Monday, May 27, 2019

Moisture Stains on My Ceiling or Dark Stains around the HVAC Vents Covers



Moisture stains around vent cover on ceiling 1homeinspector.com
A lot of homes we inspect in Florida have condensation on the HVAC duct vent covers and moisture stains or mold on the ceiling around the vent.  The cold air from the vent coming in contact with warm air at the ceiling or uninsulated duct boots in the attic causes condensation to form on the vent covers.  Frequently, this condensation causes moisture stains on the ceiling.  The moisture stains can be an ongoing challenge if the cause of the condensation is not addressed. 

The water marks on the ceiling and the droplets of moisture on the vent cover are likely caused by insufficient insulation on the ducts in the attic, inadequate insulation or uninsulated vent boots, or leaking of hot / warm attic air around the vent boots. 

What is a vent boot?   

The vent boot is the box in the attic that the air conditioning duct connects to on one side and the vent cover on the ceiling is screwed into.  Newer boots are often constructed out of insulation board or duct board.  The older types of boots were constructed out of metal.

uninsulated duct boot in attic 1homeinspector.com The above picture shows an uninsulated vent boot attached to the HVAC duct.  The vent cover connects to the vent boot on the inside of the ceiling.  This boot has no insulation and the joints are not sealed well.  The sealant between the boot and the ductwork is leaking and there is no sealant between the duct and the ceiling.  Moisture accumulating on the vent boot drips down until it is absorbed by the drywall ceiling board causing moisture stains around the vent cover.

People often mistake the dark stains that sometime form around the vent for mold.  The plausible cause of the dark stains is the vent boot was not sealed to the ceiling board.  The dust from the attic, then sticks to and stains the moist drywall board around the vent cover.

When you see the stains around your ceiling vent covers don’t ignore them.  Water damage is costly to repair and moist conditions may encourage mold growth.


Random Moisture Stains on your Ceiling


HVAC duct joints leaking in the attic - 1homeinspector.com

If you have random stains on the ceiling; it may be the joints are not sufficiently insulated or sealed.  Moisture stains are visible at the joints of the ductwork in the attic in the picture above.  Condensation forms on the joint and may not evaporate in the attic.  If the condensation continues to drip, it may saturate the insulation and cause moisture stains on your ceiling.
Recommendation:   We recommend sealing the joints to prevent cooling loss in the attic and random stains on the ceiling.  Sealing the joints will also improve the efficiency of your HVAC system and help reduce your cooling costs.

 

Main Causes of Condensation at AC Vents

Not enough insulation on the ducts themselves

Cold air traveling through your ductwork in a warm or hot attic forms condensation if the duct is uninsulated or under insulated. The air ducts in the attic should be well insulated.  You should have your air conditioning system and ducts inspected if it struggles to maintain a comfortable inside temperature on hot days or you notice condensation on the ceiling or vent cover.
Insulation damaged on HVAC ductwork - 1homeinspector.com

The insulation on the duct above was separated from the duct.  Condensation had formed in the duct vapor barrier and over time had stained the middle of the ceiling.
Recommendation: Ducts in the attic should be well insulated and in good repair.  Damaged or old under insulated ducts should be replaced.  Consider replacing the ductwork in the attic if it is 20yrs or older.  It will be a good investment that will be easily recouped and will save you money on your future electric bills.

Uninsulated vent ‘boot’

The metal box in your attic that attaches to the duct and the vent cover screws to is the boot.  In an attic in Florida, the uninsulated boot will generate large amounts of condensation due to the cold air in the boot and the hot air in the attic.
Above is an uninsulated galvanized duct boot. This boot was cold in the hot attic and caused water to condense on it and drip onto the ceiling.
Recommendation:  We recommend having an HVAC contractor evaluate the condition of the ductwork.  Sealing the duct to vent boot joint and insulating old metal ducts will help reduce condensation around the vents.  Older deteriorated ductwork should be replaced.

Dark Stains around your vent Cover

Dark stains around your vent covers may be mold, but more likely it is dust collecting on the damp ceiling.  If the boot is not properly sealed to the ceiling, it will allow attic dust or dirt to seep out of the crack between the ceiling and the vent cover.  Also you may discover a leak where the vent boot attaches to the duct. If not properly sealed, the cold air leaks out, meets up with the warm attic air and creates condensation.

Recommendation:  Find and seal the leak. If the problem vent is easy to access from your attic, you may be able to check for and fix the problem yourself. We recommend consulting with a local HVAC contractor to evaluate and repair the HVAC ducts. 

Covering Stains around the Vent Cover

The dark or water stains around your vent cover are difficult to cover.  When the repairs have been made, the ducts have been caulked and no more condensation is present on the covers it will be time to cover the stains. 

Normal ceiling paint will not cover up these stains.  Moisture and dirt stains around the vent cover are stubborn stains.   Even with multiple coats of ceiling paint, the stains continue to bleed through the ceiling paint.
Recommendations:  We recommend you first cover the stains with two coats of KILZ 2 Multi Surface Primer & Stainblocker then paint with your choice of ceiling paint.




Frank Carr is the Owner / Inspector at First Choice Home Inspections in Deltona, FL serving Volusia, Seminole, Orange and Lake Counties. Formerly in the building trades, Frank’s focus is a safe home in the Orlando Metro and Daytona Beach areas of Central Florida and building FCHI. We believe that consumers have the right to expect the highest standards of thoroughness, fairness and effectiveness from their home inspector and that is exactly what we provide.
 
First Choice Home Inspections
Residential Home Inspections in Central Florida
(386) 624-3893 


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