Attic Ventilation

[cruzinZ]

I need some help of the more experienced members in attic ventilation. I live in a desert climate in California's central valley. Typical temperatures during June, July, August & early September are in excess of 100 degrees. We've had times of 100 to 110+ degree days for 5-6 weeks straight in the past.

This weekend's project was installing 2" styrofoam insulation on the garage door. I ended up blocking out the windows in the top bay & turned my garage into a cave. In doing this I've drastically reduced the daytime temperature in the garage. This little project has now morphed into a lighting problem that will need to be taken care of at another time.

Back on track. I'm looking to reduce the attic temperature in both attic spaces. First one is above the garage, attached 3 car tandem garage, the second one is above the house. Also looking to add insulation and would like some recommendations on brands here as well.

I'm looking for 3 fans & need some input on brands/models. For the attic above the garage this space is ~250 sq ft. It is not very large but gets the most direct sun exposure and the most heat in the afternoons. Its also responsible for increasing the temperature of the master bedroom closet 20º & Master Bedroom temps ~5º. I will be insulating this area as it currently does not have any insulation. Typical track home and building to the minimum standard they can get away with.

Second fan is for the attic space above the house. 1860 sq ft 2 story. East/West facing home.

Third fan is to fit in a vent cut-out in the garage that is 13"X17.5". I'm planning on using this one to help reduce garage temperatures and currently having a hard time finding one that will fit.

I would like the garage attic space & garage fan to be controlled by a thermostat. I would like the attic space above the house to be controlled both manually and with a thermostat. I have a mechanical & electrical aptitude and will be able to figure out the electrical part on my own.

What brands would you guys recommend for these 3 fan's? I'm looking for something that is solid & built out of metal that will give me a useful working life. Not looking for a big box store fan with bearings that will fail within the first year. Next is budget. After the wife getting her "backyard remodel" $10K & this summer's vacation I'm looking for middle of the road quality fans.

Next year I'll be looking into a whole house fan and more fun in the attic above the house with insulation. Thinking about renting a foam gun and shooting up under the roof trusses.

Any help with brand's models would be greatly appreciated.

 

[pseudorealityx]

I need some help of the more experienced members in attic ventilation. I live in a desert climate in California's central valley. Typical temperatures during June, July, August & early September are in excess of 100 degrees. We've had times of 100 to 110+ degree days for 5-6 weeks straight in the past.

This weekend's project was installing 2" styrofoam insulation on the garage door. I ended up blocking out the windows in the top bay & turned my garage into a cave. In doing this I've drastically reduced the daytime temperature in the garage. This little project has now morphed into a lighting problem that will need to be taken care of at another time.

Back on track. I'm looking to reduce the attic temperature in both attic spaces. First one is above the garage, attached 3 car tandem garage, the second one is above the house. Also looking to add insulation and would like some recommendations on brands here as well.

I'm looking for 3 fans & need some input on brands/models. For the attic above the garage this space is ~250 sq ft. It is not very large but gets the most direct sun exposure and the most heat in the afternoons. Its also responsible for increasing the temperature of the master bedroom closet 20º & Master Bedroom temps ~5º. I will be insulating this area as it currently does not have any insulation. Typical track home and building to the minimum standard they can get away with.

Second fan is for the attic space above the house. 1860 sq ft 2 story. East/West facing home.

Third fan is to fit in a vent cut-out in the garage that is 13"X17.5". I'm planning on using this one to help reduce garage temperatures and currently having a hard time finding one that will fit.

I would like the garage attic space & garage fan to be controlled by a thermostat. I would like the attic space above the house to be controlled both manually and with a thermostat. I have a mechanical & electrical aptitude and will be able to figure out the electrical part on my own.

What brands would you guys recommend for these 3 fan's? I'm looking for something that is solid & built out of metal that will give me a useful working life. Not looking for a big box store fan with bearings that will fail within the first year. Next is budget. After the wife getting her "backyard remodel" $10K & this summer's vacation I'm looking for middle of the road quality fans.

Next year I'll be looking into a whole house fan and more fun in the attic above the house with insulation. Thinking about renting a foam gun and shooting up under the roof trusses.

Any help with brand's models would be greatly appreciated.

Greenheck, Cook, PennBarry, etc will all be good quality commercial grade brands. Broan would be another choice.

 

[BadgerBoilerMN]

I do ACCA approved load calculations meaning I have to plug in construction components to provide loads and size equipment for HVAC.

I would start with insulation before installing fans that are not cost effective. If you are in a dry desert climate, an evaporative cooler would be in order. Solar gain through window nearly always creates the highest cooling load.

Look to proper passive roof ventilation before burning electricity.

 

[Toymeister]

Use a capacitor start fan for good CFM, chinese so not the absolute best like this one http://www.amazon.com/gp/product/B001V5J1XA/?tag=atomicindus08-20 or a us made one that is a DC brushless model like this one http://www.quietcoolfan.com/afges1500.html

I have both, the expensive one is used where I can't easily replace it

 

[rodder98]

I would also definitely add a foil radiant barrier in the attic area to reflect the heat back up away from the ceiling. atticfoil.com has some good info about this. I bought some for our house in central Florida and it made a big difference.

 

[mx842]

Adding fans to your attic space is usually not the best idea. What happens when you run these fans is that along with a little of the hot air you are sucking your nice air conditioned air out of your living area too. Forget about how hot the attic space is unless your wife makes you sleep up there. It's summer, it's supposed to be hot. You are far better off sealing off any cracks and crevices that you find, ceiling lights, receptacles, switch plates, around windows and doors and ADD insulation.

