Identifying Heating Systems

When describing the heating systems in a building, there are a number of variables to consider, including:

• The type of fuel used.
• The medium used for heating (air, water, steam).
• Open vs. closed flame.
• Direct vs. indirect fired.
• Convection vs. radiant.

Fuel Type

The most common fuels used are natural gas, oil, and electricity. In the greater Toronto area, natural gas is by far the most popular, because it is the least expensive. When determining the type of fuel used in a system, here are a few points to consider:

• Gas-fired systems will always have gas piping (typically black steel) leading to the fixture. Although not required, most people paint this pipe yellow for identification. Gas meters, usually located outside the building, also suggest gas heat.
• For oil fired systems, an oil tank in the building is an obvious indication of this type of fuel. Oil tanks which are buried outside the building are less obvious but can be identified by the presence of an oil fill and vent line outside or a small, black rectangular fuel gauge inside the main boiler room. There are obviously environmental implications associated with buried oil tanks.
• Electric systems are harder to identify, unless we are talking about electric baseboard heaters (don't mistake hot water convectors for electric baseboards). Electric heating systems may consist of heaters located in the ductwork for the HVAC system. These are not readily apparent.
• If the building is heated by package roof top units, these can be gas or electrically heated. The presence or absence of gas lines above the roof can tell you which it is.
• Heat pumps use electricity for the compressor; however, a gas fired boiler may be providing hot water to the heat pump or, if the heat pump is an air source, electric duct heaters may provide backup heat.

Heat Distribution Medium

To differentiate between forced air and hot water or steam is usually straightforward. Forced air systems use ductwork, and hot water or steam systems use pipes and radiators, convectors or fan coil units.

Some systems use hot water or steam and forced air: a boiler generates hot water or steam, which is pumped through pipes to a fan coil unit. The fan blows air across the hot coil and warm air is delivered to the space. There may or may not be a duct system.

Hot Water and Steam

To differentiate between hot water and steam is more difficult. One clue is to look at the piping going to the radiators. In some old steam systems there is only one pipe. This pipe brings steam to the radiator and also returns condensate back to the boiler. A single pipe system is definitely steam, but a two pipe system could be either.

A second way is to look at the pipe which is leaving the bottom of the radiator. If there is a small round fitting connected to the pipe, this is an indication of a steam system (it is actually a steam trap). The steam trap only allows condensate to return to the boiler.

Open vs. Closed Flame

These types of heating systems are typically natural gas or oil fired. With an open flame system you can see the flame. The air in the building can come in contact with the flame. It has to as the building provides combustion air. A closed flame system does not allow the air within the building to interact with the flame.

Open flame systems are by far the most common. These would include most types of interior furnaces, boilers, or unit heaters. Closed flame systems are those which use outside air for combustion and do not draw air from within the building. These would include certain types of high efficiency furnaces, boilers, gas-fired radiant heaters, and all roof top package units.

The circumstances where closed flamed systems would be required typically involve buildings which contain explosive dust or vapours. For example, some types of wood working or wood manufacturing plants would require closed flame systems because of the amount of sawdust generated inside.

Direct vs. Indirect Fired

Most heating systems are indirect fired. This means that the products of combustion are vented to the building exterior and do not enter into the building. Any heating system with a chimney is an indirect system.

There are however, direct fired systems, where the products of combustion are delivered inside the building. Common examples of direct fired heating systems include facilities where there are large volumes of air being exhausted, due to processes, such as kitchens with large exhaust fans.

Because there is so much air being exhausted from these buildings, there is a requirement for air to be brought back in. Direct fired units typically bring outside air into the building, after heating the air with an open flame. Since there is such a large volume of air being exhausted, there is little risk of carbon monoxide or carbon dioxide build up in the building.

There are special requirements for direct fired heating systems. For example, the heated air brought into the building cannot exceed the capacity of the exhaust system by more than 10%. Direct fired heating systems have to be interlocked so that they can only work if the exhaust system is functioning.

Convection vs. Radiant Heat

Convection or forced air systems heat the air within the building and blow the air around to heat the space. Radiant heating systems work in a similar fashion to the sun (on a much smaller scale, obviously!). Objects in the building are heated by electromagnetic waves. Radiant heating systems can be embedded in the floor or ceiling (electric or hot water radiant heat), or can be suspended from the ceiling (electric or gas-fired infrared radiant heaters).

Forced air systems with ducts have certain advantages including the opportunity to provide:

• cooling
• air filtration
• humidification
• fresh air into the building

The advantages of the radiant heating systems include:

• Even Temperature Distribution
  Since the radiant heaters are directed downward or embedded in the floor, the floor slab tends to get warm and there is a more even temperature over the height of the building.

• Lower Heating Bills
  Since the people and objects in the building are warmed directly, the actual air temperature is somewhat lower (65F vs. 70F) and, therefore, there is less heat loss from the building.

There are generally three intensities of infrared radiant heating systems. Most systems are typically low intensity. This means the source temperature would be below 1200F. High intensity systems have source temperatures as high as 5000F.