Furnace Air
Does Your Duct Work Leak Air and Waste Energy?
One of the easiest ways of telling whether or not your duct work has leaks is to simply open your eyes and look for the signs that professionals would initially utilize.
When I walk into a home for the purpose of giving an estimate to replace an existing furnace or air conditioner, one of the first things I do is look for signs that might approximate the age of the existing system. I walk into the home and immediately look to see if the heated or cooled air comes out of the ceiling or the floor. If the air comes out of the floor, my job is really easy. I walk to the diffuser in the floor(the air grill) and I pull the grill up and expose the sheet metal can beneath it. I am specifically looking for two things here. The type of duct work that is connected to the can and whether or not the can is just jammed into a hole in the floor with no sealing allowing air to escape around the can/floor connection or if the can is sealed with caulking or tape.
The type of duct work gives me a really good indicator as to possible leakage. If the existing duct work is metal, I look to see if there are sheet metal screws holding the duct work to the can or not. Simply look down into the duct , down to the point where the duct turns into an elbow and there you should be able to see some screw threads sticking through to the inside of the can indicating that screws are holding the duct system together. I have come across a ton of old duct systems that were merely taped together, and after years of service, the tape and its glue dry out and the tape no longer seals the duct system.
If there are screws it does not mean your system is sealed with tape or paint, it merely indicates that the ductwork is probably held together with screws through out the system. metal duct usually is put together in either 3-6 or 10 ft sections. If it is metal, the chances of the system using tape to seal it is quite high, as 30-40 years ago they did not use a painted on sealant like we use today. Your chances of having tape as a sealant and having that sealant dried out and no longer doing it’s job are quite high, but you should keep on looking for other signs of leakage.
Generally in my experience if there are no screws in a metal duct system at the boot connection, then most likely the system was taped together and if you have ever had anyone crawling around your sub floor and it’s tight, then the chances of breakage or leakage of the system are increased greatly.
If your furnace is in the garage or a closet and you can physically see it, then look to see what type of insulation was used to insulate it. If it is pink or yellow insulation, look for dark stains that would indicate air leakage. This is an indicator on yellow and pink insulation because what occurs is that air leaking out causes dust to build up around its leakage points and this dust build up leaves black lines along the entire leakage connection. I look for large and small dark stains on the insulation and if I see them, I pull the insulation back and look to see if there is a sheet metal connection behind the insulation that is not sealed. If there is a connection behind the insulation that is not sealed then I have a good idea that if the installer missed this easy to see easy to seal connection, they obviously did not take care where the connections were more difficult to get to.
I am positive at this point, there is at least a 90% chance that the system has leakage-especially since I had just found evidence. I would recommend at this point that when they have the furnace or air conditioner replaced, that they have good quality duct sealing done to the system.
If you happen to have a good digital thermometer another thing you can do if the ductwork is metal and located in the sub floor, is to make sure the system is off and then measure the temperature of the sub floor area before you turn the system on. Lets say you open the crawl space hatch and put your thermometer down there for about a minute or so.
Read and record the temperature, suppose that you measure your sub floor temperature with the system off and read it to be 50 degrees. Then go turn your system into heat and turn the temperature dial all the way up as high as it goes. Let the system run for about 15 minutes.
You will have some heat gain simply from a lack of insulation in various parts of the system and can expect a small increase in temperature, but if after 15 or 20 minutes you measure that the sub floor temperature has gone up by 5 -10 degrees or more, I would suspect that there is at least some significant leakage.
However, if you do not read any temperature rise it does not indicate no leakage. This might only indicate that leakage is not near the point where you made measurements.
The best way to identify leakage is with a duct pressure test or to crawl around and physically look at every piece of duct in your system for leakage indicators.
Good luck.
About the Author
John Grisler
Heating Air Conditioning Refrigeration
23 years Field Experience Diagnosing Troubleshooting Repairing and Installing systems
Licensed Contractor since 1991
C-20 & C-36
Field of expertise – Residential & Light Commercial Air Conditionig and Heating
Expertise: High Efficiency residential Heating and Air Conditioning equipment installations and repairs.
Our web site: greenfeetco2.com
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