Low Pressure Hot Water Boilers
The State of Michigan classifies a low pressure hot water heating boiler as a boiler which is used for heating the air in a structure and has a maximum operational pressure of no more than 30 PSI. Typically, low pressure hot water heating boilers maintain an operational pressure of between 12 PSI and 15 PSI. There are several categories of low pressure heating boilers which are classified according to the boilers' heat exchanger design. Some common types of low pressure hot water heating boilers are, cast iron sectional, fire tube, and water tube boilers.
Low pressure hot water boilers are by far the most common type of boiler in North America. Low pressure hot water boilers are fantastic devices and offer several advantages over forced air systems. One advantage with hot water heat is it's versatility. Hot water heating systems utilize water as the medium of heat transfer. According to my 12th grade physics professor, there are very few substances on earth that have a thermal capacity even close to that of water. Water is the best medium for heat transfer not only because it is abundant and inexpensive, but also because it is relatively stable and noncorrosive. Thermal capacity is the amount of heat energy in a substance. For example, for water to drop one degree in temperature it must lose approximately 4.2 Joules per gram, while air for example must lose 1 Joule per gram. A good reference website to investigate the specifics of the thermal capacity of substances is: www.engineeringtoolbox.com.
Like water, air has mass (or weight). The mass (or weight) of one cubic foot of air is approximately 0.0807 lbs, while the weight of one cubic foot of water is 62.38 pounds. Pumps in North America are typically rated by gallons per minute or GPM. A typical circulation pump in a home, on a 3/4" copper line, may pump around 8 gallons per minute. Because of practical considerations let us use BTU's as the measurement of choice, since both furnaces and boilers are rated by BTU's / hour. As is typical, if the water from a boiler system enters the circulation loop at 170 F and exits the loop at 150 F, at a rate of 8 gallons per minute, the amount of heat transfer to the space that is being conditioned can be calculated at: (170 F - 150 F) x (8 gallons x 8.34 lbs / gallon of water) x 60 minutes per hour = 80,064 BTU / hour. Now consider that all of this heat is traveling through a 3/4" copper pipe.
Let's do the calculations for a typical forced air heating system. Most equipment manufacturers specify that the ideal static pressure of a ducting system to be used with their equipment should be designed to obtain a static pressure of not more than 0.1" of water column (or "WC). Because 80,064 BTU / Hr. is pretty close to 80,000 BTU / Hr, we will just use the easy number of 80,000 BTU / Hr. Typical furnace manufacturers design their equipment to move about 400 cubic feet per minute (CFM) of air per 12,000 BTU / Hr. when cooling, and 400 CFM of air per 20,000 BTU / Hr. when heating. Given the typical precedence, a furnace capable of heating at a rate of 80,000 BTU / Hr. should move about 1,600 CFM of air or about 96,000 cubic feet per hour (CFH). Not considering turns in the duct work or lengths of duct in excess of 30', a duct properly sized to carry 1600 CFM of air at a static pressure of 0.1" W.C. should be sized at: 17" for round duct or 15" x 15" for square duct. Obviously, the total area of the hydronic (3/4" line) will be 0.442 square inches, while the total area of the duct will be at least 225 square inches. The duct work must have a cross sectional area of at least 509 times more than that of the hydronic piping to transfer the same amount of heat as a hydronic heating system (when comparing a typical hot water heating boiler system to a typical forced air heating system).
Like many people, you may be thinking "a 15" x 15" duct system is not that large". But consider a much larger system, like in a large commercial building. A rule of thumb used by heating and cooling contractors to size heating and cooling systems in homes, is to expect to need about 20,000 BTU / Hr. per 400 square feet (for heating) in a poorly insulated home, and 20,000 BTU / Hr. (for heating) per 600 square feet in a well insulated home. Because commercial structures require considerable amounts of outdoor air be brought into the building, the heating and cooling systems for commercial structures are typically sized at 20,000 BTU / Hr. per 400 square feet for heating, and 12,000 BTU / Hr. per 400 square feet for cooling. Because most new structures are designed with cooling, and nearly every structure built requires some amount of outdoor air be brought into the structure, the installation of some type of ducting system in every new building is a bit of a given. Existing buildings may add air conditioning without meeting the State of Michigan's ventilation requirements by utilizing ductless split systems, however every new structure built in Michigan must meet the State of Michigan's Mechanical Code guidelines for ventilation requirements unless (and this happens very rarely) a variance is given by the local mechanical or building inspector.
