Air fans and efficiency

curtis73 wrote: Who cares if it draws air from the eaves or the ridge, or anywhere else for that matter. It will be theoretically replacing the entire volume of the attic's air three times every minute.

I think you are confusing us. You started talking about using a fan to cool the house which is a whole house fan as SVreX stated. But you keep bring up the volume of the attic which is importeant to an attic vent fan but somewhat immaterial to a whole house fan.

I grew up in a house with a whole house fan about 20 miles from where you live. The house is a single story and the fan is placed in the ceiling of the hallway leading to the bedrooms from the rest of the house. The fan is 36" in diameter and is run by a 1/2 horse electric motor. It is a high volume rather than a high speed fan. It has enough suction to lift a single sheet of news print off the floor under it and pull it thru the fan.

It did require a sizeable number of soffit and roof vents to keep from overpressureizing the attic.

From the pics of your house you could probably mount one in the ceiling of the upstairs hall near the stairway. You could put some vents in the gable ends of the attic to allow the air to exhaust.

Why would I attempt to use a 1500 CFM squirrel cage that draws 4 amps to do a job it was not designed for, when a standard 24" whole house fan draws 2.3A and moves 4500 CFM's?

Home Depot Whole House fan

There are NO critical structural framing components in the gable wall of your roof, regardless of whether it is 80 years old or 800 years old. They are ALL non-load bearing.

SVreX wrote: Why would I attempt to use a 1500 CFM squirrel cage that draws 4 amps to do a job it was not designed for, when a standard 24" whole house fan draws 2.3A and moves 4500 CFM's? Home Depot Whole House fan

First of all, I was using hypothetical numbers which is why I asked the question in the first place. I'm asking which type of fan typically moves the most CFMs per watt. All you've done so far is tell me that my idea sucks but haven't given me any information on why. If i wanted to go out and buy a random commercially-offered fan without doing any research, I wouldn't have asked the question.

If you have a better idea, put it out there. Don't just say I suck and then not tell me why. I asked the question hoping for answers, not flames. We're not talking about creating massive pressure variants or sucking the dirt through my basement floor, we're talking about mainly unobstructed airflow.

... and the studs in the end of the gable are pretty critical for the end of the roof. Randomly altering them is not something I am excited to do if I can achieve the same (or more) airflow with a different style of fan.

Hal wrote: I think you are confusing us. You started talking about using a fan to cool the house which is a whole house fan as SVreX stated. But you keep bring up the volume of the attic which is importeant to an attic vent fan but somewhat immaterial to a whole house fan.

Quite possible... however his original criticism of my squirrel cage fan was that it draws air from the sides (eaves) instead linearly like a regular fan. I was merely pointing out that with the volume I plan it doesn't matter.

I grew up in a house with a whole house fan about 20 miles from where you live. The house is a single story and the fan is placed in the ceiling of the hallway leading to the bedrooms from the rest of the house. It did require a sizeable number of soffit and roof vents to keep from overpressureizing the attic. From the pics of your house you could probably mount one in the ceiling of the upstairs hall near the stairway. You could put some vents in the gable ends of the attic to allow the air to exhaust.

My attic currently has end vents on the left and right walls. They aren't enough to be fully sufficient, but they are enough that I could run a 2-speed fan on low without opening any ceiling vents and not collapse the attic :) Soffits are modestly vented, but since the interior ceilings are slanted to match the roof everywhere except in the dormers, who knows how much venting is actually taking place.

If I get time tomorrow I'll post a drawing of what I'm thinking.

curtis73 wrote: ... and the studs in the end of the gable are pretty critical for the end of the roof.

Sorry...they are not.

I've built over 500 houses. Worked on hundreds of older ones. Gable jacks are NOT structural. Ever. Especially in a house with as small a span as your rafters have.

You are going to do it your own way. I give. You win. There is no question you are asking in this thread that Google can't answer, or that you don't already have your own answer.

I recommend you give it a shot in whatever manner you see fit. Let us know when you've got some experiences that we might learn from.

SVreX wrote: You are going to do it your own way. I give. You win. There is no question you are asking in this thread that Google can't answer, or that you don't already have your own answer.

Google has TONS of answers that are sponsored by millions of Lemmings who followed advice from people like you who just bought the commercially-offered solution. The reason I'm asking this here is because the title of our beloved forum includes the word GRASSROOTS. If I wanted to follow the herd, I would have swiped my credit card for whatever the salesman offered.

