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BLOWER DOORS & AIR INFILTRATION
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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
DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
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 GUIDE, AIR CONDITIONERS / HEAT PUMPS
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
Water, condensate, or ice formation in air conditioning or heating ductwork: here we explain the causes and cures for problems of condensation, water, or ice formation in heating or air conditioning system duct work. We describe and include photographs of various sources of water, leaks, or flooding in HVAC ducts and we describe the IAQ and health problems that these conditions can cause, along with recommended solutions.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Causes of Condensation, Water or Ice Formation in Duct Work, What Happens, How to Prevent Condensate, Icing, Leaks in & From Ducts
Warm Indoor Air Convection Currents Entering Cool HVAC Ducts
Our page top photo, courtesy of Indoor Air Care, shows water inside of flexible ductwork. Are these due to roof leaks, condensate leaks into the duct system from the air handler, or condensate due to convection air currents entering the HVAC duct during the heating season?
Readers should also see WET CORRODED DUCT WORK and see FROST BUILD-UP on AIR CONDITIONER COILS where we describe build-up of ice on the cooling coil in air conditioning air handler units. Also see TRANSITE PIPE AIR DUCTS (asbestos hazards) and SLAB DUCTWORK where we catalog the functional and environmental problems found when HVAC air ducts are routed in or below floor slabs
In freezing climates such as New York where some homes route their top floor HVAC ducts along the attic floor, sometimes that ductwork is not well insulated and just as it gets too hot in summer (increasing the cost of air conditioning), in winter the same ducts become too cold, increasing heating costs.
But something else funny can happen in homes with attic ducts that are used only for air conditioning.
One of our clients called us to investigate a claim that had resulted in litigation against the company who had installed a new roof on their home.
The owner claimed that the roof was leaking. The roofer claimed that the roof was perfect. What was curious was that the roof "leaked" only at the end of winter, and at times when there had been no rain and when there was no melting snow on the rooftop.
What we observed was the following causes of ice in the air ducts:
The duct ice problem was occurring because warm moist air was circulating by convection during winter, rising up into both the supply and return registers, flowing through the duct work, and leaking out of an open air handler. As the warm moist air entered the attic, the ducts were absolutely freezing cold. Moisture first condensed, then formed ice inside the duct system.
Ice accumulated in the duct system throughout the winter a little at a time, until it was several inches thick.
When the weather warmed all that ice in the ducts melted and leaked back out into the upper floor in a stunning flood. The owners, who were not thinking particularly clearly about whether or not it was raining or whether or not there was melting snow on the roof, saw that it was "raining inside" out of their air conditioning ducts and through other ceiling locations (since the ducts were not water tight there was leakage out of the ducts at other areas besides just at the supply and return air registers.
The solution to this problem had these components:
The roofing contractor was happy with this solution and the building owner was relieved as well. Perhaps because their roof had previously been leaking, before it was replaced, when they saw water coming through their top floor ceilings they thought that it was still leaking. Of course the ice in ducts problem won't occur in homes which use the same duct system for winter heating, nor will it occur in climates where freezing weather is uncommon, though we still might see some surprising in-duct condensation in some cases.
Water leaks into rooftop commercial ducts are common if the ducts were not properly installed and sealed against the weather. Especially when duct insulation is located inside of the HVAC ducts water leaking into the system invites mold and pathogenic growth in the HVAC system.
Our photos show water stains on duct interior insulation (above left) and ponding on a tar-coated rooftop commercial HVAC duct system (above right).
If you are using a central humidifier, typically turned on during dry winter months, be sure that it is not leaking onto your furnace heat exchanger - a source of costly damage and potentially a dangerous rust hole and heat exchanger leak of carbon monoxide into building air.
An improperly located or mal-adjusted central humidifier can blow excessive moisture into the HVAC duct system, a potential source of duct damage or mold growth in the air handling system.
It's common, especially in very humid areas, for condensate to blow off of the cooling coil and into the HVAC duct system. See BLOWER LEAKS, RUST & MOLD for details. As reader Joe Hartoebben pointed out, this problem may be more serious if the air handler's condensate drain pan and drain piping are not working properly as the combination of high humidity (typical for example in Florida) and inadequate condensate handling will invite the blower to send condensate water droplets blowing down the duct system.
Frequently Asked Questions (FAQs) About Cleaning, Salvaging, or Replacing Flooded Air Ducts in Air Conditioning or Heating Systems after a Fire, Flood, Hurricane, or other Disaster
Question: I Fixed Condensation Problems in my HVAC Ducts, but Now I Have Metal Chimney Condensation To Cure
First I must thank you for your article on condensation in conditioner ducts that are in the attic and not used for heating (WATER & ICE IN DUCT WORK). I had the same problem as in your article and had several AC techs and a P.E. look at the problem and not one of them could come up with answer.
Since I blocked the return and register grills the problem disappeared. Perhaps you could suggest an answer to another problem.
I have a gas boiler and a separate gas hot water heater in the basement. I have a metal chimney into which they are connected. The chimney goes up through the roof. The chimney extends about three feet below where the boiler flue and gas flue are connected. I am getting condensation dripping out of the bottom of the chimney pipe - there is not a large amount and it appears to be coming down the inside of the chimney and then leaking out. Any suggestions? Thank you for your help. F. D. - Mattituck NY
Check These Chimney Safety Worries First
A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem. That said, here are some things to consider:
Watch Out: I'm afraid that those conditions are likely to be unsafe and could include a carbon monoxide hazard - so be sure you've got working CO detectors.
