Attic fans?

[badgas]

Yowsa thats some juice, how many panels and which inverters are you looking at?

35 panasonic 400W panels EVPV400H and Enphase IQ8M 72-2 inverters

 

[TCHB]

Look up Fourier's Law. It is the calculations for heat transfer through a wall. One of the LARGEST integers in the formula is the Delta T value. The difference between the 2 different sides of the wall. This is ambient temp, AKA air temp. It is common on 100+ degree days for a standard attic to get up to 140+ degrees (I know, I used to have to work in them). If you have a interior space of 76, that gives you a multiplier of 64 degrees. Now, if you can install an attic fan in a properly ventilated attic and reduce that attic temperature down to 110 - 120, your multiplier has now dropped 20 to 30 degrees. That is a MASSIVE load difference.

All those scenarios for air leakage into the attic do not take into account insulation laying on top of those cracks and leaks. Will air still pass through, absolutely! But being it is impeded and there are other paths that are MUCH freer flowing, the air coming through those cracks will be miniscule at best.

Yes, thermal dynamics, ala convection, is a great way to naturally ventilate an attic. Assuming the ventilation openings and outlets are all in the correct locations and un-impeded. Adding a miniscule amp draw (usually less than that of an incandescent light bulb) electric motor to assist in the process can help a poorly designed attic work better.

Also, heat moves from high to low. Hot AIR rises. Heat doesn't have a direction besides high to low. Materials' thermal conductivity has more impedance to heat transferring into a structure than any sort of convection out of the interior of the space.

If the HVAC system is pressurizing the attic space, then you have FAR larger fish to fry than concerning yourself over the tiny amp draw of an attic fan.

What HVAC guy doesn't say windows play a huge role? They play a MASSIVE role. Specially depending on their orientation (North, West, East, South). I could do heat load calcs to illustrate, but just don't quite have the time ATM.

My parents replaced all their old single pan double hung original 1970's wood frame windows with new double pane vinyl windows and had a LARGE electricity reduction (I cant remember what it was they told me). The house is A LOT more comfortable inside as well.

I can tell you first hand with all the air conditioner techs up in the attic it is a lot cooler. It stays about the same temperature as outside. The techs loved it.

 

[Nanu/Nanu]

I've never been a big fan of attics

 

[Taboma]

Yowsa thats some juice, how many panels and which inverters are you looking at?

KWH or KW of output ? 18,000 kwH can be roughly achieved with 3,000 KW output (Average) in 6 hours. Is the "H" intentionally included or is it to be ignored in this case ?

 

[Uncle Dave]

KWH or KW of output ? 18,000 kwH can be roughly achieved with 3,000 KW output (Average) in 6 hours. Is the "H" intentionally included or is it to be ignored in this case ?

Its one thing to have 3KW, something total different to have 3000KW - people often misquote and add the h or leave it out

Badgas is going to have 14KW of total panel production on its face -pretty substantive.
How many KWh he gets is up to his roof and shading and location.

 

[Uncle Dave]

From this old house

One reason that attic fans are inefficient is that they rely on the existing attic vents (at the soffits, ridge, or gables) to make up the air they exhaust. Usually, these attic vents are not designed for this purpose, and they may not be able to supply enough replacement air. That can put the attic at a lower pressure than the upper floor of the house, which sucks conditioned air into the attic through holes for recessed lights, attic stairs, whole-house fans, and the like.

Conditioned air can also be sucked directly out of unsealed ducts in the attic. In this situation, adding attic fans can cost you more cooling dollars than not having a fan.


H

Don’t Let Your Attic Suck - Power Attic Ventilators Are a Bad Idea - Energy Vanguard

Trade shows can be both educational and infuriating, and there’s one product I see at a lot of trade shows that fits easily into the latter category – power attic ventilators. The variety of this device that’s been popular lately…

www.energyvanguard.com

Also from This Old House.

In warm weather, the surface of your roof can get as hot as 160°, heating up the attic space and making rooms directly below the attic uncomfortably warm. This puts a big load on your air conditioning system, causing spikes in your electric bill. One way to minimize this problem is to install an attic fan. This active ventilation system is inexpensive and easy to install. An attic fan will turn on automatically when the attic reaches a preset temperature. The fan is typically mounted behind a gable-end vent, but other types are available that exhaust hot air through a roof vent.

All About Attics

Attics are the space between the roof and the ceiling of the highest floor of the house. They’re usually full of insulation, and sometimes heating or air conditioning equipment as well.

www.thisoldhouse.com

Seems to me the message here isnt to avoid them, but make sure if you put one in that you're sure it has enough flow.

 

[Taboma]

Its one thing to have 3KW, something total different to have 3000KW - people often misquote and add the h or leave it out

Badgas is going to have 14KW of total panel production on its face -pretty substantive.
How many KWh he gets is up to his roof and shading and location.

