Gazette Articles

July 2004
GAZETTE Newspapers
By: Arthur S. Lazerow

Ask Mr. Home Inspector

Air Conditioning and the Importance of Return Air

Question: Francis from Catonsville, Maryland emailed the following question last week:  We are living in a home built by (a national homebuilder) that is about 12 years old.  My problem is that they installed a central return stack.  Thus the only return vents are in the first and second floor halls.  The first floor cools fine, but the only way the bedrooms can be comfortable is to keep the doors open and run fans to get the heat out of the hallÉ. Can the house be retrofitted with returns in each bedroom?

Answer: The problem of an imbalance in the air return system is extremely common.  In reality, the air handler fan pulls the return air back to the furnace, which depressurizes the living spaces and gives permission for the supply air to exit the registers and condition the rooms.  Enough theory!  I discussed FrancisÕ question with my heating/air conditioning contractor who I know to be both knowledgeable and honest.  Here are some thoughts and suggestions:

Does the home have an attic fan through the roof?  Reducing the air temperature in the attic through improved attic ventilation can have a significant impact on the temperatures of the second floor rooms.  It will be easier to cool the second floor and you will save money.

With respect to the air conditioning equipment, my first thought is to determine that the system is cooling properly.  Take the temperature with a long-necked meat thermometer at the first floor return grille and also at a nearby floor register, with the system operating in air conditioning and the fan in the ÒonÓ position, not ÒautoÓ.  The difference between the two temperatures should be between 14 - 20 degrees.  This number is called "Delta T" and is significant to HVAC contractors.  Too low a ÒDelta TÓ indicates in most cases a refrigerant gas problem.  Too high a ÒDelta TÓ indicates lack of airflow across the coil, due perhaps to a clogged air filter or a blockage in the ductwork.  Satisfy yourself that the system is cooling properly.

The CFM at your returns should total about 400 CFM per ton of air conditioning.  The typical homeowner has no way to measure CFM.  Try this simple test: take a piece of 8 1/2 x 11 inch stationery and hold it up to each return.  The paper should be pulled flat and held on the face of the return.  Try to determine if there is an apparent difference in suction between the first and second floor return grills.

Then try this experiment.  Completely block off the first floor return and close down as many first floor registers as possible.  Live with that for a day or two.  You should not do this experiment for any length of time because it strains the equipment, but this will show that it is possible to cool the second floor.

Finally, many main airflow duct systems have built-in dampers.  To balance airflow, adjust these.  In the summer, fully open the damper in the main duct serving the second floor and turn the handle of the damper in the first floor main supply trunk 45 degrees to restrict the air flow to the first floor.

Once all these tests have been performed and the system simply does not cool the second floor, you have two alternatives, besides the attic fan idea mentioned above.  Since FrancisÕ home is 12 years old, the outside condensing unit is nearing the end of its useful life and he is facing the normal replacement cycle.

Alternative One:  When the current outside condensing unit is replaced, have the HVAC contractor install a second system with the air handler in the attic, with ductwork and diffusers in the ceiling of each room to serve just the second floor.  Abandon the basement ducts that service your second floor and use the current system with the new condensing unit to cool the basement and first floor only.  This absolutely solves the problem, period, and end of conversation.  Unfortunately, this alternative is somewhat expensive, but it is not uncommon to have two systems, a gas fired furnace in the basement, and a heat pump for air conditioning and heating on the second floor located in the attic.

Alternative Two: Carrier and probably other manufacturers make systems that are highly effective removing humidity from the house.  A dryer environment on the second floor, in conjunction with an attic fan, will make the house feel much more comfortable.  One client of my HVAC consultant had to raise the second floor temperature to 76 degrees to keep is family from complaining about the chill since the house was so dry, even though the actual temperature was on the warm side.

My original thought of an in-duct booster fan in the second floor return air duct was totally frowned upon by my consultant.  Also, the cost of installing return ducts in each bedroom as a retrofit would be excessive.  The second system is cheaper.  I hope this information helps and you obtain relief from your overheated second floor.

Tip of the Month:  Has your home been tested for radon gas?  The home test kits at Home Depot or Lowes are about $35.00.  No one should live in a home that has high radon concentrations, since radon causes lung cancer.  Remediation, if needed, costs only in the $800-$1,000 range.   If your dwelling is a townhouse or single family, or a one level home below the third floor, EPA recommends testing.  Be safe, know the quality of air you breath.

Have a question relating to a housing problem? Email it to aslaz@erols.com. Each question will be answered and some will be included in this column.

Arthur Lazerow, president of Alban Home Inspection Service, Inc., was a homebuilder for 25 years and is now a nationally certified ASHI home inspector, having performed more than 5,000 inspections during the past 10 years. He can be heard every Saturday from 10 to 11 a.m. as co-host of Real Estate Today on WMET 1160 AM.

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