Thread: Cooling A Room
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Unread 24-05-2007, 12:11
Mike Bortfeldt Mike Bortfeldt is offline
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Re: Cooling A Room

Pavan,

Two years ago I had similar problems with both the heating & cooling in my house. In the summertime, the AC would cool the 1st floor fine, but the 2nd floor (where the bedrooms are) was always much warmer. The same was true in the winter (only reversed). One difference from your problem was if I had a fan in the bedroom circulating the air, then the AC would actually cool the room fine. It stayed hot when the only air circulation was the furnace blower. After doing a little research, I made the following changes (I'll include the heating changes in case anyone is interested). I’m not sure if any of these are applicable to you, but hopefully you might get some ideas.

1) The ductwork in my house mainly runs through (what should be) an unheated/cooled area of the house (basement) so I insulated all the supply ducting in this area. I also located and fixed any leaks within the ductwork itself in these areas. This all by itself resulted in a noticeable change in the basement temperature as I was not accidentally heating it in winter or cooling it in summer as much.

2) I read online (I can't at the moment find the website) that air conditioning requires more airflow than heating for it to work efficiently. If yours is an older house that was not originally designed for air conditioning, it may have grilles (vents) with slits that are too small and restrict airflow too much. I replaced all the room vents with new ones with larger openings that also allowed me to direct the air toward the center of the room rather than having the vent scatter the air off to the sides or straight up. This change eliminated the need for a separate fan in the bedrooms to circulate the air, as the furnace blower now was able to circulate the air within the room without any assistance. It also help direct the air out into the room when the vent was under a desk or otherwise somewhat obstructed. This does result in more “drafts” when the blower is running, but overall it is worth it in my opinion.

3) Originally all the return air vents were at the baseboard level. This worked fine for heating, but efficient air conditioning requires the return vents to be mounted near the ceiling to allow the warmer air to removed from the room. I added additional return vents at ceiling level above the existing ones using the wall cavity between the studs as the ductwork. I also replaced all the return vents with ones that can be closed, so that in the summer time, the upper ones are open, and in the winter, the lower ones are.

4) As others have mentioned, adjust the dampers on all the individual ducts to even out the heating/cooling throughout the house.

5) Keep a clean filter in the unit to keep the airflow as high as possible.

6) For heating, my furnace has a delay between shutting off the natural gas and when the blower shuts down. This was originally set to 30 seconds. I increased this to 150 seconds to transfer more of the remaining heat from the heat exchanger and ductwork into the living areas of the house (unfortunately this doesn’t work when in the cooling mode)

7) Replaced the thermostat with one that allowed me to set deadband for turning the heating/cooling on/off. I increased this value, which reduced the cycling of the furnace.

8) Add plastic to some of the larger windows (or ones that don't seal as well as they should). Hot air rises, so to some extent it doesn't matter where the hot air enters the house, it will work it's way up.

9) If you have an attic above your room, make sure you have sufficient insulation. Add a temperature-controlled fan to the attic area to remove the hot air. It's not uncommon to have an attic that is 20-30+ degrees hotter than the outside temperature.

10) Restricted the air return on the vents closest to the furnace to try to draw more air from the rooms farther away.

These changes significantly increased the efficiency of the heating/cooling. Before, on a hot summer day, the AC would not be able to keep up and the house would slowly get warmer (the whole system is probably a little undersized), now not only does it keep up, but it can cool it down. It also reduced energy consumption by over 20% as well as making the entire house more comfortable.

Mike