Certainly, KW and KWH being two different units of measure. KW being a measure of power consumed or produced, KWH a measure of how much is consumed or produced in one hour, or hours if plural. A substantial difference as is a 1 KW or KWH vs 1,000 KW or KWH.
Thanks for the translation

 

[badgas]

Its one thing to have 3KW, something total different to have 3000KW - people often misquote and add the h or leave it out

Badgas is going to have 14KW of total panel production on its face -pretty substantive.
How many KWh he gets is up to his roof and shading and location.

Correct

They claim/estiamte with my roof that the 14KW system will generate 19,395kWh. This is an estimate and they also say they under estimate by 8% to be on the safe side.

Who knows ? it could be sales BS but I will be pissed if I go down this rabbit hole and the thing produces way under what they estimated.

 

[Uncle Dave]

Correct

They claim/estiamte with my roof that the 14KW system will generate 19,395kWh. This is an estimate and they also say they under estimate by 8% to be on the safe side.

Who knows ? it could be sales BS but I will be pissed if I go down this rabbit hole and the thing produces way under what they estimated.

You'll prob be ok but asking on of our peeps here to take a look is a good idea.

 

[NicPaus]

How much to windows play into home cooling ?

Window companies say it's a big deal HVAC companies say windows do very little.

Any real word examples of how much good windows help ?

I'm in So Cal never ever run the heater but the AC runds from July-Sept.

My River mobile it made a 20 degree difference. But the old were majority louvered. I switched to dual pane low E and put the silver sun block in all the ones with direct sunlight.

 

[Uncle Dave]

Over the weekend I ordered a high volume window fan. I’m 5 miles from the beach so I should be able to cool off my second story every evening when the outside temp drops and then run it in the morning right before the sun comes up. Curious to see how effective it is.

Which one did you get?
Im looking at the king air for my garage.
I used push pull box fans for years to great effect - well my whole life really before spending the money on the WHF.

 

[Justfishing]

Yowsa thats some juice, how many panels and which inverters are you looking

Also from This Old House.

In warm weather, the surface of your roof can get as hot as 160°, heating up the attic space and making rooms directly below the attic uncomfortably warm. This puts a big load on your air conditioning system, causing spikes in your electric bill. One way to minimize this problem is to install an attic fan. This active ventilation system is inexpensive and easy to install. An attic fan will turn on automatically when the attic reaches a preset temperature. The fan is typically mounted behind a gable-end vent, but other types are available that exhaust hot air through a roof vent.

All About Attics

Attics are the space between the roof and the ceiling of the highest floor of the house. They’re usually full of insulation, and sometimes heating or air conditioning equipment as well.

www.thisoldhouse.com

Seems to me the message here isnt to avoid them, but make sure if you put one in that you're sure it has enough flow.

Also from This Old House.

In warm weather, the surface of your roof can get as hot as 160°, heating up the attic space and making rooms directly below the attic uncomfortably warm. This puts a big load on your air conditioning system, causing spikes in your electric bill. One way to minimize this problem is to install an attic fan. This active ventilation system is inexpensive and easy to install. An attic fan will turn on automatically when the attic reaches a preset temperature. The fan is typically mounted behind a gable-end vent, but other types are available that exhaust hot air through a roof vent.

All About Attics

Attics are the space between the roof and the ceiling of the highest floor of the house. They’re usually full of insulation, and sometimes heating or air conditioning equipment as well.

www.thisoldhouse.com

Seems to me the message here isnt to avoid them, but make sure if you put one in that you're sure it has enough flow.

I will listen to this guy. He is one of the top building science and energy efficiency experts in the US. Pay attention to about the 2:00 minute mark. Listen to what he says about power attic vents. We are talking attic fans and not whole house fans.

This video goes over the proper way to vent an attic. Listen to what he says about radon, pesticides and mold. If think you are smarter than Joe call him up and tell him he is wrong.

 

[Uncle Dave]

I will listen to this guy. He is one of the top building science and energy efficiency experts in the US. Pay attention to about the 2:00 minute mark. Listen to what he says about power attic vents. We are talking attic fans and not whole house fans.

This video goes over the proper way to vent an attic. Listen to what he says about radon, pesticides and mold. If think you are smarter than Joe call him up and tell him he is wrong.

I listened to this several times. Ive actually heard this guy before

He describes what you want- you want lots of holes at the bottom and a few at the top.

Then he said what you don't want - a lot of holes on top and a few holes down low because then your attic would suck and what would make that worse is to install an attic fan.

Im not doing what hes saying not to do - I have tons of vents on the bottom - all the way across the bottom on both sides.
Im also not sucking so hard I'm depressurizing the attic and sucking the air out of the house.

