Different types of ductwork installation methods are used based on the heating/cooling system and design layout. Safety standards must be met for gas-air furnace systems, and electrical HVAC systems must have no leaks and a balance between supply and extract air. Extended plenum and radial piping designs are common, with new designs for hot, humid climates using ductwork running inside the house.
There are several methods of installing ductwork driven by the types of heating/cooling systems in homes and design layouts. Ducting patterns are extended plenum, radiant ducting, or a combination of these. Some run through a ceiling instead of an attic, and others run through a crawl space or basement, but all designs have their basis in the placement of the furnace. Many locations have energy efficiency codes and duct installations must meet these standards. New duct materials changed some methods, and experimental prototypes for hot/humid climate home construction led to further innovations over the old proven duct installation plans.
Ducting systems for gas-air furnaces are specific to safety issues when using gas. For safety reasons, all components and duct connections for a gas-air furnace system must meet the performance temperature values as well as the smoke development and flame spread values. Some residential and light commercial buildings have duct installation projects with the ductwork outside the building. Indoor installations only require insulating enclosures, but outdoor installations also require the application of weather and water resistant sealant.
There are standards for installing electrical central heating, ventilation, and air conditioning (HVAC) systems. These duct installations must have no leaks and a balance between supply air and extract air. There should be no loss of airflow velocity due to crimping, improper sizing, or bending too close to extended plenums. Long ranch-style house designs and those with vaulted ceilings on one end of the house are best suited for extended plenum duct installations. Even two-story houses need an extended plenum design to reach the upper rooms.
Standard installations for central plant with extended plenum design are for three different furnace types: upflow furnaces in closets or basements, downflow furnaces in mobile homes or narrow crawl spaces, and horizontal furnaces which may be used in attics and some crawl spaces. From the orthogonal extension of the plenum of the oven, branches of round tube branch off and protrude from each side to feed the registers of the individual rooms. The return air is received via another main line with identical branches from the rooms to the HVAC to be reconditioned. Instead of rigid round pipe for extended plenum branches, some duct installation projects use flexible tubing.
Ductwork for radial piping designs do not have extended plenums, but have round pipes connected directly to the furnace plenum and separate individual routes to the drains and log outlets. These can only be efficient if the oven is centrally located. These radial duct designs are the easiest to install and the cheapest because there are fewer ducts to lose air velocity and efficiency. Additionally, there are semi-rigid flexible pipes that can be run individually to each room and are claimed to diffuse noise pollution into the home. Additionally, these semi-rigid hoses have been tested and proven to provide better air quality over time by pulling moist air out in humid climates and preventing dust from settling and trapping mould.
A new type of duct installation design was tested and found to be a dramatic improvement over any other duct installation design for use in hot, humid climates. Making use of specific calculations, these designs make use of ductwork running inside the house below the ceiling plane at a much lower cost and produce zero energy homes. There can be no duct losses to the outside and favorable gains/losses are eliminated because there is no heat build-up in an attic for the ducts to deal with, so set point temperatures remain nearly constant in the ducts. These designs also use transoms in each room to promote good airflow to the returns.
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