Hot and Cold Spots

Posted in Indoor Air Quality Dec, 02, 2012

There are many things that can make a home feel uncomfortable; hot and cold spots are the most common. Answer these few questions; if the answer is “yes” then you have a problem!

  1. Is there a room that you need to adjust the thermostat for (lower or higher) for the room to be comfortable?
  2. Is there a room where, when you close the door at night, you feel uncomfortable even though the thermostat is at the temperature you want?
  3. Do you need to have an additional fan in the room to make it comfortable?
  4. Do you avoid cooking in the summer because it gets too warm in the kitchen?

What Causes Hot and Cold Spots?

There are many things that cause hot and cold spots in a home. The two most frequent in my experience are:

  • Incorrectly sized ducts
  • Lack of proper return air grilles

Incorrectly Sized Ducts:

Many times the hot or cold room is the farthest from the indoor unit. In Texas, where flex duct is king, this often results in poor airflow to this area. Why? Well, flex duct is a highly restrictive duct design; all ducting has some amount of restriction.

Flex ducts, with its highly restrictive design, that are very long do not allow the proper amount of airflow. This is due to several things, but in reality it is usually because the wrong size has been used and the flex duct is not installed correctly.

Sizing a flex duct branch is an easy thing to do correctly; yet again and again I see flex duct branches that are too small, too long or have too many changes of direction. There is a right and a wrong way and, lucky for you, we know how to do it right!

Correcting this may be either a simple matter or a complicated matter. If all of the duct is accessible than correcting is easy. Either up-sizing the flex duct branch, adding a highly efficient fitting or a combination of both will greatly improve airflow and comfort!

Along with incorrect size is, often times, incorrect installation. Flex is easy to bend around obstructions; but it is designed to be in a straight run! These images below show some flex that is severely restricted due to kinks.

Lack of Proper Return Air Grilles

Air must move, like a fluid, to keep the home comfortable. If you close a door to a room, like a master bedroom, then that room becomes uncomfortable the likely culprit is too little return air.

Once the door is closed the supply air will pressurize the room; as the room pressure increases less and less supply air can enter.

Think of a bucket that you can fill with water. If you have a valve close to the bottom of the bucket you can open that valve and start filling; if everything is balanced the same amount of water will leak out of the valve as you are adding and the bucket never gets full. Now close the valve and start filling; pretty soon the bucket is full and no more water can be added.

You room is the bucket and the water is airflow; by installing a ‘valve’, or return air grille, in the room we can keep adding new, fresh, cold air because we are removing the same amount of old, stale, warm air via the return grille.

What to do?

As you can see above, I have no shortage of images of improperly installed flex ducts!

The easiest option for the homeowner, or building owner for that matter, is to call us for a home system performance evaluation. This evaluation will determine the extent of the problem so we can offer the best solution for making your home more comfortable!