I have a sealed door at the far end of the attic and it opens with utter ease with the fan on, and when I walk around in the attic with an incense stick I dont even see air move until Im a few feet from the running fan.

The tidbit I did get out of the rewatch of this was that my new (owens corning) cool roof is going to be very effective.

 

[Justfishing]

What is you cool new roof

 

[Uncle Dave]

What is you cool new roof

I'm re roofing the house with an Owens Corning cool roof. The shingles have high reflectance.

I did the same exact roof at the LA house prior to moving so the renter got all the benefit.

Hopefully it will keep the second floor at least a few degrees cooler - Im in the time of year where its 100 for a month straight.

I appreciate your posts and input.

 

[badgas]

I will listen to this guy. He is one of the top building science and energy efficiency experts in the US. Pay attention to about the 2:00 minute mark. Listen to what he says about power attic vents. We are talking attic fans and not whole house fans.

This video goes over the proper way to vent an attic. Listen to what he says about radon, pesticides and mold. If think you are smarter than Joe call him up and tell him he is wrong.

I did not watch the entire video but I did run upstairs and count canned lights when he talked about holes in the ceiling.

I counted 34

 

[4Waters]

I will listen to this guy. He is one of the top building science and energy efficiency experts in the US. Pay attention to about the 2:00 minute mark. Listen to what he says about power attic vents. We are talking attic fans and not whole house fans.

This video goes over the proper way to vent an attic. Listen to what he says about radon, pesticides and mold. If think you are smarter than Joe call him up and tell him he is wrong.

So you're saying attic fans work now

 

[Flying_Lavey]

I will listen to this guy. He is one of the top building science and energy efficiency experts in the US. Pay attention to about the 2:00 minute mark. Listen to what he says about power attic vents. We are talking attic fans and not whole house fans.

This video goes over the proper way to vent an attic. Listen to what he says about radon, pesticides and mold. If think you are smarter than Joe call him up and tell him he is wrong.

How old is that video? The information he is using regarding the A/C is not near accurate for today's standards. Again, this is all with the assumption that there is not enough make-up air coming into the attic.

And BTW, I'd the convection is working correctly, even that process puts the attic into a slightly negative pressure situation or else it won't draw air into the eve vents.

So, like I have said from the beginning, with proper and sufficient make-up air vents in the attic mechanical ventilation can be extremely effective and can reduce the heat load on the interior envelope.

 

[SHOCKtheMONKEY]

I will listen to this guy. He is one of the top building science and energy efficiency experts in the US. Pay attention to about the 2:00 minute mark. Listen to what he says about power attic vents. We are talking attic fans and not whole house fans.

This video goes over the proper way to vent an attic. Listen to what he says about radon, pesticides and mold. If think you are smarter than Joe call him up and tell him he is wrong.

Phone number?

 

[Justfishing]

Phone number?

Its on his web site. Buildingscience.com. and the L is silent.

 

[Justfishing]

How old is that video? The information he is using regarding the A/C is not near accurate for today's standards. Again, this is all with the assumption that there is not enough make-up air coming into the attic.

And BTW, I'd the convection is working correctly, even that process puts the attic into a slightly negative pressure situation or else it won't draw air into the eve vents.

So, like I have said from the beginning, with proper and sufficient make-up air vents in the attic mechanical ventilation can be extremely effective and can reduce the heat load on the interior envelope.

It has nothing to do with the makeup air. Air moves or leaks because of a pressure differential. To suck air in you have to create a differential. The air will come through any opening if there is a differential. Yes more air will come in from vents.

Also i never said it will not lower the attic temp. The more you want to lower it the more negative pressure you must create. Which in turn means a bigger fan and more energy. It also means more air leakage from inside.

You will never see an attic fan in an energy eiificient house because its not needed. The insulation is to keep the heat out.

Air leakage is a super big penalty. To illustrate there is a product called areo barrier that helps air seals homes. A builder in phoenix wanted to sell net zero homes. A code home would have needed a $50k solar array. The builder worked hard and could only get to a hers50 score. That would still need a $30k array. With aero barrier they reduced the ach from 1.4 to .6 and can now get by with just 8 panels versus 30. That is how much air leakage means to an already well built home. In the ops case i am sure the home is much leakier and the fan would contribute to more air from the home.

Air leaks can come from places you wouldnt think it can. Radon travels into the house from air coming from underground. How does that happen.

Everyone has talked about attic air temp. No one has said anything about radiant heat. That is what is by far the bigger load.

The op i assume want lower not higher bills and wants better comfort. Address the issues correctly.

