To answer your question, no, you normally cannot supply too much return air. If installed in a certain fashion, with bedroom doors closed, it is possible to put a single room or two under negative pressure but that won’t affect the amount of heat entering the room substantially.

To calculate the filter grill size, divide the airflow, (CFM), by 2. One filter grill or the total area of all grills must equal at least 600 square inches of area to adequately supply the system with the air needed to operate.

2 CFM per square inch

Calculate the square root of the total. (Example: 4 (ton unit) x 144 square inches = 576 squared. The square root of 576 is 24. Therefore, your return air duct and grill size will be 24 by 24 inches.)

Can an air return be too big? No, an air return cannot be too big, except in extreme cases where a closed room is temporarily under negative air pressure. Return vents maintain air pressure, filter out debris, and are critical to the efficient operation of any HVAC system.

If the return duct is too small, there are an inadequate number of return grilles or they are undersized, it can’t return enough air to recirculate back into the system. This poor airflow not only makes your system run longer than necessary to provide comfort, but increases your energy bill as well.

Does Every Room Need Air Return Grilles? While it is a myth that air return grilles are required in each and every room in the house, it is definitely necessary to have more than one of these grilles installed at strategic places in the house. The most important place to have these would be the bedroom.

Your Home Might Not Have Enough Return Vents Having several return vents (ideally one in every room, but even two or three is better than just one) creates consistent air pressure. If you have one return vent, your home is fine. Keep the doors to each room open so air can properly circulate.

No, it is a code violation. No return allowed in a closet.

Cost of Return Air Plenums

“An HVAC return air duct should be in every room except a bathroom and kitchen. They should be on interior walls across the room from the supply ducts that should be washing exterior walls with conditioned air.”

In short, the answer to this question is no. Although closing off unused rooms may seem like a way to save energy on heating and cooling, it can actually force your HVAC system to work harder.

But can you really save energy by closing doors? Contrary to popular belief, closing your bedroom doors does not improve the efficiency of your HVAC system and may actually increase your utility bills.

Do you sleep with your bedroom door open or closed? You should always close your door when you go to bed. A closed bedroom door can slow the spread of flames, decrease temperatures, reduce smoke inhalation, and improve oxygen levels in the room.

In general, it’s best to keep your interior doors open as often as possible in order to allow air to flow freely from room to room. This will avoid pressure problems in your home and will make it easier for your air conditioner to cool your home evenly and with less energy.

Always keep all of the doors open when running central air conditioning. Central air runs off a blower fan and the system is balanced for whole-house cooling. Closing a door unbalances the system, causing pressure changes that suck hot air in from the outside and bleed cold air through leaky air ducts on the inside.

You should keep your bathroom door open after a shower to help prevent mold growth and keep mildew down to a minimum. Exhaust fans can pull moist air from the room, but combining it with an open door is far more effective. It will also discuss some potential situations where you may want to keep that door closed.

Closing a bedroom door reduces the air flow into the room and the air flow through the system. When the system puts air into a room and it gets trapped, it pressurizes the bedroom. This positive pressure forces the cooled, or conditioned, air out of the house through any opening in the room that the air can find.

By leaving the door open you allow the convection process to equalize the temperature in the whole space. If your room is in a shaded area with a lower heat gain then it likely will stay cooler with the door closed. But usually it is best to allow full circulation by leaving it open.

Contrary to common belief, closing off a room can actually make your heating less efficient. When interior doors are kept shut, the pressure in the room increases because the flow of air is now blocked. Any air that escapes will be replaced in an equal amount by outside air.

The less clutter you have in the room, the more available space there is for the heat to disperse and the faster it will cool down. A lot of clutter can also restrict airflow, making it feel even hotter in the room.

If there is a cold room in your house, the problem has likely been caused by dirty vents, cracked ductwork, worn insulation or faint drafts. Read on to learn how to fix a cold room in your home.

5 Ways to Improve Airflow in Your Home

1. Check Vents and Registers. One of the simplest things you can do to increase airflow in your home is to check the vents and registers in each room.
2. Turn on Ceiling Fans. Another simple solution for improving airflow is to turn on your ceiling fans.
3. Schedule HVAC Maintenance.
4. Consider Duct Cleaning.
5. Invest in a Ventilator.

To handle this problem, there are four common ways to improve cooling on your second floor.

1. Set the fan to be on all the time.
2. Make the second floor return vent & duct bigger.
3. Add a small return vent/duct to each room on the second floor.
4. Divide the house into two zones, one for each floor.

Both conditioned air and exhaust ducting suffer from a common installation problem: the airflow at the duct is being reduced at installations with flexible ducts. Two of the most common offenders are closely related: tight bends at changes in direction and crimping of the ducts at other trade components.