ACCA Manual D Duct Design (3rd Edition)

The residential duct system is designed to match the heating and cooling equipment blower capacity.  The Manual D duct layout provides the contractor with a "duct blueprint".

How to accurately design HVAC duct based on ACCA Manual D

  • Undersized residential HVAC duct makes the temperature rise through the furnace too high
  • Undersized duct systems impacts cooling capacity by freezing the coil
  • Proper residential duct design software ensures that the needed amount of conditioned air is delivered to each room
  • Undersized heating and cooling ductwork results in unacceptable noise levels
  • Oversized furnace and A/C duct will result in too low velocity and rooms not receiving adequate comfort
  • Calculate properly the available static pressure (ASP) - Information on blower and all air side pressure drops for the coil, air filters, registers and grilles
  • Calculate total effective length (TEL) - This is the longest supply path + the longest return path + fittings
  • Calculate friction rate value based on available static pressure - per ACCA Manual D the friction rate must be more than 0.06 and less than 0.18 (0.06-0.18 FR)
  • Design adequate return air paths for all rooms
  • Size duct based on needed CFM and friction rate for each room
  • Verify duct air flow rates and velocities are within ACCA Manual D recommendations
  • Provide residential air distribution system layout with duct sizes
  • Provide correct locations of HVAC returns (regarding high or low position)

ACCA Manual T Air Distribution (1st Edition)

Properly sized grilles and registers are essential to proper room comfort.  You can have a properly sized HVAC system, proper equipment selection and a properly sized duct system but improperly sized grilles and registers could ruin all that hard work.

How to accurately size HVAC registers and grilles with ACCA Manual T:

  • Verify register and grille face velocities
  • Verify supply grille throw and spread (direction of jet)
  • Verify pressure drop produced by terminal devices (grilles and registers)

Avoid having Goldilocks ductwork.  Confirm your HVAC duct designer uses ACCA approved residential Manual D duct sizing software and theory to size your duct work.  You are investing a lot of hard earned $$$ - with proper heat loss/heat gain results (Manual J), you can select a properly sized system (Manual S), and proper duct sizing (Manual D).  Then your Comfort System will be Just Right

Why Should You Insist on a Proper Residential HVAC Duct Design?

Like everything, there is a right way and a wrong way.  Many contractors use improper duct sizing techniques because they want to save materials, time and labor.  Their shortcuts result in a spider web of duct work of varying sizes and lengths.  Supply registers deliver inconsistent comfort and the returns are often undersized.  Do you really believe all your rooms are receiving the required CFMs consistently?

If not installed properly you can expect your comfort system to be ineffective.  Your system may be properly sized using ACCA certified Manual J load calculation results, and you may have selected a great HVAC unit, but your poor residential duct design will result in HVAC ducts that don't deliver the required airflow to each room.  Or sometimes contractors will add an addition onto an existing system and the new heating and cooling system is too small to cover both the existing space and the new addition.

Some symptoms of a poor duct work design are:

  • Your air conditioner runs continuously
  • Your energy bills seem unusually high
  • Some rooms may seem very cold while others seem very hot
  • Your air filter never needs to be changed and always looks new
  • Occupants seem to have a higher than average incidents of sore throats and respiratory issues

Many municipalities and permit offices are requiring an residential ACCA certified Manual D duct design along with a Manual J load analysis and Manual S HVAC equipment sizing to meet code requirements.  These residential HVAC duct designs accurately size the duct work needed for your properly sized heating and cooling system.

Some things to look for in a good home HVAC duct design are:

  • Supply trunks that are equal distances apart (spread out evenly along the supply plenum).  This provides even heating and cooling distribution and ensures each room maintains about the same temperature.
  • Correct number of registers, correct diameter of supply trunk.  Too many supply ducts and the CFMs will be too low delivering too little comfort to each room.  Too few supply ducts and the CFMs will be too high delivering too much comfort to each room.  Improper duct sizes will distort the flow to each room.  For example, if a bedroom has too small a supply branch while the bath's is too large, the bedroom will hardly get any air while the bath will get far too much.

Improperly sized return trucks:

  • Coil could freeze up if undersized
  • Compressor is forced to overwork
  • House will take much longer to achieve the desired comfort level

When your home duct system is properly designed, air will distribute evenly throughout your home.  Each duct will carry the proper amounts of CFMs.  Save yourself money, time and aggravation.  Invest in an ACCA Manual J load calculation and Manual S equipment sizing to ensure you select the properly sized HVAC unit and an ACCA Manual D duct design and enjoy years of comfort.  Your home will no longer be a Goldilocks home - instead it will be Just Right!

