question about cooling my house

[Günter VögelBerg]

My house is a single floor with a finished but largely unused attic space with an open stairway up. Including the attic space the house is about 1200 sf. I have central air. In the roof there are two skiylights that can open. Would it be advantageous when cooling the house to open the skilights slightly to let warm air escape?

Edit: should add that humidity is not a concern. I live in a dry climate.

[Mike Nolan]

It depends. Put a thermometer in the attic and outside in the shade. If it usually hotter inside the attic then opening the skylight would help. There are attic fans that turn on when it is hotter in the attic than outside. I would look into installing one. It would be a lot more effective than opening a skylight.

[Edward Dyas]

Yes it would but I would forget about it until rain started coming through the ceiling.

[Alan Rutherford]

Any air that escapes through the skylights will be replaced with air from outside the house so probably not. If the outside air is better than what's inside the house then yes but that's probably not the case if you are running the AC.

If you put a door at the top of the stairway and provide for ventilation into the attic from outside, that would be different.

[Günter VögelBerg]

Any air that escapes through the skylights will be replaced with air from outside the house so probably not. If the outside air is better than what's inside the house then yes but that's probably not the case if you are running the AC.

If you put a door at the top of the stairway and provide for ventilation into the attic from outside, that would be different.


This is what I would actually like to do...eventually. It will be a bigger project than just adding a door. The air up there is not generally hotter than outside., so that reasoning makes sense.

[Alan Caro]

Guenter VoegelBerg,

If the house has a pitched roof, perhaps consider building a quite good-sized fan into each vertical end wall so that one fan pulls air into the attic space and at the other end that fan pushes it out. The type of fan to use has louvers, so when hey are not operating, the rain and/or the old air does not come in.

The fans can be controlled by a thermostat- when the attic becomes 25 or 28C+ for example, the fans go on. When they shut off the louvers close.

Does the attic have insulation in the floor or the rafters? That is important to minimize the heat transfer.

Also, it's important for the Winter that the stairway to the attic can be closed off effectively to prevent the heated air escaping as it rises. In the summer, the it can be open and that will help lower the temperature on the ground floor as it will rise and the fans will push it out.

Alan

[Bill Dufour]

I do not think this is what I would call an attic. I think this is a finished loft space open to the lower floor. So loud industrial attic fans are out. If i cools off at night a whole house fan can help.
What is the floor like upstairs? consider adding in floor insulation if the floor is carpeted or similar that can be pulled back. I would suggest blown in cellulose as it is cheap and will help quiet noise as well.
Bill D.

[Günter VögelBerg]

I suppose it would be more accurate to call it a loft. It actually is fairly well insulated in the roof, at least judging by relatively low snow melt. I am actually planning on completely gutting the space and turning it into an office--that is probably a project for 2021. When I do that I will reconfigure the stairs so I can install a door.

[Kev Williams]

If the central air is running it's counterproductive to open a window or other vent. The AC is cooling the INSIDE air, therefore you want as little as possible of that cooled air to escape, nor the hot air finding its way in to replace it.

For those running a swamp (evaporative) cooler, the opposite is true because they pump in and cool large amounts of OUTSIDE air, and you need to leave a window or two open so the warm air its replacing can escape. And that open window should be as far from the cooler as possible, so the airflow path moves thru as much of the house as possible. (Ideally is to crack open a window in every room so the cooled air will find its way to all of them)

Anyway, keep the place closed up if the central air is running. Venting later in the day when it's not running IS a great idea..

[Nicholas Lawrence]

I would not call that an attic either. Attic to me means unfinished space.

What kind of solar gain do you get from the skylights? Keeping the curtains closed helps a lot with cooling during the worst part of the summer here.

[Jim Matthews]

Venting the upper reach of the house will create a "stack effect" like a chimney. Even if the opening is quite small, this will exhaust conditioned air and place additional load on your HVAC.

Passive methods as you suggest work well when temperatures drop overnight - conditioned air works as a "closed loop" where a given volume is tempered.

Short version : AC on? Windows closed.