Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE EFFICIENCY RATINGS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of Heating & Cooling Terms
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
Heating & air conditioning HVAC ductwork air flow balancing: this building air supply ductwork diagnosis and repair article describes proper (and improper) balancing of heating & air Conditioning duct air flow in residential buildings and in commercial office space including high-rise buildings. Our page top photo shows how individual office occupants who are too hot or too cold can foul up carefully balanced air distribution in a building. Just push over a section of suspended ceiling.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved.
Look for indications that the system has not been balanced for optimum air flow:
You may want your service person to review air flow in different rooms, to add manual balancing dampers in the duct system (and show you where they are located and mark on the duct just where the balancing damper levers are normally set.
Air conditioning cool air balancing in offices & commercial spaces or in homes with long HVAC duct runs
The photographs above show both supply and return ceiling registers in a commercial office space. In this case they are located too close together. The second photograph (above right) shows that a ceiling tile has been removed from a suspended ceiling over an office which uses the ceiling cavity as a common return air plenum. While this may produce more airflow in the office where this suspended ceiling tile was removed, it has unbalanced the entire air conditioning system for the rest of the offices in the building.
Many commercial spaces and offices are cooled (and sometimes heated as well) by an air handler which delivers supply air to each office area by flex duct connected to ceiling registers.
Return air is passed back to the air handler through the large common space above a suspended ceiling over the occupied space.
Special vents either around the supply registers or placed separately are intended to pass return air to the common ceiling space, and their location and adjustment are important to provide balanced airflow in the work space.
Single Return Air Inlet & Un-Balanced Cooling or Heating Airflow
Use of a single return air location invites un-balanced air flow delivery into various rooms in a building, especially if room doors are left shut and there is no provision for air movement out of closed rooms to the central return register.
In addition, distance to the central return air register, obstructions, or circuitous routing through hallways or even among different floors in a building all argue that a single central return air register can contribute to an air-starved air handler or uneven air delivery to the conditioned spaces.
Poor Heating or Cooling Air Flow & Debris & Contaminants in Ceilings Used as Return Plenums Risk Entrainment in Building HVAC Airflow
This photograph shows a common ceiling plenum over a commercial office space in a Manhattan high rise building. Notice the considerable amount of debris atop the ceiling tiles?
All of the office conditioned air moves through this area, risking additional levels of irritating or harmful particles, particularly if the debris contains asbestos fragments or lead paint chips. (In this particular case tests showed that this was not the case.)
Here are some common concerns or defects in commercial installations that use this design:
These photos show a common ceiling return air plenum over commercial offices. In the first or left hand photo, notice that rectangular opening in the distance? The second photo is a close-up showing a big surprise: the ceiling area used as return air plenum for an office suite is wide open to the rest of the building ceilings on the same floor.
Openings had been left open between the office space and the top floor hallway and also between the hallway and other office spaces in the building, so that particles, leak-related mold, or other irritating particles developing over any office will be shared among all of the tenants on this building floor.
Watch out: unanticipated or improper openings between building areas may also be a fire hazard, contributing to the rapid spread of fire from one building area to another. See FIRE DAMPERS in DUCTWORK. Also see UNSAFE DUCT OPENINGS.
Missing or incomplete ceiling partitioning in large commercial buildings may mix air (and odors or contaminants) from multiple offices or building use areas, redistributing these un-wanted odors or particles to other building areas. One of our clients who maintained a law office in a strip mall complained of chemical odors which were traced to a beauty parlor located at the extreme other end of the building.
Open windows, especially in a tall office building such as shown by this photograph, cause a tremendous up-draft through the building, moving particles, gases, or other potential IAQ concerns up through the building.
In this instance the office occupants on the 18th floor of this Manhattan office opened their windows and also their office entry door to try to cool off their offices because they were unable to turn off the building heating radiators.