Watch our What is ACCA Manual D YouTube Video

What is Manual d duct design?

ACCA Manual D Residential Duct Designs - the 3rd step in the quality hvac design process

Developed by Hank Rutkowski

Need to hire a  Manual D designer?  So you are getting ready to replace an old HVAC system or perhaps you are building your dream home.  Before making that purchase or even selecting the installing contractor, there are 3 important factors to ensure optimum comfort in your home for many years to come.  This webpage addresses the 3rd step - sizing HVAC supply & return duct properly using ACCA Manual D duct sizing developed by Hank Rutkowski.

Why do Energy Star, LEED and many permit offices insist on Manual D duct sizing for your supply and return duct work?  Because Manual D Residential Duct Systems has a proven track record over many decades just like the Manual J & Manual S.  If your HVAC designer uses proper duct sizing techniques:

  • Layout of your home
  • Room X Room heating and cooling needs based on your Manual J load calculations results.  This ensures the correct heating and cooling is supplied resulting in the desired temperature
  • Appropriate register sizes based on Manual T air distribution
  • Proper supply and return main plenum size based on velocity and friction rate.  Too high a velocity will produce noise issues.  Some contractors use the same size branch duct to all rooms while the bath needs very little conditioning and the Great Room requires 2-3 times as much

Manual D residential ductwork sizing is the third important step in achieving a proper, quality

HVAC installation for optimum performance.  If the duct work (air distribution system)

is improperly installed, each room will get varying amounts of comfort and can result in

great discomfort and disappointment in your New Comfort System.

Residential HVAC ductwork that is too large will result in rooms becoming uncomfortable - This duct work is TOO Big!  Duct work that is too small will increase your utility bills and perform inefficiently - This duct work is TOO Small!

Why is a Proper Residential HVAC Duct Design Important?

  1. The design of your duct work is critical for proper performance of your heating and cooling equipment
  2. A less expensive system with a proper duct design often performs better than a high SEER system with a poor duct design
  3. You have much higher heating and cooling utility bills with a poor duct design
  4. Your unit will run more often and for longer periods of time trying to condition your home if the duct layout is poorly designed
  5. Your HVAC equipment can wear out compressors if the improper duct design results in inadequate air flow
  6. Inadequate air flow can also result in your A/C coil freezing up in the summer months
  7. You will have uneven temperature distribution throughout your home resulting in a Goldilocks home - some rooms will be too hot in the summer and other rooms will be too cold in the winter
  8. Often contractors will just install an oversized unit instead of opening walls and ceilings to correct poorly designed duct work resulting in a whole new set of problems
  9. Because the unit is working harder to overcome the duct design issues, the unit may not last as long as normal
  10. If the heating and air conditioning ductwork is poorly sealed or has leaks, you can develop moisture and possibly mold issues due to condensation in the unconditioned attic or crawlspace
  11. Your HVAC equipment design, selection and installation either increases or decreases the comfort of occupants and the value of your home - Insist on an ACCA Certified Manual D duct design!

Please watch our "What is an ACCA Manual D duct design?" Video further down the page

Nationwide Manual J, S & D Services - Call 801-949-5337
Certified by ACCA in Manual J load calculations

What is Manual D?  ACCA Manual D duct design properly sizes HVAC supply and return ducts and registers to ensure heating and cooling is distributed properly to each room.  The ANSI-recognized national standard for residential HVAC duct is Manual D, from the Air Conditioning Contractors of America (ACCA), and provides a single set of duct sizing principles and calculations that apply to all duct materials.  Manual D provides system operating point (supply Cfm and external static pressure), and a method for determining the impact of duct friction and fitting pressure drop on blower performance and air delivery

ACCA Manual D® - Residential Duct Systems
Residential Manual D HVAC Duct Designs
520 N Main Street, Suite 328 Heber, UT 84032
(801) 949-5337

Nationwide Manual D Ductwork Sizing Service - Call 801-949-5337 Today!

ACCA Manual D® - Residential Duct Systems

Be sure to check out our webpages on What is Manual J? and What is Manual S? - It will help you familiarize yourself with the Manual J, S & D Process