What I'm asking basically boils down to; "what car offers the most bang for the buck?" You are suggesting that I give into the hype and buy the most expensive, retail-priced, lowest-bid fan and hack up my attic. The whole reason I asked is so I don't have to do that.

This is Grassroots Motorsports forum. If you have Lemming-based retail-priced advice to offer, go somewhere else. This is a forum in which we cast our own control arm bushings from different durometer material based on our driving style. This is the forum where we discuss the shortcomings of Ford's I-beam front suspension and use our knowledge to improve it. We talk about putting 5.0L Fords in Miatas. If I wanted corporate retail responses, I would have asked this question on the Home Depot forums.

SVreX wrote: I've built over 500 houses. Worked on hundreds of older ones. Gable jacks are NOT structural. Ever. Especially in a house with as small a span as your rafters have.

Did you build those houses in Pittsburgh in 1937? Did you then come back and examine how your heavy tongue-and-groove roof held up after 75 years of soil migration? This house has moved a full 19 inches downhill since it was built according to original surveys. Hacking into a stud wall in the attic is not just a cut-and-paste operation. It requires more engineering than your flat, sandy Georgia experience can handle. I've been a contractor in PA, CA, IN, MT, TX, and FL. Don't tell me that gable stands are not structural until you've cut into one in a PA house and had 1/4 of the roof come down on your head.

In reply to mguar:

You know, there are a ton of people that don't like the dry air coming out of an AC, right? I live in Florida, and I truly hate that I don't live in an old enough house to have been built without central AC in mind. I far prefer opening windows to firing up the AC, and it has absolutely nothing to do with spending money on it.

I like having the option of fan vs. A/C, because this pudgy old dude LIKES that cool dry air at times. A whole house fan is on my list of possible upgrades. For instance, tonight would be perfect: low 60's and about 60% humidity. Low speed with the windows open about 3"...

Curmudgeon wrote: I like having the option of fan vs. A/C, because this pudgy old dude LIKES that cool dry air at times. A whole house fan is on my list of possible upgrades. For instance, tonight would be perfect: low 60's and about 60% humidity. Low speed with the windows open about 3"...

We thinks alike

I don't quite get you. You ask for advice and then poopoo it when it isn't what you want to hear. Your not going to grassroots a better whole house fan than a whole house fan. People have done the engineering and leg work for you and determined the best way to do it is a large diameter traditional blade fan. There isn't some conspiracy by comercial home improvement to keep you from getting the $5 fan that is free to operate and majically cools your house. I applaud your efforts to go green and would just look for a used whole house fan. Or if attic fan is what you need a used one of those. If you really want to build it yourself there is no reason you can't use a squirel cage fan you will have some crazy dicting to do but you can use a used furnace fan for the fan. I dont design fans and cannot tell you if squirrel cage fans are somehow more efficient but my gut tells me they are used because of compactness for a given CFM first and any efficiency gains second.

nocones wrote: I don't quite get you. You ask for advice and then poopoo it when it isn't what you want to hear.

I disagree. I asked the question, and I've been poopoo'd without a reason. Everyone keeps saying that "the commercially-offered solution must be the best one." But no one has said why despite my multiple requests. If I wanted to get the standard commercially-offered option, I wouldn't have asked on GRM. Understand? I just feel like I'm being really clear but speaking a different language. Everyone has said numerous times that I'm stupid and I should just get the Home Depot fan for X-hundred dollars, but no one has answered my original question of why.

Your not going to grassroots a better whole house fan than a whole house fan.

I guess I was hoping someone would be able to explain the "why" part. I simply wanted to know general CFM/watt. I thought it was a simple question like asking about HP/weight of midsize FWD cars.

People have done the engineering and leg work for you and determined the best way to do it is a large diameter traditional blade fan. There isn't some conspiracy

Conspiracy? no. However, (speaking of FWD cars), it could just be that blade fans are cheaper to make and make larger profits for the company. Just saying.

If you really want to build it yourself there is no reason you can't use a squirel cage fan you will have some crazy dicting to do but you can use a used furnace fan for the fan.

There won't be any ducting. Here is what I was thinking in this quick sketch. Obviously the ceiling vent would be something that could open and close - either passively or actively) Regardless of what kind of fan there is (a big bladed fan that requires some re-framing - OR - a squirrel cage fan that doesn't) it seems like airflow is airflow. Why would one fan design be better than another? That's the question I'm trying to answer.