 

[Justfishing]

So you're saying attic fans work now

He clearly said attic fans were bad. I have never said they wont reduce temp. I have said they will likely increase your utility bill and are not the solution

 

[4Waters]

He clearly said attic fans were bad. I have never said they wont reduce temp. I have said they will likely increase your utility bill and are not the solution

They absolutely do affect your bill, they reduce it, especially the solar fans. He's wrong, as long as your attic is set up properly they work amazingly, you should put one in, you would be shocked

 

[Activated]

Thought I clicked on the Speed Car thread for a minute.

 

[Flying_Lavey]

It has nothing to do with the makeup air. Air moves or leaks because of a pressure differential. To suck air in you have to create a differential. The air will come through any opening if there is a differential. Yes more air will come in from vents.

Also i never said it will not lower the attic temp. The more you want to lower it the more negative pressure you must create. Which in turn means a bigger fan and more energy. It also means more air leakage from inside.

You will never see an attic fan in an energy eiificient house because its not needed. The insulation is to keep the heat out.

Air leakage is a super big penalty. To illustrate there is a product called areo barrier that helps air seals homes. A builder in phoenix wanted to sell net zero homes. A code home would have needed a $50k solar array. The builder worked hard and could only get to a hers50 score. That would still need a $30k array. With aero barrier they reduced the ach from 1.4 to .6 and can now get by with just 8 panels versus 30. That is how much air leakage means to an already well built home. In the ops case i am sure the home is much leakier and the fan would contribute to more air from the home.

Air leaks can come from places you wouldnt think it can. Radon travels into the house from air coming from underground. How does that happen.

Everyone has talked about attic air temp. No one has said anything about radiant heat. That is what is by far the bigger load.

The op i assume want lower not higher bills and wants better comfort. Address the issues correctly.

Oh please continue to attempt to lecture me in airflow. This is classic! Please tell me again how airflow works.

 

[Uncle Dave]

Now come on!! Quit using math and logic here!!

Turns out the HVI has the numbers .

I need approx 775 net inches of soffit ventilation.

Did the math and it turns out I have over 1K so Im good on the numbers.

After spending a ton of time absorbing multiple white papers there are lots of ways to do attic fans wrong, and only a few ways to do them right starting with ventilation and tempered expectations as to what you are going to get, all to say the WHF has far better ROI.

How Much Ventilation Do I Need?

How Much Ventilation Do I Need? HVI's ventilation guidelines. Ventilation products have differing capacities for moving air, making it important to ensure the product being selected has ample capacity for the applicatio

www.hvi.org

 

[RogerThat99]

Over the weekend I ordered a high volume window fan. I’m 5 miles from the beach so I should be able to cool off my second story every evening when the outside temp drops and then run it in the morning right before the sun comes up. Curious to see how effective it is.

I have used a window fan in our bedroom for 10 years or more. I am on my second fan because I wore the first one out.

It works great to cool the besroom when it is nice outside. For me, I found it is better to have it blow cool air in, rather than try to blow the warm air out.

I put it on High in the evening, then turn ti low when we go to bed.

 

[Uncle Dave]

I have used a window fan in our bedroom for 10 years or more. I am on my second fan because I wore the first one out.

It works great to cool the besroom when it is nice outside. For me, I found it is better to have it blow cool air in, rather than try to blow the warm air out.

I put it on High in the evening, then turn ti low when we go to bed.

" window fans" were the fancy version.
As a kid, we put box fans in windows in the summer and it works really well for a single room. a lil humid but you had zero Air con anyway as the parents were too cheap to run the AC unless it was a million degrees with 100% humidity. After a month of that I couldn't sleep without a box fan running.

In a single story house blowing in works better than trying to suck air through a house by blowing out, but in a two story house you get a chimney effect that helps move air through when you blow out the top and the ultimate fan setup also has a pusher fan in the room you are in.

The WHF works better than box fans but you still have to manage the flow the way you want it with strategic window opening.

 

[dezertrider]

There are some cool industry improvements coming soon to the attic fan world. These are great as long as its cooler outside then inside. Most of them run on temperature so they are great fo rthe Cali market not so much the AZ market.

 

[Ducksquasher]

Wha

There are some cool industry improvements coming soon to the attic fan world. These are great as long as its cooler outside then inside. Most of them run on temperature so they are great fo rthe Cali market not so much the AZ market.

What are the improvements?

Thanks!

 

[dezertrider]

Wha
What are the improvements?

Thanks!

They are going to be smarter and more functional in all climates. The info I got was confidential but they will be public in a bout 6 months

 

[Ducksquasher]

They are going to be smarter and more functional in all climates. The info I got was confidential but they will be public in a bout 6 months

Thanks!

 

[Orange Juice]

I can tell you first hand with all the air conditioner techs up in the attic it is a lot cooler. It stays about the same temperature as outside. The techs loved it.

I usually turn on the bathroom fans