Other Causes of & Cures for Un-Balanced or Poor Air Flow Through Commecial or Long Residential HVAC Duct Runs
In addition to the HVAC air duct flow balancing problems & recommendations discussed above, consider these possible causes of inadequate cool air or warm air deliver to some building areas:
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Question: forms for commercial air duct flow balancing for a retail building?
I need forms for commercial air balancing for a retail building. - Kevin Ryan, Oct 2012
Kevin I am doubtful that "forms" will be enough to balance air flow in a retail building; the HVAC duct design has to consider quite a bit of information beyond what's in a duct layout sketch form. I'd start by making a drawing of the existing system, including duct diameters, lengths, bends, and location of supply and return registers; You may need to consult an HVAC design engineer, but some defects will become obvious simply by examining the duct layout.
Doing so, we found that a duct section had fallen off; thet sensor that told the site engineer what was going on was still happily reporting that air was blowing into an office space when in fact all of the cool air was blowing into the building's attic.
Question: How do we get cool air to the more-distant, hotter end of our house?
Your site is fantastic. I am a home owner that needs a cheap but through education because of a bad remodel. My question is: my home is a one story shaped like a rectangle. We have a brand new AC unit. One end of the house is cool and very comfortable. The very end of the house is always much hotter. If we cool the entire house we have to set the thermostat at 65 degrees. So the really cool end of the house is like a meat locker and the other end is just comfortable.
I know this could be a duct problem or it could be the wrong size unit was purchased to begin with. We have a 5 ton - maybe we needed two smaller units? Did I mention I live in Phoenix AZ? What is the logical way to start? If I missed this issue on your site you could tell me where it is. thanks. - G.B. - Phoenix, AZ /p>
Reply: priority of things to try to improve cool air (or warm air flow) across a building with long HVAC duct runs
Before doing something expensive like installing a pair of new A/C units and separate HVAC cooling duct systems to make cooling distribution more effecive across yoru home, and presuming there is a complete house HVAC duct system already installed, I'd have considered these steps:
Those components should be much less costly than system replacement and redesign.
Question: shared return air opening among 3 air handlers, only one condensate pump operates - why?
I have 2 furnaces and 1 down flow furnace, sharing 1 common return.I am wondering if given the set up why would only 1 condensate pump turn on when called . It is always the same one. The down flow does not have a pump.My thinking is that the air flow favors the one pump. - R.K. 10/1/2013
Reply: unbalanced air flow is likely in the system you describe; here are various reasons why just one of three condensate pumps seems to be running
A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. For example onsite one might find details about how air actually flows through your system. You will find additional depth and detail in articles at our website. That said I offer these comments:
I infer from your question that the root concern with your HVAC system is one of improper air flow or flow balancing among three air handlers sharing common return ducting.
A single air return feeding three air handlers could face at least these technical hurdles:
1. inadequate total air return to all 3 air handlers, resulting in an air-starved system at one or more units and un-balanced air flow through the total duct system
2. Poor location of return air for one, two, or even all three systems. With a single air return, for example, if the door to a room is shut there may be poor delivery of conditioned air into that room.
You are asking about condensate handling which in turn leads one to assume we're talking only about cooling or air conditioning conditions. It would be no surprise for the cooling load to be very different in various building areas; for example upper floors or floors with lots of glass and thus solar gain have a higher cooling load (in general) than other areas.
Unevenness in cooling load, OR, as you speculate, unbalanced airflow through the system could cause just one condensate pump (presuming one pump per air handler) to operate more often than the others.
Watch out: check that all three condensate pumps are actually operating, and that each properly drains to a suitable location. We don't want condensate leaks into the building.
Summarizing: in concept one would be looking at your HVAC system for duct design and air flow balancing problems and once understood, one would choose a method (duct dampers, more air returns, fan speed adjustments, supply register adjustments, more return air flow openings between rooms, etc) to improve system performance.
Questions & answers or comments about how to balance air delivery or air supply in duct systems for building heating and air conditioning.
Ask a Question or Enter Search Terms in the InspectApedia search box just below.
Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.