Monday, March 23, 2009

Layer Cake

A while back I wrote a blog on the occurrence of air stratification in homes. This is when warm and cold air layer in a room. Recently I came across a classic example of this during an energy audit. The infrared image at the right very distinctly shows how the air has layered in this room. The temperature difference between the ceiling and the floor, over 15 ยบ F.

The second infrared image shows the same occurrence in a connected room.

The reasons for this happening are for one physics and the other poor installation of the heating ducts.

In Connecticut we heat our homes most of the year. Consequently the heating registers should be located when at all possible in or near the floor.

In the two rooms pictured the heating registers were placed in or near the ceiling. The bright spot in the second image is the heating register.

With the idea to evenly heat the room the installers placed return air ducts near the floor thinking the warm air will be drawn down by the ducts. Not surprisingly that theory did not pan out. What's more if return ducts could be installed near the floor, they just as easily could have been made heating ducts. This was true in the second room as well. A storage room behind the wall affords ample space to install the registers down low.

This is a standard case of physics winning out over mechanics, but by applying a little more mechanics the problem can be resolved. In the room with the high ceiling putting in a ceiling fan will almost assuredly resolve the issue. Ceiling fans are a good energy efficient way to "homogenize" the room air. Running the fan will evenly warm the space causing the heating system to run less often.

The second half of the solution would be to relocate the registers. Doing this will be more costly and labor intense than putting in the fan, but will further achieve the desired benefit of a more evenly heated space.

Identifying a problem such as this one would be difficult without the aid of an infrared camera. However an HVAC installer should be cognizant of this effect when placing duct work. In the instances when ducts are unable to be ideally placed suggesting a ceiling fan be installed would be good advice.

Layer cake is tasty, but not on a wall.

James Quarello JRV Home Inspection Services, LLC

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