In the interest of clarity, I will re-state my original question: I want to install an attic fan as house ventilation. My question is about CFM per watt basically. I know some designs are more effective at creating pressure (like a vacuum cleaner) and others are better at creating flow (like a squirrel-cage type). I'm basically looking for something that moves large CFM with the least amount of wattage Period. Done. I asked which fan to use, then I asked why. I've heard that I'm stupid for not following the herd, but I haven't heard the why part yet.

Alright I did some googling on your behalf..

First your sketch won't work (or at least will be really inefficient) unless your attic is 100% sealed so the only air supply that the fan can get is from inside your house. I'll leave it to our more construction minded members who would know exactly why that's a bad idea but every house I've seen has sofit and ridge vents that would probably make that fan move very minimal air through that square without ducting forcing that fan to get all of it's air from the house interior.

Ok on to efficiency. It looks like per the following link normal blade type whole house fans draw ~500 watts to move 6000 cfm of air. That's 83 watts/1000cfm

http://www.homedepot.com/h_d1/N-5yc1v/R-202067896/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=whole+house+fan&storeId=10051

Now according to our friends at UCDavis at typical very efficient squirrel cage furnace fan/blower motor draws ~170watts/1000cfm.

http://eec.ucdavis.edu/ACEEE/2002/pdfs/panel01/21_394.pdf

Go to any factory, dairy farm, attic fan, comercial whole house fan or any situation where you want to move a lot of air and you will find various diameters of standard blade fans. I suspect this is because when it comes down to it this is the most efficient way to move air and it appears that the actual efficiency data backs this up. The only places I've really seen squirrel cage type fans are places where CFM for a given space and low noise is important.

UCDavis has this to say about these fans

UCDavis said: As discussed in Sachs (2001), most residential HVAC equipment uses sheet metal centrifugal fans with large numbers of thin, forward-curved impeller blades. These are compact, inexpensive, and easily manufactured. They easily meet static pressure specifications. However, conventional fan designs have relatively low peak efficiency, less than 70% (shaft to air). In addition, most designs do not maintain their efficiency across a very large flow ratio (varying cfm). With ECPMs, manufacturers can consider other impeller designs.

Now interestingly enough some of the most efficient appearing whole house fans seem to be DC plastic bladed types. To really bring this GRM I think we all know of a source for various diameters of 12V DC blade fans. They also are normally shrouded to pull from a square opening. I think you may find that your best source for hyper efficient fans are as new as possible radiator fans. You will have to do an AC/DC conversion to run these but I'd think if your looking at various alternate power sources these typically run DC, and if it's only an on demand useage the conversion shouldn't be to bad. You could even charge a battery off peak if you get scalled electrial rates for least cost.

Why would you need any framing changes, again? Seems like a box built with whatever fan on one side could easily have one or more openings on another side that would exit your attic between stud.

Were it me I would pick a nice size standard $80 window from a big box store that fits between studs and frame up a hole in the end of the attic that it would drop into. That way the hole is easily and cleanly sealed up later. Then build a simple box on the inside and attach whatever fan you want to. Use screws, and if whatever you use doesn't work as desired then you're a 1/2 hr project away from swapping to whatever else you want to try.

Then you can tell us how well it worked and end the speculation.

Now I can tell you from personal observation that of the couple dozen furnace blowers my Dad turned into shop fans moved only a small fraction of the air of any of the whole-house fans I've experienced. I can sit in front of a furnace fan and enjoy the breeze, but walking under a whole house fan in the ceiling of a hallway will suck a hat off your head.

oldopelguy wrote: Why would you need any framing changes, again? Seems like a box built with whatever fan on one side could easily have one or more openings on another side that would exit your attic between stud.

I thought about that, but was irrationally concerned with the amount of air that might be blocked by a stud in the middle of things. I started thinking about ducting it to openings that were of equal or greater surface area and it got too complicated.

Now I can tell you from personal observation that of the couple dozen furnace blowers my Dad turned into shop fans moved only a small fraction of the air of any of the whole-house fans I've experienced. I can sit in front of a furnace fan and enjoy the breeze, but walking under a whole house fan in the ceiling of a hallway will suck a hat off your head.

I have had the opposite experience. I had an A/C blower in my garage that would blow the hat off my head, and it was a 240v fan that I was running on only 120v. It drew 2.4A as measured with the AC current calipers on my multimeter.

In reply to nocones:

You rock. That is exactly the kind of factual info I was seeking but couldn't find. I must not have put the right keywords in the googles.

