flame. Needless to say, they are all standing pilot systems. Instead of a thin copper tube, the gas valves will have a silver, braided cable attached to the top terminals of the gas valve.

120 volt– Pre-war systems may have 120 volt controls, and also often have mechanical safety devices with mercury in them. Oil fired equipment may have 120 volt controls as well.