Sealing up your living space will keep you cooler in the summer, warmer in the winter and also help keep your home cleaner and the air quality better. Before I spent money on all those fans I would and what it would cost to run them from now on I would buy what spray insulation I could afford and spray the whole attic. Either take up what insulation is in there if you can and spraying the ceiling to seal off everything. Or you could just spray the underside of the roof and seal off the whole attic.

someone mentioned the radiant foil barrier. That works pretty good but it is expensive also and wont seal up the attic the way foam does. Both have their advantages and disadvantages and if either is too cost restrictive just add more batt insulation or spray in some spray in when you have a few bucks laying around.

 

[BadgerBoilerMN]

Rational thought is so refreshing.

A little known fact is that cellulose can be blown over fiberglass to increase its extreme weather performance. In sub-zero weather for instance, the typical batt or blown glass can lose 50% its R-value due mostly to convection. As little as 6" of cellulose can mitigate this failing.

 

[pseudorealityx]

And while the attic is supposed to be hot, there's a big difference between a 110 degree attic and a 130 degree attic.

And if you properly vent the attic along the soffits and/or gables, I don't think you're really going to exhaust much air out of your house, unless you've got a terribly rickety, poorly fitting attic hatch/door. And the 10? cfm you're losing out of the house is going to be countered by lowering the ceiling/attic surface temp by 10-15 degrees over the entire radiant surface.

Adding insulation is certainly step 1. But ventilating the attic isn't a bad thing, be it natural or active.

 

[mx842]

And while the attic is supposed to be hot, there's a big difference between a 110 degree attic and a 130 degree attic.

And if you properly vent the attic along the soffits and/or gables, I don't think you're really going to exhaust much air out of your house, unless you've got a terribly rickety, poorly fitting attic hatch/door. And the 10? cfm you're losing out of the house is going to be countered by lowering the ceiling/attic surface temp by 10-15 degrees over the entire radiant surface.

Adding insulation is certainly step 1. But ventilating the attic isn't a bad thing, be it natural or active.

The problem is that those fans are not going to remove enough heat to make a difference When it's 100 degrees outside or even 90 the amount of heat the roof decking is able to absorb will is going to pretty much remain constant as long at the radiant energy from the sun is shining on it. The only way you could prevent that would be to install some sort of radiant barrier so that the heat either bounces off the roof before it is allowed to heat up the roof system. That could be some of the new energy saver type roofing materials or a light colored energy saver metal roofing system. There are also radiant barrier panels or rolls that you install inside the attic under the roof deck that some say work pretty well but anything that really works will be fairly expensive. If I was going to spend my money it would be on more or better insulation not a fan that's going to cost money to run, do little good an possibly someday short out and burn my house down. Of course that's just my opinion and you know what they say about those things.

 

[pseudorealityx]

I'm definitely NOT arguing against insulation. Step 1 should be more and better insulation. I'm just saying that step 2 could be ventilation, be it natural or mechanical.

As to how much heat is rejected out of one of these fans... I just looked up the specs on a standard Dayton fan out of Grainger.

1600 cfm @ 0" SP
295 watts consumed

0" SP is a joke... so let's just use 1200 cfm as some sort of actual flow. Figure you've got a 90 degree day, and a 120 degree attic space.

1200 cfm * 30 degree delta T * 1.08 = 38880 btu, a bit more than 3 tons. I'd say that's something.

And let's assume that you've only got outrageous attic temps for 4 months a year.

295 watts * 12 hrs/day * * 30 days/month * 4 months/year * ~$0.10/kWhr * 1kw/1000 w= ~$43/year

As far as things that may short out and burn houses down... I dunno about you, but I have lots of electric things in my house. Suit yourself if you're afraid of them.

 

[earlthegoat2]

My house is uninsulated and I am keeping it that way for now. However I did do a total refit of continuous soffit vents and a ridge vent and that helps a great deal down here in the dirty south.

 

[Toymeister]

Adding fans to your attic space is usually not the best idea. What happens when you run these fans is that along with a little of the hot air you are sucking your nice air conditioned air out of your living area too. Forget about how hot the attic space is unless your wife makes you sleep up there. It's summer, it's supposed to be hot. You are far better off sealing off any cracks and crevices that you find, ceiling lights, receptacles, switch plates, around windows and doors and ADD insulation.

Sealing up your living space will keep you cooler in the summer, warmer in the winter and also help keep your home cleaner and the air quality better. Before I spent money on all those fans I would and what it would cost to run them from now on I would buy what spray insulation I could afford and spray the whole attic. Either take up what insulation is in there if you can and spraying the ceiling to seal off everything. Or you could just spray the underside of the roof and seal off the whole attic.

someone mentioned the radiant foil barrier. That works pretty good but it is expensive also and wont seal up the attic the way foam does. Both have their advantages and disadvantages and if either is too cost restrictive just add more batt insulation or spray in some spray in when you have a few bucks laying around.

Seriously, are we in alternate universe and only meet up on the 'net where the same laws of physics do not apply? In my world I vent a hot attic to keep the ceiling of my home cooler for the same reason I insulate the attic, the less the delta in temp from my attic to my house the better. In my world foil based insulation for a DIY is fairly inexpensive both attic fan and foil are cheaper than spray in insulation.

An attic fan does not **** air from my home when there are vents in the soffit of my attic. Air is lazy and it takes the path of least resistance which is not through the ceiling.

Edit to add spray in insulation is cheaper if MX is talking about a can or two of spray insulaltion, but not cheaper than an entire attic of spray insulation