Cooling problem on the second floor


Old 03-30-03, 06:57 AM
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Cooling problem on the second floor

I have two story colonial home that is 55 years old. My furnace and A/C are in basement and I have 4" ducts. I have new 92% efficient furnace and A/C. However, second floor is not called enough on summer. At 100F outside my second floor is maximum cooled down to 78F or 79F while the first floor is called to 73F or 74F. The contractor that installed furnace and A/C told me that the problem is 4" ducts (he said new homes have 6" ducts). My friends recently bought a new home and they are having the similar problems with cooling the second floor although maybe not as much as I am. What can be other sources of problem (preferably from moist affective not less)? I checked that my artic insulation is very old and not in good order. Should I close more duct registers on the first floor to force more air to the second floor? Although my contractor said not to do it as it may damage A/C.
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Old 03-30-03, 07:07 AM
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First of all, make sure your a/c blower is on high speed. Then make sure the air filter is clean. That should insure that you are getting all the air flow you can possibly get. Close a register or two on the first floor, preferably the ones closest to the thermostat. And run the blower all the time to mix air (albeit slowly) throughout the entire house.

What returns do you have from the second floor? Are they high on the wall?
That is a key defect in homes where a/c was added after the system was installed as heat-only. In a/c season, you need all the hot air from the ceiling of the highest room in the house to get back to the unit and get cooled to make the whole house comfortable.

No magic pill here but you can probably improve comfort by tweaking and tuning a little.
Old 03-30-03, 08:27 AM
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I am not sure how I can adjust a/c blower speed. I clean air filter every three weeks or so. I also don't understand what it means "to run blower all the time". I am very bad in a/c or heating yet. My thermostat has fan settings that can be set to On. Off and Auto. If On is set fan works only when a/c or heater works, Auto mode makes fan work all the time.

I have five returns on the first floor (in every room except kitchen and bathroom) and two return registers on the second floor. They are in the hall at the ceiling level (highest possible). I also had two more return registers on the second floor hall near the floor level which apparently came from the same duct. However the contractor told me that I could close those ones that I did and now I have only two returns near the ceiling.

I also need to emphasize that at summer time my a/c works almost all the time . It can never cool the first floor below 71F in hot day.

I would like to know what I can really do to improve cooling of the second floor. My first floor and my basement are cooled fine.
Old 03-30-03, 12:54 PM
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Dear agalkin--

Running the blower all the time means setting the thermostat fan switch so that air is coming out of the ducts all the time instead of only coming out when the furnace is heating or a/c is cooling. You said your when your thermostat fan switch is in the "auto" position the fan runs all the time and when it is in the "on" position it works only when the a/c or heater works. This should not be since thermostats are designed to run the system fan continuously in the ''on'' position and not the ''auto". Are you sure you didn't misspeak how it works?

Next, like KField said "Close a register or two on the first floor, preferably the ones closest to the thermostat" If your basement and 1st floor are ok, begin closing down the lower floor registers a little at a time to see if the upstairs situation improves. Shut the registers that blow out only halfway to start. Set your thermostat fan switch so the fan runs all the time and allow a few hours between changes to see if the upstairs is doing better.

Also, open up all the return registers upstairs. Don't shut the registers off all the way as your system cannot work properly if it can't "breathe" (think of an a/c and heating system as breathing in through your mouth and out through your can see what happens when you shut any of the openings and better understand the principle)

Hope this helps...let us know
Old 04-01-03, 08:33 AM
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When the ducting was installed in this house, was it designed to both heat AND cool, or was the system designed to just heat the house, and it has since been retrofitted to also cool?

Heating is best accomplished by delivering the heat at the floor level. AC is best accomplished by delivering the cooling at the ceiling level.

In the winter, the first floor will require a greater heat input than the upper floor in part due to the heat rising from the first floor to the second. In the summer, the top floor will require the greater cooling input due in part to the cool air falling to the lower level.

The "best" heating and cooling systems are seperate systems, b/c the dynamics of heating and cooling are different.

A forced air system that uses the same duct work to both heat AND cool is a compromise. Such a compromise may lower the effectiveness and comfort of a combined system.

Comfort is compromised even further if duct work designed to heat your house is now also used to cool it.

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