Cool my attic

[working4adollar]

Hey out there...

I need to cool my attic down. I live Tucson Arizona. The roof is basically flat, 2 side have about a 1 1/2 feet of space and approximately 3 1/2 feed in the middle. There is about 2200 square feet of attic, or about 5200 cubic feet. I have 3 vents to the outside. Each vent is 14 inches square) one vent on the north wall and 2 vents on the south wall). I calculate I will need to move about 1800 cubic of air per minute. The whole house fans I found at Home Depot move 3 times that amount. I would be pulling fresh ambient temperature (90'ish degrees) air in from the garage (not the house). and forcing the hot air out. Will this create an issue by pushing more air into the attic the can escape? I have thought of putting a speed control device on the fan to regulate the speed. which should reduce the CFM the fan puts out. The attic temps are easily exceeding 140 degrees. I am thinking Whole House Fan so I can mount the fan flat, it will have a flapper cover and I can put it on a plug rather then hard wire it in to the house.

Any ideas, comment would be appreciated.
Mike

 

[danski0224]

You will likely pull air out of the house.

Best solution will be spray foam.

 

[John McA]

What is the day to night temperature difference at your location?
What is your humidity percentage?
Do you have external shade on the structure? From which direction?
Good luck,
John McA

 

[65Goat]

^^^

 

[Walkers]

Attic fans have been done to death and provide very little relief. The reason is that the type of heat transfer that heats up your home through the roof is radiant. By definition, radiant heat transfers through the air, but does not heat up the air. So while you are removing air, you are doing nothing to stop the heat transfer. Your money would be better spent improving your insulation, or planting trees to shade your house.

 

[rharman]

Thoughts on these?

View attachment 1674039

^^^^ I have 3 of these ^^^^

2 for upstairs attic and 1 for downstairs. I assume they help (they surely have to) but can't quantify it as they were spec'd into our remodel (2nd story addition) by the architects.

 

[tool_scrounge]

Adding one gable vent fan to our house in So Cal made a huge difference in how hot it was in the house. Same result for my next door neighbor. If you are in an area prone to wild fires I have seen folks at a fire stat in-line with the power (shuts off the vent fan power if the temperature is too high)

 

[working4adollar]

John

What is the day to night temperature difference at your location?
What is your humidity percentage?
Do you have external shade on the structure? From which direction?
Good luck,
John McA

John
temp swings during the summer are between 30 and 40 degrees, humidity is very low... like single digit low. I do not have external shade. I have trees but they do not grow tall they just spread out. The two trees I have in the front of the house (which faces the west and the afternoon sun) are only 13 feet tall at best. I have trimmed them to try to get them to grow upward, and they will in time. I have planted trees at the back Of the house(which faces the rising sun) but they will take years to provide good shade. My main concern is getting the hot air out of the attic to help the longevity of my roof. I know I do want to create a negative pressure in the attic But what about a positive pressure?

 

[John McA]

Well. OP has a flat roof. And not as much volume to remove.
Honestly, and everywhere and micro climates are different:

A whole house with gable vents and lots of attic volume works well when you have a large diurnal swing from the day to night. Works all year for me and big close-able vents, with a bit of temp. monitoring in the attic, first and second floors. Use of windows at the appropriate locations and; a good talk with family on the air flow. AC not needed as a result for most conditions.
Good luck,
John McA

John

John
temp swings during the summer are between 30 and 40 degrees, humidity is very low... like single digit low. I do not have external shade. I have trees but they do not grow tall they just spread out. The two trees I have in the front of the house (which faces the west and the afternoon sun) are only 13 feet tall at best. I have trimmed them to try to get them to grow upward, and they will in time. I have planted trees at the back Of the house(which faces the rising sun) but they will take years to provide good shade. My main concern is getting the hot air out of the attic to help the longevity of my roof. I know I do want to create a negative pressure in the attic But what about a positive pressure?

Thanks for the almost immediate reply. I am going to suggest a an adiabatic cooler. If you are down in the 10% humidity range the cheapest way is to install that type of unit directly into the conditioned space, with a vent to your abysmally small attic volume. Risk? Throwing too much cold moist morning air volume up into that space can cause issues. You have likely seen the same units around your area. Some people refer them as swamp coolers. They are very good for low humid areas. And hugely simple. Have you checked in with your neighbors? I bet you have some cool times ahead.
I'm John.
What is your name BTW?
Good luck,
John McA

 

[John McA]

Like I said, if you got low humidity? SWAMP COOLER.

Anybody?

 

[gmcgeo]

If its a rubber roof, since you say flat. you can do an elastomeric coating.

Next is more insulation, fans, better insulation, better air flow.

 

[working4adollar]

Thanks John, My name is Mike.

Well. OP has a flat roof. And not as much volume to remove.
Honestly, and everywhere and micro climates are different:

A whole house with gable vents and lots of attic volume works well when you have a large diurnal swing from the day to night. Works all year for me and big close-able vents, with a bit of temp. monitoring in the attic, first and second floors. Use of windows at the appropriate locations and; a good talk with family on the air flow. AC not needed as a result for most conditions.
Good luck,
John McA

Thanks for the almost immediate reply. I am going to suggest a an adiabatic cooler. If you are down in the 10% humidity range the cheapest way is to install that type of unit directly into the conditioned space, with a vent to your abysmally small attic volume. Risk? Throwing too much cold moist morning air volume up into that space can cause issues. You have likely seen the same units around your area. Some people refer them as swamp coolers. They are very good for low humid areas. And hugely simple. Have you checked in with your neighbors? I bet you have some cool times ahead.
I'm John.
What is your name BTW?
Good luck,
John McA

 

[toplessHO]

Thoughts on these?
View attachment 1674039

make sure it has a firestat on it

 

[Copymutt]

I’m in that low double digit humidity and tried a swamp in my garage. It works brilliantly, except for rusting all my high carbon tools. Had to quit using it.

 

[Walkers]

I’m in that low double digit humidity and tried a swamp in my garage. It works brilliantly, except for rusting all my high carbon tools. Had to quit using it.

Hmmm, I’ve had a swamp in my shop for 20 years and have had no rust at all.

 

[Copymutt]

Dont quite have your triple digit temps. I see it hit the mid 90’s already in CC. Maybe that has a bearing on the rust. Always stay at buddies house on Cahava Ranch road for Good Guys.

 

[Walkers]

Dont quite have your triple digit temps. I see it hit the mid 90’s already in CC. Maybe that has a bearing on the rust. Always stay at buddies house on Cahava Ranch road for Good Guys.

Right down the road from me. Haven't been to good guys since 2019, maybe one day life will get back to normal...

 

[Denwood]

Do you have a pool? Solar pool heating effectively water cools your attic

 

[ybnormal]

anything you can do to shade your roof, like standoff roof panels, or as Denwood pointed out 'solar pool heating' . trees would work for shade but as pointed out, you live in Tucson

 

[luvtheheat]

I've lived in Tucson almost my entire life. House I grew up in had two of these. They did help. Was not a flat roof, though.

 

[Showkey]

Do you have a pool? Solar pool heating effectively water cools your attic

I suspect in Tucson………. OP needs a pool cooler