Hydronic Heating Systems Mandan ND
West Fargo, ND
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Keeping Your Whole House in Hot Water
On a cold winter's night, nothing is nicer than a cozy, warm house. If you live in an area of the country that calls for home heating for the better part of three seasons, then hydronic heating can be a very comfortable choice for a new heating system. Yet many people in the United States are not familiar with hydronic heating because, as yet, it still only commands a small percentage of the overall domestic home-heating market. But the market for hydronic heating is warming up, and with good reason. Hydronic heating uses hot water or, in older systems, steam to distribute heat through baseboard convectors, free-standing radiators, or in-floor radiant coils. It is an option worth exploring for both new and older homes, because when properly installed, it is energy efficient, clean, quiet and draft-free.
Hydronic heating is already quite popular in some areas of the country. It is the predominant heating system in New England, New York, New Jersey, and Pennsylvania and a popular choice in Wisconsin, Minnesota, Northern California, the Pacific Northwest, and the Rockies. Farther south, where the heating season is shorter and there is greater demand for air conditioning, homeowners more often install HVAC (heating, ventilating and air conditioning) systems that run heating and cooling in one duct-based system. There are four primary components of a hydronic heating system: the boiler, the piping, the heat emitters (usually baseboard convectors running along the outside perimeter of a room, or radiant piping circuits installed in floors or ceilings), and the controls. When you use baseboards, you are heating the room through natural convection. When you use old-style hot-water or steam radiators or newer in-floor tubing, you are heating using both thermal radiation and convection. Baseboards heat the air, which in turn makes you feel warmer. In-floor tubing, commonly called radiant flooring, heats the furnishings and room surfaces in the room, as well as the occupants, so you can keep the thermostat lower and still feel warm. Because components for convective heating and radiant heating work together (with baseboard convectors costing less to install than radiant tubing, though radiant floor heating is somewhat more efficient than baseboard heating), designers can combine the two types of hydronic heating to meet most any need and budget. Furthermore, hydronic heating has the ability to reach out and handle loads that go far beyond space heating, often without increasing the size of the boiler. For example, hydronic heating can be used for domestic water heating, heating of spa or pool water, and snowmelt on a walkway or driveway. In a snowmelt system - effectively a radiant floor system operating outdoors - automatic snow and ice detectors sense the presence of precipitation and the outdoor temperature. If the temperature falls below 36° F, for example, and the detector detects precipitation, that combination of events activates the heat. Priorities for all these tasks can be handled automatically by the control system.
Why It Works Hydronic heating capitalizes on a couple of scientific facts: 1) water is a very good storer and transporter of heat, and 2) heat always flows from a warm surface to a cold surface. Natural convection relies on movement of air resulting from the difference in temperature between cold air and warm air. Cold air, which is denser and heavier, enters the bottom of a baseboard convector and rises as it is heated. As it rises, it cools, becomes denser, and falls toward the floor. The temperature difference between floor and ceiling can vary by a few degrees, less than half the difference experienced with forced-air heating. You don't feel a difference in the heat, head to toe. In contrast, radiant floor heating heats the objects in a room as well as the room air. It heats much like the sun heats, in line of sight. Since your furnishings, walls, floor and your body are all warmed by the radiant heat, you radiate less body heat toward these surfaces, losing less heat yourself, and therefore feeling comfortable, even in a cooler room. Unlike forced-air heating, radiant heat keeps the floor warmer than the ceiling, warming your coolest body parts first. Hydronics vs. Forced-Air Heating When you heat a room hydronically, you may feel more comfortable than you would in a room heated by forced air, which creates drafts and may noticeably dry out the air. Forced-air systems are nosier than hydronic heating and can more readily spread dirt and germs harbored in the ducts whenever the air is circulating, notes Steve Gribbin, marketing service manager at Slant/Fin Corp., a baseboard heating and boiler manufacturer. And because air is a far less efficient conductor of heat than water, a forced-air system requires large ducts - which can present design constraints - to equal the heat transported by the 3/4-inch tubing typical of many baseboard systems. Also, forced-air systems can create positive air pressure, sending heated air out through cracks around windows and doors, says John Siegenthaler, professional engineer, a consulting engineer specializing in hydronic system design. Siegenthaler also points out that when ducts are used both for cooling and heating, duct placement compromises the efficiency of both tasks. For the most efficient heating, the ducts should be near the floor; for the most efficient air conditioning, the ducts should be near the ceiling. "A system capable of dual operation is, necessarily, a compromise," he says.
