Good Ductwork Design Guidelines for New Home or Renovation

Whether you’re excited by plans for a new home or expanding your current Trinity area home to include rooms you’ve long dreamed about, good ductwork design will pay off in comfort and energy efficiency for years to come. The elements of good ductwork design begin as soon as your house plans begin.


The time to incorporate good ductwork design into your new home or addition is while you, the architect and the general contractor are planning the work on paper. A mechanical contractor will design the heating, ventilation and air conditioning (HVAC) system and ductwork, but this work must be integrated into the overall design, not squeezed in as an afterthought. For example, no ductwork should run on exterior walls, nor should it run through untreated airspaces such as a crawlspace or attic.

Measurements by the Bookductwork new house

Your mechanical contractor should follow the Air Conditioning Contractors of America (ACCA) manuals on residential HVAC systems to ensure you receive the right equipment in the most efficient size to adequately heat and cool your Trinity area home or addition.

Manual J helps the contractor calculate the heating and cooling load for each room of your house. This is done by measuring room volume, inputting room use and expected occupancy, orientation (southern-facing rooms get more radiant energy), landscaping and number of windows.

Once heating and cooling load is calculated, the mechanical contractor uses Manual S to select the ideal furnace, air handling and central air conditioning equipment. Ideal means the right size and efficiency for your needs. You may feel bigger is better, but not everything in Texas should be oversized! Many older model furnaces, for example, are energy wasteful due to inefficient design. Repeating that mistake could cost you money, not just by buying too large a new furnace for your home, but by wasting energy every year.

Something Extra?

At this time, work with your mechanical contractor to consider valuable additions, such as:

  • Thick media filter for improved air cleaning
  • Whole-house humidifier
  • Electronic air cleaner
  • Programmable thermostat
  • Zoned heating and cooling
  • UV light inside HVAC equipment to kill germs

These need to be designed while you’re selecting equipment because they may affect blower airflow. For some homes, these are not luxuries. Family members who are very young, very old or who suffer from allergies or respiratory problems will greatly benefit from these thoughtful steps.

Manual D for Ductwork

Manuals J and S lead the contractor to Manual D, for good ductwork design in residential systems. Main ducts and branch ducts are carefully sized to provide ideal airflow to each room. Registers and vents are properly located on walls and ceilings so that return air volume is balanced. A number of possible duct runs may be tried on paper before a final design is agreed upon by both architect and contractor.

Good Ductwork Design Means Comfort

The ideal duct system in your home will be silent, hidden and forgettable. Your family will feel its effects, though, in many ways:

  • Proper ventilation with fresh air
  • Adequate heat in every room all winter
  • Cool, dry air in every room all summer
  • Every room at desired temperature year-round
  • Ideal humidity levels

A Note of Caution

Whatever efficient HVAC system your mechanical contractor and architect have designed on paper, the execution of good ductwork design depends on correct installation.

Some contractors will try to cut corners by following Manual D for the main ducts, but replacing the calculations with standard six-inch flexible ducts for branches. This is bad for you but makes quick work for the contractor. A small powder room may be blasted with gusts of cold or hot air, while a guest bedroom may always feel chilly or damp. Insist on the design you paid for:

  • Mastic sealing all connections
  • Branches sized and installed according to Manual D
  • Ducts tightly attached to house structure, especially at registers and vents, to reduce noise

Don’t let the installing contractor save crew time and materials at your expense. You’ll pay for shortcuts for the life of the system.

Much to Gain

Considering badly designed and leaking ductwork can rob an HVAC system of up to 40 percent of its efficiency, every dollar you invest up front will return to you season after season. Other benefits:

  • Fewer HVAC equipment repair calls
  • Ducts are mostly silent
  • Furnace operates efficiently
  • Central air conditioner works less
  • Ducts stay cleaner

For more help in achieving good ductwork design in your Trinity area home or addition, contact us at W A Air Conditioning.

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June 25, 2014 6:53 pm