Attic Air Leaking into Air Handler

[pcarpe01]

We have a Bryant system for central AC. The air handler is installed in the attic. We recently got a new roof installed - all new plywood, shingles, etc. On hot days we can smell the roof within the house. I went to the attic and noticed that air leaks where the refrigeration lines enter the cabinet. I also noticed the secondary condensate drain was not connected - which was sucking air and the air purifier cover was also leaking. When I say leaking I am referring to air being pulled into the cabinet from the surrounding area, the attic. My question is that is it common to have air leaks in the air handler and how are they typically sealed? I also need to better check the return ducting for any sign of leaks. It looks like there should be some kind of grommet over the refrigerate lines to seal the cabinet. I called the so-called experts and they look at me clueless. In any event, I sealed the above leaks using 1409 tape, at least for now, until a permanent fix is put in.

 

[Dana]

Tape all the seams of the air handler cabinet with temperature rated aluminum duct tape (eg Nashua 324A, sold in most box stores.) I have no idea what "1409 tape" is.

Electrical penetrations of the cabinet can be sealed with polyurethane caulk (not the cheap stuff), refrigerant lines too, if the gaps are reasonably small.

Duct seams and joints are best sealed with duct mastic, not tape, unless it's hard-pipe duct and very clean. The seams of duct boots can also be sealed with duct mastic far better than with tape.

Where duct boots or ducts penetrate the ceiling it needs to be sealed too, otherwise air-handler generated pressure differences can drive large amounts of air infiltration whenever the air handler is running. For large gaps a "windows & doors" type can-foam may be needed. For smaller gaps polyurethane caulk works, but pull the registers and tape over the boot to the ceiling gypsum with foil tape or housewrap tape, since the seal to the raw exposed gypsum at the hole cut is guaranteed to eventually fail.

 

[Sponsor]

 

[pcarpe01]

Thank you for the reply, but is this a common problem? Meaning air leak issues with air handlers? My parents have a Trane unit and do not have these issues. Is it brand specific?

 

[Dana]

Yes, leaks in air handlers and ducts in attics are common, and will often add a significant parasitic cooling & heating load. Most states don' t require commissioning of ducted systems with "not to exceed" leakage numbers at 25 Pascals pressure, but some do. Most don't require room to room pressure difference measurements either.

Energy Star has specs for ducted systems:

-----Duct leakage to outdoors modeled at the greater of ≤ 4 CFM25 per 100 sq. ft. of conditioned floor area or ≤ 40 CFM25.

-----Room to room pressure differences ≤ 3 Pascals under all operating conditions.

Typical non-commissioned systems are poorly designed and have several times the Energy Star max leakage. Even an order of magnitude more air-handler driven infiltration than would occur in Energy Star ducted system is pretty common.

 

[WorthFlorida]

My father once said that a home is built as good as the man driving the nail. The same with AC installations. In part your problem was the tech who installed the air handler or a service tech that came afterwards. Air handler cabinets for residential use are never 100% airtight but should be pretty close and no obvious signs of leakage. The copper lines through the cabinet should have been sealed with a sticky foam tape that installers use to seal it up. New air handlers may have a piece or two in the box since these entrance holes are where the line are brazed to the coil, then sealed after the it cools down. Others will have grommets.

Any air handler in the attic should be installed over a large drip/drain pan with a pipe leading to the outdoors. Should the main drain line plug up the condensation will not drain on the ceiling below. You may find that the overflow from the coil may only go to this pan or not at all. The main condensation line must directly be piped to the outside. At the overflow drain connection, from the factory they do have a threaded plug installed. If it was missing then someone removed it. This overflow connection is sometimes used to install a Safe T switch. You should have one somewhere.

As far as the the air handler cabinet, some are made real good, others not so good. Sometimes the cabinet is slightly twisted or not level and the frame gets a little out of square. On my own AC I once added black electrical tape to create a gasket. It actually worked. When it is real bad I've seen foil tape placed around the entire coil access panel. Then it needs to be cut to get access and it becomes a mess.

https://www.grainger.com/product/49..._on_Your_Search-_-IDPPLARECS&cm_vc=IDPPLARECS

 

[LLigetfa]

The seams of duct boots can also be sealed with duct mastic far better than with tape.