IMPROVING COMPONENTS Baseboard Convectors Baseboard heating is a low-mass, fast-response system that will warm a room faster than a high-mass, slower-to-respond radiant system. So baseboards are a good choice for rooms that you want to heat up quickly. Baseboard heating also responds faster when you want to lower the temperature in a room. High-mass radiant flooring, however, will lose only a few degrees when the heat is turned down, keeping the room relatively warm for those who prefer it that way. Baseboard heating is cheaper to install than radiant floor heating and is easier to install than either radiant flooring or forced-air systems in retrofits - usually without requiring any major teardowns - or in additions. Baseboards are typically placed below windows. The rising warm air creates an upward current of air just inside the window, countering the downdraft of cool air from the windows. Furthermore, the effectiveness of baseboard heating is not compromised by floor covering, such as thick rugs and padding or by placing most types of furniture in front of the radiators, points out John Woodworth, retired technical director of the Hydronics Institute, an industry trade association. Several manufacturers offer baseboard convectors. While they all operate on the same principles, individual piping products may have different attributes. For example, Slant/Fin Fine/Line 30 baseboard uses double-bent aluminum fins that, according to the manufacturer, achieve extra heating surface in a slimmer enclosure, while the edges of each fin are wedged against each other to stop vibrations. The baseboards incorporate no-noise expansion cradles that eliminate metal-to-metal contact, the company notes. For bathrooms, kitchens, basements and other high-moisture areas, the company also markets Fine/Line 30RR baseboard, which is made with rust-inhibiting materials throughout that resist the rusting effects of moisture, salty air and laundry chemicals.
Easier Piping Piping for convection heating has come a long way over the years. Older baseboard systems were generally all piped with 1/2-, 5/8-, 3/4- or 1-inch copper tubing that was rigid and labor intensive to cut to size and often required several elbows to connect each radiator. (Brass flexible connectors, for reducing the number of fittings, have been available for baseboard installation for over 40 years, but have never been very popular.) Though copper tubing is still a very popular choice, today's convection systems increasingly use a flexible plastic tubing, generically called pex (cross-linked polyethylene) and the more rigid but still flexible plastic pipe, pex-al-pex (aluminum tubing sandwiched between two layers of polyethylene). These products install very quickly and enable installers to put into place a system without any joints between the boiler and the convectors. The pex tubing is corrosion resistant and can be installed directly into concrete, soil and the framing of wall floors and joists, says Tibor Kovac, product manager of heating at Ipex, a manufacturer of plastic tubing and piping systems. The tubing is typically 3/4-inch-diameter, but it can range anywhere from 3/8 to 1 inch in diameter. And, because pex and pex-al-pex install quickly, it is relatively easy to run separate loops to each room for individual zoning, so you can save on fuel by not heating unused rooms or by heating rooms only to the comfort level needed for each space.
Controls The most dramatic improvements in hydronic heating systems have been in the controls, which now go way past simple setback thermostats, incorporating features that enable fine tuning for energy savings and operating diversity. Several companies, including Honeywell, Tekmar and Caleffi North America, offer controls that can coordinate multiple loads, such as space heating, snow melting, pool and spa heating, and domestic hot water, prioritizing among tasks as needed. Controls for integrated hydronic systems could be labeled multi-load multi-temperature, because each type (baseboard, radiant, domestic hot water, snow melting, pool and spa heating) is a different load, and each system uses water at a different temperature from the same boiler. These controls can manage all those loads simultaneously by assigning priorities, shifting loads, and regulating water temperature. For example, domestic hot water (at sink, shower and tub taps) is generally given first priority, while heating the spa might carry a low priority. Once the higher-priority loads are satisfied, the controls can redirect heat output into the lower-priority loads.