Thank you for the info.

nocones wrote: Go to any factory, dairy farm, attic fan, comercial whole house fan or any situation where you want to move a lot of air and you will find various diameters of standard blade fans.

Which could be because they are the most efficient, or it could mean that they are the cheapest... or that government dairy farming tax breaks pay for the electricity anyway so who cares... or that a corporate pencil pusher decided that factories should have blade fans.... etc.

I'm simply asking a question, and after a few dozen posts you have actually given me some stuff to consider. Thanks.

See, where we live, houses don't have basements. The water table it too high. The coolest air available here is ambient outside air. I hate the dry air we get from having to run the AC constantly. If this house were built without AC in mind, it would be well insulated, have a wraparound veranda, and it would have an attic that is well insulated.

If sun light doesn't shine on your exterior walls and you have a large, well ventilated and insulated attic, you can get away without AC, even here in Florida. It's a shame a swamp cooler doesn't work here.

IIRC, Chuck Harder of For The People network radio program designed and built a house around an 'air shaft' in the center of the house w/ a whole house bladed fan in the attic. I believe the floor plan was semi-open so the shaft would normally (fan off) act like a chimney venting as hot air naturally rises. On high heat days the fan would operate pulling air from lower floors, windows were adjusted to trim air flow through rooms.

The house was in Florida so no basement. The goal was to reduce AC costs. My limited googles didn't return anything but the info may be out there.

Sounded like a cool idea anyway.

curtis73 wrote: Don't tell me that gable stands are not structural until you've cut into one in a PA house and had 1/4 of the roof come down on your head.

The reason I CAN say that because I HAVE cut into hundreds of houses in PA and DID NOT have 1/4 of the roof come down on my head. I lived there for 10 years.

I was licensed in PA long before I was in GA. Mostly older historic structures and timber framing. I currently hold a national license, so I am licensed in all 50 states. The rest of your assumptions and accusations about me are also false, but they don't hurt me. You saying things that are untrue about me won't make them true.

If you have been a contractor in 6 states (as you claim) and have experienced 1/4 of the roof come down on your head by cutting a gable jack, please consider a different field. You are a disaster waiting to happen if your lack of understanding about structures is that severe. But I suspect that was nothing more than an exaggeration for dramatic effect.

BTW- cutting a gable jack in the average GA house DOES create a structural defect (by cutting a pre-engineered truss), unlike cutting a gable jack in a stick built (or timber built) structure in the average PA house.

Regarding grassroots... you are not being grassroots, you are being argumentative and stubborn. Big difference. Grassroots would say, "Hey guys, I got this squirrel cage fan for free and installed it as an attic fan- I'm really excited, check it out!", to which I would have responded, "That's cool!". Your question was not designed to gain information or share experience, it was designed to piss people off and try to prove your manhood by belittling other people with more experience and knowledge than yourself. I spent 7 years working in appropriate technology with Habitat for Humanity- that essentially means my job was identifying and understanding grassroots technologies for construction in hundreds of locations around the world. It's an area I have more experience than most folks. Sorry if that makes you feel threatened. Guess I can't help someone who doesn't actually want to be helped.

I have no need to go further in this pissing match with you. I'm done.

I was serious when I suggested you try it, and share real info when you learn it. I would be genuinely interested.

One more thing...

No one called you stupid. Especially me. You are not a stupid man. You are an extremely intelligent person with a great capacity for expansive creative thought.

Y'all are a bunch of big dumb stupid poopieheads.

Way back in the Dark Ages of the 1960's there was a bait store not far from our house. This place was built in probably the 1920's and had had an A/C system retrofitted which, as I understand/remember, was basically a cooling tower outside maybe 20 feet tall. There was an exchanger inside the building with a fan behind it, a pump circulated water through the exchanger and then to the top of the tower, where it cascaded down these slats which IIRC looked like clapboards set about half an inch apart. There was a fan at the top which I believe blew air down into the tower, I remember the thing splattered water all over the place. When the water hit the collection pool at the bottom, it was sucked into the exchanger inside and went for a ride all over again. From my knowledge of refrigeration, I don't think this thing would be very efficient but I could be wrong. Any of you bright boys know if it's even possible? I know it's done to cool nuclear reactors, big buildings etc but could it work for a house? And yeah I know you'd have to keep adding water due to evaporation...

It works well in hot dry climates (very popular in western australia), but not in hot humid climates.