So someone might ask, if it is necessary to instal duct work anyway, why would any new building be built with hot water heating boilers? One answer to that question is too allow for easy zoning of certain areas in a building, as detailed on the commercial boilers page of this website. Another reason why hot water heating boilers may be desirable in new commercial facilities and some higher-end residential homes is to provide an extremely even heat by using baseboard heat to apply the heat exactly where the occupants notice the heat loss, at the outside wall of the structure. Utilizing baseboard heating causes a warm curtain of air to move upward along the wall, heating the wall on the inside of the structure. When the inside part of the wall is warm, it radiates more heat, which makes the people near the wall feel warmer because net heat gain due to radiation is higher. Another reason why hot water heating may be desirable in the construction of new structures is because hot water heating may be much more efficient than simply utilizing roof-top unit heating. Today's hot water heating boilers can reach efficiencies up to 96%, while the typical roof-top unit does not even reach 85%, and most are probably in the range of 80% efficiency. Utilizing hydronic heating with a roof-top unit, as back up, is very much common practice in the construction of new commercial facilities. Ice melt boiler systems are another consideration in regards to the design and construction of hydronic heating in new commercial and residential structures. In many cases, it is economical to integrate an Ice melt system into a hydronic heating system because of equipment costs. Often, the same boiler will be used to both heat, and melt snow on concrete. Buildings using water cooled heat pumps use boilers to heat the water that circulates through-out the structure to the water cooled heat pumps. In geothermal systems, boilers may be used as an alternative to very expensive electric heat, in the event that the geothermal system can not keep up with demand.
Determining wether or not to utilize hydronic heat depends on many factors, and operation costs are usually a very important consideration to any engineer or architect who is utilizing a hot water heating system. Johnson Engineering, Inc has the experience and know-how to design economical hot water heating systems, and Johnson Heating and Cooling, LLC has very talented individuals who have installed and worked on hundreds of hot water heating systems. We only do top-notch work, but our customers are happy to find that our rates are always very competitive. Give us a call today, and we would be happy to discuss your situation and come up with the best solution for your needs.
While much of our work is stressful and difficult, at Johnson Heating and Cooling, LLC, our technicians greatly enjoy working on boilers. Boilers are enjoyable for us because we have done so much boiler work that we can do most jobs with very little effort on our parts, although we are always sticklers about working diligently for our customers.. We are very good and proficient with boilers, and our procedures, forms, and experience make the work go smoothly, and cause our customer's boilers to run well. Also, in the heating and cooling industry, if you are not doing boiler work in the winter, you are probably cold. Heating and cooling service men typically go to locations where the heat is off, fix the heater and then leave to go to the next cold location. With boilers, much of the work is done in warm boiler rooms, even when the outdoor air temperatures are sub-zero; typically a boiler room will be around 80 degrees in the winter. So that's a little insight as to the thoughts of an old boiler maker. As of 2013, the 2B boiler maker's license held by David Johnson, the owner of Johnson Heating and Cooling, LLC, allows him to install any size low pressure boiler.
If you live in the State of Michigan and need boiler repair, boiler installation, boiler service, or just a good boiler repair company, give us a call. We have two decades of experience working on boilers and hydronic heating systems, our rates are competitive, and we always treat our customers the way that we would like our families to be treated if they were in your shoes. If you would like to learn more about some of the work that we have done, and look into some of our references that are local to you, just navigate to our contact page and click on the link to your township or city. We have listed a few references from several areas in Macomb and Oakland Counties that are organized under their respective township/city and area codes.
Boiler Service and Maintenance
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