Outdoor Reset Control In traditional, older style hydronic heating, the boiler maintained a constant water temperature (usually at 180° F), regardless of the outside air temperature. When a thermostat called for heat, it sent a signal to the zone valve to open, and the circulator pumped the heated water through the baseboard radiators in that zone. But for a good part of the heating season, water need not be heated to the maximum setting in order to heat a room for comfort. On warmer days, it is possible to heat rooms to a comfortable temperature with cooler water by adding an outdoor reset control that regulates the water temperature of the boiler based on the temperature outside, saving energy and reducing boiler cycle time. The reason this saves energy is that a warm boiler loses heat up the flue continuously, and the warmer the boiler, the greater the loss. The heat loss during the period the boiler is not actually firing is called the standby loss. Standby loss is the reason the seasonal efficiency (annual fuel utilization efficiency, or AFUE) is smaller than the firing efficiency. Outdoor reset controls thus increase the boiler's AFUE. The Honeywell AQ475A Aquatrol Outdoor Temperature Compensator, for example, incorporates a temperature compensator installed at the boiler and two temperature sensors, one placed outdoors that reads the outdoor temperature and another at the boiler that monitors the water temperature of the supply water to the home. "The compensator adjusts the water temperature of the boiler according to the outdoor temperature, so that you heat your room enough to compensate for heat loss to the cold outdoors," explains Ron Jamieson, market manager for Hydronic Systems at Honeywell. The service technician sets the control for the coldest actual winter temperature and the boiler maximum temperature, and the unit automatically calculates the appropriate water-temperature range. By adding room thermostats to the mix, it is possible to further refine control of the heat, based on changing temperatures within each room. (A crowded room or a room with a lot of lights on warms up more than an empty, dimly lit room.) The thermostat can override the outside reset control and turn down heat when appropriate.
Boilers The most important factor to look for in a boiler is energy efficiency. Boiler efficiency is based on venting and the type of venting material used. The U.S. government mandates that new boilers meet a minimum efficiency of 80 percent. Boilers at 85 percent efficiency and over are widely available. Various manufacturers add features that make their boilers user friendly and/or energy efficient. For example, the Weil-McLain GV Series 3 gas boiler with a direct vent operates at 87 percent efficiency and comes with a built-in outdoor reset control with priority for domestic hot water using an indirect-fired water heater. The unit, which vents directly outside, either through a wall, the roof or an unused chimney, incorporates sealed-combustion technology that uses outside air for combustion. This feature, notes Bob Mandigo, senior product manager at Weil-McLain, also reduces energy usage - and fuel bills - by reducing air infiltration. Keeping combustion byproducts out of the house eliminates problems caused by indoor air contaminants. The Slant/Fin Concept 21 sealed-combustion gas boiler also uses a two-pipe system vented to the outside. Featuring a variable-input burner, the unit, which operates at 85 to 85.6 percent efficiency, depending on the model, can adjust the fuel and air mixture to continuously provide optimal combustion as the air intake varies due to wind, ice, accidental damage, or blocking of the chimney or vent terminal. The boiler also includes a gas-input rate-adjustment feature that, during installation, enables the heating contractor to adjust the boiler's "size" to match the homeowner's actual heating requirements, conserving energy while retaining the ability to readjust the input rate should heating requirements change.
What About Air Conditioning? Homeowners can use hydronic heating and also install central air conditioning, either in the traditional way with a full-size duct system, or more innovatively, with a mini-split system, sometimes called ductless air conditioning. A third option is installing high-velocity air conditioning that uses very small, 2-inch-diameter, flexible ducts that can be routed through a 2-by-4-inch partition. The cooled air is slowed down at the room diffuser to an airflow rate comfortable for room occupants. Make of Hydronics What You Will Hydronic heating systems offer a great deal of versatility. "You can design a hydronic system specifically for the needs of any home," Siegenthaler points out. "Rather than having to shoehorn a given heating design into a home, home heating designers can fashion a system that takes into account the whole picture - everything from window layout and planned floor coverings to anticipated setback schedules and whether or not a spa or pool is anticipated for later installation. This ability to do everything with one heat source is a major strength of hydronics, compared to forced air." n William and Patti Feldman are a husband-and-wife freelance team based in New York.