Boilers and Pumps
The word “boiler” is a bit of a misnomer in most references because they are only heating water, not boiling it. True boilers circulate steam and there is a whole different set of code regulations governing steam boilers versus hot water “boilers”. Without trying to change an accepted description, we shall continue to refer to a heater of water as a boiler. Boilers with a heating capacity as small as 100,000 BTU’s can be found in many homes and can range in size up to millions of BTU’s for large office buildings apartment or condominium buildings and institutions. They all have many things in common such as circulating pumps to drive the water through the pipe system, a heat exchanger to separate the water from the method of heating, a burner or many burners that use a fuel source to raise the water temperature, a method of controlling the temperature of the water like a thermostat and safety devices such as limit controls that prevent the boiler from exceeding the boiling temperature and producing steam. Boilers will have a safety device to release pressure if there is a blockage or failure of other devices.Many larger boiler systems will have a float device called a low water cut-off that will shut down the burners if the water level in the system gets too low. This device would prevent the boiler from going into a melt-down. They will all have a drain for cleaning and a place to release air that “cooks” out of the water when heated. Boilers that are heating water for heating a building of any sort can be made of cast iron or steel for the part of the vessel that holds, stores or transfers the water through the building. These materials cannot be used if the water is to be consumed, used for cooking or bathing (potable needs). Systems requiring potable water require a stainless steel heat exchanger or copper and the piping system would also be copper or the new plastic pipe seen recently. Even the pumps for potable systems have to be constructed of brass, stainless steel or high temperature plastic so not to contaminate the water.
Any boiler that burns a fuel such as natural gas, propane, fuel oil or even coal requires a chimney to exhaust the products of combustion. The type of chimney would be specified by the manufacturer and the gas / oil codes and could be masonary, stainless steel, double walled metal or even a specific type of plastic vent material. If there is a defect in the chimney the occupants of a building are in danger as the exhaust gases are extremely toxic. Many of the boiler systems using black iron piping for the circulatory system of the water will incorporate a filter system and chemical feeder to eliminate the harmful buildup of mineral scale and sludge in the pipe system that restricts the flow of water and results in wasted energy. The chemicals that are periodically added to the system are supplied and installed by a water treatment company and not your HVAC contractor.
Boilers that are used for heating recirculate the same water over and over whereas boilers that supply domestic water needs for cooking and bathing have fresh water entering the system to replace the water that is used. The recirculated systems are referred to as “closed loop” and the systems that allow release of water at taps and faucets are “open”. When water is heated it expands and generates pressure in the system. To prevent bursting the pipework there has to be a method of controlling the expansion. This is accomplished by installing a tank with a cushion of air inside that will compress as the water expands, hence the name “cushion tank”. This tank is above the elevation of the boiler and commonly has a visual glass gauge to indicate the level of the water in the tank.
All boilers have a method of filling or adding water to the system that is connected to the municipal water pipe system. The pressure of the municipal water is much higher than the pressure in the boiler system and would cause the boiler pressure relief to open and release the over pressure. To prevent this, a regulator is added to the water supply line to reduce the pressure of the incoming water so that there is sufficient pressure to overcome the pressure in the boiler, but less than the safety relief control. As part of this same regulator there will be a device that prevents the backflow of water into the municipal system should the pressure in the boiler exceed that of the regulator.
Boilers are becoming quite trendy in the residential market again with people wanting in-floor heating anywhere they have ceramic or marble tile floor coverings such as bathrooms or kitchens. Wood flooring can also have radiant heating underneath. I personally find foot comfort for a lot less cost by putting down a bathmat or area rug that I can replace for pennies when I get tired of the colour. I don’t see the point of heating the floors in the summer to 80 degrees F. when the air conditioner is trying to cool the house to 73. Those that can afford the energy costs will have what they wish, but for me, good pair of socks from Wallmart or a comfortable pair of slippers does the trick.