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Hydronic distribution and ducted heat distribution are two of the most common types of heating systems. Both type has its own advantages, and either one may come out on top in a given situation. Each system, of course, comes with unique advantages and disadvantages, making a choice somewhat complex. This article reviews the effiency of hydronic heat vs. ducted heat and lists out some of the pros and cons of each.
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What is Hydronic Distribution?
For those who are wondering, hydronic heat distribution is a type of heating system which uses hot water as a working fluid. Either steam or liquid water may be used, depending on the system. Hydronic heating is not a new technology - in fact, many older heating systems rely on hydronic heating. In these systems, steam passes through radiators, which transfer heat to the surrounding air and condense the steam back into liquid form. Oddly enough, the primary form of heat transfer from radiators is convection, not radiation. Though this type of system is rarely used today, some older homes do still use steam radiator systems.
Modern hydronic heating systems typically use heated water rather than steam. These systems may use radiators or baseboard heating, in which the heating pipes pass heat directly into the floor. The advantage of using liquid water is that either hot or cold water may be used, which allows systems to double at heating and cooling.
Image: Wikimedia - Radiant Floor Circuit Collectors
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Hydronic Distribution Efficiency
There is, unfortunately, very little data on the efficiency of hydronic distribution systems. The efficiency of a given system varies according to the piping used, the type of heat conduction used (baseboard radiant, radiators, and so on), pumping requirements, and so on. Additional pumps or fans will contribute to lowered efficiency.
It does seem, however, that hydronic heating systems may have higher thermal efficiencies than typical ducted heat systems. According to Home Energy Magazine, a hydronic radiative heating system in a typical home of 1500 ft2 with carpeting has a thermal efficiency of about 90%. A forced air heating system, on the other hand, could have thermal efficiency below 50% during blowing. The overall efficiency of a heating system will depend on a number of factors, such as leakiness of the home and heating ducts, fan efficiency, andfurnace or other heating source efficiency.
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Advantages and Disadvantages of Hydronic Distribution Systems
One major advantage of hydronic heating systems is that they can be easily built into new energy-efficient homes. Efficiency can be increased by increasing the thermal mass of floor systems. Hydronic radiative systems may also be quieter than ducted heating, since there is no fan or blowing air. There may also be benefits to air quality, since heating ducts can develop mold and dust issues. Because water is an excellent conductor and relatively dense, hydronic systems require much less working fluid. This means that hydronic heating systems take up less room than ducted heating systems.
Some systems even allow differential room heating, in which residents can change the heat in any given room. This feature, of course, comes at a cost premium.
In well-designed systems, hydronic heating may be substantially more efficient than ducted heating. However, there is little data on this issue. It does seem likely that hydronic heating would be less power-intensive than other systems, as it doesn't rely extensively on fans. However, some systems may have a large pumping requirement, which reduces efficiency.
There are some disadvantages of hydronic systems. In the event of a retrofit, it may be probitively expensive to install a hydronic system. In addition, hydronic systems can typically only provide heat. This means that a separate AC system is required, increasing expense and space requirements. However, some homes may combine heating and cooling into a single hydronic system using a chiller boiler. This can be expensive, however.
One note: it is a misconception that hydronic heating systems prevent air dryness. They do not dry the air any more or less than a heating duct system.