A High Velocity System (or SDHV for Small Duct High Velocity) is a style of heating system that uses a boiler and small-diameter flexible ductwork to heat the home. It’s a (relatively) recent development in air delivery that tends to be found in larger, newer homes.
What is an SDHV Heating System?
SDHV works like this: A high efficiency boiler heats water that is circulated through a hydronic heat transfer coil, and a continuously running variable-speed fan blows air over this coil to heat the house. It’s called high velocity because the fan is very powerful and the air travels faster through the smaller ducts, but the main principle of the system is not really based on air speed, but rather air pressure.
Typically there is a central 6” trunk line with 2” take-offs branching out to tiny circular vents. The plenum duct is kept continuously pressurized, and the air flows out to areas of lower pressure throughout the house. This maintains a gentle air circulation, keeping temperatures evenly distributed.
SDHV Benefits– Small and Efficient!
These systems provide numerous benefits, most notably a smaller footprint. Not only is the heating unit itself smaller than a conventional furnace, but a high-velocity system also does away with the large main stem of ductwork, using a main duct just six or eight inches wide. The smaller branch ducts can be run through tighter spaces, and the small, round vents can be located in the floor, ceiling, or walls.
A high-velocity system can also deliver better energy efficiency, potentially more even heating, constant air filtration, and better safety.
One misconception is about noise. Some people assume these systems are noisier than conventional forced air systems, but if that’s the case, it’s usually due to kinked tubing, or an insufficient number of outlets. With proper setup, the air flow can be balanced for quieter operation. A well-designed and tuned SDHV system will actually run much quieter than conventional furnaces. The quality of the ductwork is critical in this regard; it must be well insulated, airtight, and run in a smooth path.
Some are also concerned about uneven heating. If you’re experiencing hot and cold spots in a house with a high-velocity system, it’s most likely due to having too few vents and/or poorly insulated, leaky ductwork. As with any other kind of high-efficiency system, expert design and installation are key to the best performance.
You need to do a few things annually with these systems to keep them working their best. The hydronic coil inside can get choked with dust, causing the blower motor to work too hard. If air conditioning is connected to your high velocity system, there will be a second coil (called the “A-coil”) that also must be kept clean. The blower motors, boiler, and electronic control system should also be checked and tested annually.
Instant Plumbing offers a High-Velocity System cleaning and inspection package. Give us a call, and we’ll help you maximize the life and efficiency of your heating system.