Extra AC return vent

[William Merritt]

Five yearsago I retired from home inspecting because of my age. I miss it. However, neighbors use me a sourcesif they need advice concerning their house (naturally free of charge) whenthings go wrong. Yesterday I was askedif I could determine why the AC was not cooling correctly at the rear of myneighbor’s house. The occupant wassleeping in the front bedroom because the rear master bedroom was hot. The house is 10 years old. The front bedroom outlet air temperature,adjacent to the AH which is in a laundry room closet, was 69-degrees while themaster bedroom at the rear of the house (60 feet away) was 86-degrees. The return air register is adjacent to thefront BR wall and about 15 feet from the air handler. I pulled the filter from beneath the AH coils. Ice cold water poured out along with aplastic Target bag that was stuck to the filter! The filter looked like it had been sprayedwith black paint. AH coils wereextremely dirty also. I looked under theAH and found that an 8” x 10” hole had been cut in bottom of the returnduct. This answered the question ofwhere the plastic bag came from. The baghad been sucked into the system. I did atemporary patch over the hole using cardboard and put in a new filter. The air temperatures immediately balanced outthroughout the house. The rear bedroomvent air dropped from 86 to 72-degrees. I suggested that my neighbor call her landlord, tell him what I hadfound and done, and recommended that the duct be repaired “professionally”, andto request that the AC system be cleaned. The landlord said he knew about the hole. He said that the AC service guy had cut thehole to “improve air flow”. What would the logic be?

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[Bob Harper]

If the ducts were not designed, sized, and installed properly, you can get bad airflow problems. One way to cheat around this is to hack a hole in the return. It causes more problems, not the least of which is depressurization of the Combustion Appliance Zone which can lead to backdrafting of atmospherically vented appliances and CO poisoning. If total electric home, it still ruins the ventilation and air quality due to air stagnation in the rooms while inhaling the CAZ air along with whatever else is in that air.

If there has been blow-by of the filter the A-coil is most likely clogged and grossly inefficient. Press to have professional HVAC service including measuring duct pressures once the ducts are properly sealed. The codes now require the returns be sealed for the first 10 feet back from the AHU.

[Dom D'Agostino]

There's an extremely large quantity of poorly ducted homes here in Florida. Insufficient return air is all too common.

I bet the landlord told a tech to cut the hole as a cheaper way of "fixing" a previously reported problem.

A ten year old HVAC is that poor condition should be replaced. A full coil cleaning (removing the coil from the AHU) will cost $400, not including the duct repairs and whatever else is wrong, so I doubt the landlord will repair or replace it unless it explodes.

[William Merritt]

The AC service person came out this morning, along with the landlord. He said the problem was the filter and removed my patch over the hole. I'm not the smartest AC person around but I do have something the this service person apparently doesn't have .... common sense! Thanks for your input. I really appreciate the code reference.