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Gas Boiler Heating

Basics of Gas Boiler Heaters

Today's gas boiler heaters turn a small amount of water into pressurized steam which can heat your house through radiant tubing under the floor or through the classic stand alone upright house radiators. Gas boilers must have an adequate supply of natural gas or propane fed to the internal burners. Then the steam exiting the boiler must be kept at a constant pressure, usually 12 psi. In addition, there must be adequate ventilation present in the boiler room to allow full burning of the fuel. Also, adequate exhaust conduit must also be provided to the outside so that carbon monoxide does not build up in the boiler room. Local building codes are in space in most municipalities governing the operating parameters of the gas boiler. So seek qualified professional help before attempting to install one yourself.

Gas Boiler
Gas Boiler

Gas Boiler Components

There are several components built inside as well as outside the gas boiler that are all very important to its proper functionality.

Gas Boiler Internal Components

  • Aquastat

    An aquastat regulates the water temperature inside the gas boiler. It is an efficiency device that saves gas by not firing until the water temperature falls below a high limit set point. It is located inside the gas boiler cabinet and works in coordination with your wall thermostat.

    Gas Boiler Aquastat
    Gas Boiler Aquastat

  • Water Pump

    An internal water pump moves water into the boiler.

  • Gas Valve

    A gas valve controls gas going into the boiler burner chamber. The valve is controlled by the thermostat and aquastat.

  • Tridicator Gauge

    This internal meter shows boiler water temperature and pressure. The gauge can used to monitor proper operation of the boiler's burner shut off temperature to assure the aquastat and other control devices in the boiler. Water pressure can be measured in pounds per square inch (PSI) and H2O feet. Temperature can be seen in F or C.

    Gas Boiler Tridicator
    Gas Boiler Tridicator

  • Pressure Relief Valve

    If the pressure inside the boiler rises above a certain level, say 30 PSI, an external pressure relief valve releases excess water out of the system.

  • Burners

    One or more gas tubes, called burners are in the combustion chamber for the gas. The fire should be nice and blue. Some red and yellow is okay, but excessive amounts of reds may indicate extra carbon monoxide (CO) being produced. The cause of too much CO may be too much gas being pumped in or impurities in the gas such as dust particles around the boiler.

    Gas Boiler Burner
    Gas Boiler Burner Fire Should be Nice and Blue

  • Pressure Relief Valve

  • Boiler

    The kettle that holds the water to be heated inside the boiler cabinet.

  • Internal Heat Exchanger

    This is the area between the burners and the boiler tank. Boiler heat exchangers may get plugged with carbon build up, dirt, or dust, thus reducing the efficiency of the boiler. After powering down the boiler, the debris can be cleaned out with a brush.

    Gas Boiler Heat Exchanger
    Gas Boiler Typical Heat Exchanger

  • Flue Gas Collector

    This 5-sided galvanized steel box collects exhaust from the burners and funnels it to an outlet pipe, which goes outside.

    Gas Boiler Flue Gas Collector
    Gas Boiler Flue Gas Collector

Gas Boiler External Components

  • Zone Controller Valves

    These valves connected to the home feeder pipe from the boiler allow you to direct heat to certain areas in the home. For example, first and second floors can have separate control valves. These valves are controlled by individual thermostats.

    Gas Boiler Zone Control Valves
    Gas Boiler Zone Control Valves

  • External Pressure Regular Expansion Tank

    This tank is split internally inside by a bladder or diaphragm. Above the diaphragm is water from the boiler. Below the diaphragm is air. Since water is not compressible the tank allows the volume of water to expand so that pressure does not build up in the loop. There is a Shrader air valve (similar to a bicycle valve) on the bottom of the tank that can manually release or inject air in the tank. You can test for diaphragm ruptures by releasing a small amount of air from the tank. If water comes out, then the diaphragm has a tear.

    Gas Boiler Pressure Regulator
    Gas Boiler Pressure Regulator

  • Air Scoop and Auto Air Vent

    This device mounted above the external pressure regulator purges air bubbles from the hot water line coming from the boiler. Removing oxygen air bubbles reduces corrosion in the piping. The auto air vent has a small vent cap on top that should be left loose. This allows trapped air to be released from the air scoop.

  • House Pressure Reducer

    This device reduces and regulates the water coming out of the boiler to a constant level. One one side of the pressure reducer is house tap water, which may be above 60 PSI. ON the other side is boiler circulating water, which is much lower, around 12 PSI. Keeping the boiler system water low improves efficiency by taking full affect of the heat exchanger in the boiler.

    Gas Boiler External Pressure Reducer
    Gas Boiler External Pressure Reducer

The Hot Water Cycle of Gas Boilers

The water pump continuously cycles water through the boiler and radiators around the home. It sends hot water to the radiators, which transfers the heat into the living space, leaving, cooler water to be returned to the boiler. The cooler water returning to the boiler will eventually bring it down to a lower set point, which triggers the burners to fire. The burners will bring the boiler temperature back to a set high point, turn off, and then not turn on again until boiler temperature has fallen back down to the low set point.

Uses for Gas Boiler Heaters

Gas boilers are used to heat homes. However, they can do it in a number of ways. Some boilers feed hot liquid or steam to visible radiators in the living space. Some output to tubes under the floor, called hydronic radiation, which allow the heat to raise uniformly into the living space. If hydronic floor radiation is used the floor must be well insulated above the craw space or basement.

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