Question: Hurricane Sandy flooded fiberglass heating ducts in our crawl space - can't we just run the heat to dry them out?
During hurricane Sandy the sump pump in my crawl space failed and my fiberglass heating ducts were partially submerged for two days before the water was pumped out. I replaced the sump pump and got an estimate of $7600 to replace the ducts. This may not be covered by insurance. Is it essential to replace the ducts or will the heating air dry them out sufficiently to avoid mold? - I.E.
Reply: Running heat to dry out flooded ductwork is a risky proposition and may be unsafe, as we explain here
A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with water entry, ductwork or an HVAC system. That said, here are some things to consider in deciding how to handle flooded ducts after Hurricane Sandy or similar events:
What are the Risks when Duct Systems are Flooded?
The risk of flooded ductwork, assuming that the air handler, furnace, and controls were not themselves flood-damaged as well, includes more than potential mold growth inside the HVAC system. Floodwaters usually contain sewage and sewage pathogens that can also be a source of serious infections or illnesses.
Even when materials wet by sewage-contaminated waters have dried, dust from the dried materials is likely to be unsanitary and to contain pathogens that can in turn cause illness.
When contaminated dust blows through the duct system it first contaminates the rest of the HVAC system - blower fans, air handler, plenum chambers, heat exchanger, filter systems, other ductwork, supply and return registers. And when such duct reaches room air and can be breathed by occupants it presents a health hazard.
Those same health and HVAC contamination hazards are repeated as a mold risk. Duct insulation that is actually mold contaminated may or may not be *visibly*contaminated, as you can read in our article about fiberglass insulation mold at FIBERGLASS INSULATION MOLD
Metal ductwork that is accessible can often be cleaned (photo above left) but any external duct insulation that was wet or contaminated will need to be replaced. Other types of ductwork that cannot be reliably or safely cleaned after flooding are described below.
Other Problems Occur due to Ductwork Flooding, including
Incomplete duct cleaning and replacement: we saw this water-soaked fiberglass-lined HVAC duct at an office building where the owners had been assured that all previously wet ductwork had been replaced and that there were no leaks into the duct system.
Insulation that has become wet and soggy can sag, collapse, block the ductwork completely, or partially block ductwork increasing air conditioning or heating costs and reducing system effectiveness.
Loose fragments of duct insulation, if drawn into the blower assembly, can jam the blower fan, leading to a fire.
The problems with wet HVAC ducts due to flooding include more than water, sewage pathogens, and mold contamination risk. There is also the problem of mud and silt that enter flooded duct systems. I've found inches of fine muddy silt on the bottom of ductwork in flooded buildings I've inspected.
Dirt and debris blowing through the duct system clogs the blades of the squirrel cage fan type blower fan in the air handler, reducing air flow, causing air conditioning or heating system malfunctions as a result, and of course also reducing system effectiveness and increasing system operating cost. Details are at DIRTY A/C BLOWERS
That same dirt and debris in the duct system is likely to block the cooling coil if the system includes air conditioning, causing icing and malfunction described at DIRTY COOLING COIL
Advice for Salvaging Flooded Ductwork - Avoid Running the HVAC System
Did anyone run the heating or air conditioning system after it was flooded and before it was inspected and cleaned?
If so the entire system is a candidate for professional cleaning and sanitizing for the reasons we explained above. It's best not to run heating or air conditioning, even if it's operational, if that system has been flooded, or if the building has known mold contamination, until those problems have been addressed, as doing so contaminates the system and spreads airborne pathogens increasing the risk to building occupants.
As you can see in our photo (left) fiberglass insulation in this air handler is quite vulnerable to wetting and contamination by floodwaters.
We might make an exception to that advice if experts on site determine that the benefit from running the heating or air conditioning system to speed building dryout are worth the costs in damage to the system itself, and of course provided that appropriate cleaning or replacement steps are going to follow. This situation might arise following widespread flooding or disaster when there are simply not enough free-standing air movement, fans, dehumidifiers and building dryout equipment to service all of the buildings in need.
What sections of ductwork were actually flooded - certainly all sections that were wet by floodwaters need to be addressed?
Important in Deciding how to Treat Flooded Ductwork is the Question: of what are the HVAC ducts constructed and where are they located?
Impact of HVAC Duct Routing & Location on Cleaning & Restoration Costs
What about Just Spraying a Sanitizer or a Coating Inside the Flooded Ductwork?
What about just spraying a sanitizer or a coating that seals the internal surfaces of fiberglass ductwork? This approach is worth considering for ducts that were not actually flooded but are suspect of contamination and not easily cleaned or replaced.
However there are some warnings to keep in mind, including the difficulty of assuring that absolutely all surfaces are coated and sealed and difficulty of assuring that the sealed surfaces remain intact throughout the remaining life of the building.
We have inspected sealed ductwork in which it was quite obvious that the spray procedure did not find and cover all of the contaminated surfaces and we have found other sealed ductwork in which later "sealed" sections fell away. Both of these defects exposed building occupants to air contaminated by mold or sewage pathogens or other pathogens that can occur in some duct systems (such as due to bird or rodent invasions).
More examples of damage caused by water and flooding to HVAC ducts are at WET CORRODED DUCT WORK where you will see photos of more rusted or deteriorated ducts.
Questions & answers or comments about the detection, cause, effects, and cure of water or ice formation or flooding in HVAC ducts.
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