My air handler is in my crawlspace which is conditioned space so sealing all the joints was not a priority when it was installed as I needed to heat the crawlspace anyway. Later, when I added A/C to the system, I went around and sealed all the joints with mastic as it was much easier than foil tape.

I'm sure an attic installation would be insulated and so difficult to seal afterwards. Does mastic remain pliable or would it crack and fall off?

 

[WorthFlorida]

We have a Bryant system for central AC..... It looks like there should be some kind of grommet over the refrigerate lines to seal the cabinet......

Here are pictures from my own home but the air handler is in a closet on the second floor. It is a Carrier unit and would be nearly identical if it were a Bryant. This unit is three years old and in Florida, permits must be pulled by AC contractors when installing a replacement AC and must be inspected.

At the base of the cabinet where it meets the wood base it must be sealed with duct sealant and all corners and seams of the entire base. The biggest air leak area is the filter access panel. It's at the base and a real PITA to remove it to get access to the filter. Most air handlers have this same design and it stinks and a big area for air leaks. I added a filter return grill to not have to use this. Also notice that the low pressure return line is insulated right up to the cabinet. Over time the foam may degrade or the glue holding it starts to fail.

To check for leaks get some fragrant scent sticks. They make a little smoke and can be used to looks for air leaks.

 

[Dana]

My air handler is in my crawlspace which is conditioned space so sealing all the joints was not a priority when it was installed as I needed to heat the crawlspace anyway. Later, when I added A/C to the system, I went around and sealed all the joints with mastic as it was much easier than foil tape.

I'm sure an attic installation would be insulated and so difficult to seal afterwards. Does mastic remain pliable or would it crack and fall off?

Duct mastic lasts for decades. It will NEVER fall off, but in some higher-vibration environments by the time it's been flexed 10 billion times it can fail. With fiber-reinforced duct mastic even high-vibe situations (= really loud air handler) aren't a problem. (I've personally seen ~60 year old mastic on commercial ducts that still sealed perfectly, where the whistle & noise we were chasing proved to be leaks at the joints at the newly replaced hot air furnace plenum that had been poorly taped. The old hard piped ducts sealed with mastic were fine!)

Though not nearly as big a problem as when it's outside of conditioned space, duct & air handler leakage is still an issue in the crawlspace, since it randomly changes the overall duct balance, pressurizing some rooms (or the crawlspace) depressurizing others, using "the great outdoors" as part of the return path via any leaks in the building envelope. With very generous return paths designed-in the amount of pressure difference generated will be small, but doing a room to room pressure difference audit with a sufficiently sensitive dual-port manometer can tell you when it's getting way out of hand.

( WorthFlorida- thanks for pointing out the purpose-made tape!)

 

[WorthFlorida]

As far as safety is concerned, sealing returns, especially in crawl spaces, is very import for not wanting to pull in gases or fumes from other sources.
Unfortunately, there have been many carbon monoxide poisonings and deaths in Florida and I'm sure many of the sun belt states. Many air handlers are installed in garages and with the extremely quite engines and aging population, many vehicles are left running. CO will creep into any crevice and an air handler will certainly pull it into the home.

 

[LLigetfa]

The old hard piped ducts sealed with mastic were fine!

I was more concerned with applying mastic to the insulation jacket, not the metal duct. My ducts are not insulated so the mastic is applied to metal where there is no flex.

I used foil tape where the refrigerant lines penetrate the duct.

As for safety concerns pulling in crawlspace air, as I said, it is conditioned space so not any worse than a finished basement. There are no gasses down there that are not also in the living space. My concern was for the number of air exchanges WRT humidity levels. Air down there is dryer than the air in the living space and I wanted to keep it that way so that ducts don't sweat when the A/C is used.

 

[WorthFlorida]

I was going through my old laptop looking for pictures and I came across pictures of a home I worked on in 2009. It was a rental with the owner living in Delaware. I took pictures to relay to them on work that needed to be done. This air handler was in the garage probably installed 20 years earlier but the compressor was newer. It shows how nasty they can get with too many service calls and what happens when foil tape is overly used. All of the mold is from condensation. In the humid south, no matter how hard you try, condensation can almost never be eliminated with a garage installation. My A/C tech friend Paul did work on it a few months later to keep it working. I did notice a few years later the entire system was replaced.