# Air conditioning and skylights



## 480sparky (Feb 1, 2009)

Satisfy my curiosity:

I have a vaulted ceiling in my kitchen, with a skylight in it. The skylight has a vent in it. It's nice to be able to vent the warm air in the house at night and let mother nature cool things down inside during summer nights.

I know to keep it closed when the furnace is running, but is it better to open it when the air is running, or close it?


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## Leo G (May 12, 2005)

If your system is set up correctly with output at the ceiling level and the returns at the floor then the skylight should remain closed. Also depends on the height of the ceiling too. If it is higher than 10' you could leave it open for a period of time to let the heat vent. But the currents will continue after the heat is gone and drain the cool air too.


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## griz (Nov 26, 2009)

It is designed to be a closed system to "condition" the interior by cooling the air & lowering the humidity. If you allow the ambient air to enter, it is presumably considerably warmer & has a higher humidity level than desired thereby defeating your original intent to cool the interior air.


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## Mike Finley (Apr 28, 2004)

Leo G said:


> If your system is set up correctly with output at the ceiling level and the returns at the floor then the skylight should remain closed. Also depends on the height of the ceiling too. If it is higher than 10' you could leave it open for a period of time to let the heat vent. But the currents will continue after the heat is gone and drain the cool air too.


I think Leo has this one right.

We do the same thing with a whole house fan on the 2nd floor. Turbo boost cooling down the house by turning it on if the A/C has been off, expelling the hotter air out of the house is going to cool faster then mixing that hot air in the A/C system. However, once you blast it out of the house the advantages are over and you should close it down.


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## Tom Struble (Mar 2, 2007)

its like opening your car windows after its been sitting in the sun


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## beenthere (Mar 5, 2009)

Opening it. Pulls in unconditioned air from from outside through the normal cracks in your home. Causing a higher humidity in the house.

The A/C will dehumidify the air in your house much better and faster if you keep it closed.


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## flashheatingand (May 3, 2008)

beenthere said:


> Opening it. Pulls in unconditioned air from from outside through the normal cracks in your home. Causing a higher humidity in the house.
> 
> The A/C will dehumidify the air in your house much better and faster if you keep it closed.


You are big on de-humidification. At what temp/ humidity level do people start to turn on the a/c in your neck of the woods? 

Here, we have dry weather, so, generally, we leave windows open until the odt gets above 93 or so.

My answer would be that it's ok to leave the sky light open as that would be a good way to expel the hot air. We have a lot of new homes around here (2-15 years old) Without a lot of tree shade. A big problem is that people keep windows closed, and since these places are so air tight, there isn't anyplace for the heat to go. Keep the doors and windows open, and the heat load goes down drastically (opinion).


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## beenthere (Mar 5, 2009)

Here. Some people let their A/C run when ever the house temp gets above 72. And if its 72 outside, they still let the A/C run.
Others won't run it until the outdoor temp reaches 80.

In apartment buildings. Some use it when its 65 outside.

If you have a skylight. Open it and measure the CFM going out of it.


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## flashheatingand (May 3, 2008)

Wow!!! 80 degrees? Thats a big difference.


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## beenthere (Mar 5, 2009)

We got all kinds of people in this area. Some like it hot, others like it cold.


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## Baltar (May 21, 2010)

If you open the skylight you are losing house pressure/depressurizing it. In theory that can affect the static pressure in your ductwork and airflow. A furnace and ductwork are designed to work in a closed house. We have lots of cheapskates here who like to camp in front of the ole electric meter and have heart palpitations if it starts spinnin too fast.:w00t:

If your RH outside is less than 60% I would do it for a short time. Otherwise you are sucking in humid air and paying too remove the moisture.


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## Tom Struble (Mar 2, 2007)

why is it that things that seem to make perfect sense are usually wrong?:blink:


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## Baltar (May 21, 2010)

If you talk to enough smart people and not think too much of your "intelligence" you usually get the right answer. I stopped making assumptions years ago.:thumbup:


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## flashheatingand (May 3, 2008)

Isn't there something to be said of "pure fresh" air? I just can't imagine living with windows closed and keeping the home sealed during the summer. Humidity or not.


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## Leo G (May 12, 2005)

Fresh air is over rated when it is 90º and a dew point of 70+


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## beenthere (Mar 5, 2009)

flashheatingand said:


> Isn't there something to be said of "pure fresh" air? I just can't imagine living with windows closed and keeping the home sealed during the summer. Humidity or not.


Pure fresh air?

Ain't no such thing as pure fresh air today.

ERVs/HRVs are made for people that want fresh air. They eliminate some of the energy increase the fresh air adds to the home use.


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## AustinDB (Sep 11, 2006)

flashheatingand said:


> Isn't there something to be said of "pure fresh" air? I just can't imagine living with windows closed and keeping the home sealed during the summer. Humidity or not.


I thought you were just being a smartazz so I checked the weather for Boise tomorrow-98 degree high


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## flashheatingand (May 3, 2008)

It will be hot from about 1:00-6:30. Then, we will need to have the a/c on. But by about 7:45, we just need to open things up.


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## Tom Struble (Mar 2, 2007)

i think he is still a smart azz:shifty:


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## flashheatingand (May 3, 2008)

Hey, I can't help it if you mansy pansies can't handle a little humidity. Look on the bright side, it keeps your skin looking quite alabaster.


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