Whole house fan comparison

Daox · 06-08-11, 09:17 AM

Its a work in progress, but I started compiling a list of whole house fans and their specs and efficiency ratings in CFM/watt. Oddly enough, they're all over the board. The list is still growing, so I'll just post what I have so far. It appears the smaller Air King whole house window fan is really a great deal and a pretty efficient fan. The price varys widely as well. This is mainly due to some fans having active/insulated dampers and others just being a fan in a steel frame.

If anyone knows of any whole house fan manufacturers not on the list please let me know and I'll add their products.

RobertSmalls · 06-08-11, 05:34 PM

CFM/Watt is a fan efficacy quotient I've seen before, but it's a strange one. Flow * Pressure = Energy, so 1 CFM * 1 PSI = 3.25 Watt. If all the fans are tested with the same backpressure, then the efficacy rating corresponds to the thermodynamic efficiency of the fan as an air pump. However, this is a case where efficiency might not be a good measure of how cool it keeps you.

As for the dBA ratings... well, ask any SilentPCReview reader, and he'll point out that if you put the microphone near or far enough to the product, you can get any dBA rating you want. I really wish there were pervasive standards out there, such as all testing being done in a room of a certain geometry, with the microphone 1m away from the sound source.

EnergyStar has compiled a list of ventilating fans:

http://downloads.energystar.gov/bi/q..._prod_list.pdf

It's also available in .xls for your sorting & filtering convenience.

Daox · 06-09-11, 09:05 AM

Do you have any suggestions on how to rate the efficiency of the fans?

I looked at that list, and I see no whole house fans capable of exhausting the volumes of air I'm looking for (2000+ CFM).

Daox · 06-09-11, 09:19 AM

Hmm, here is what the EnergyStar website has to say about whole house fans:

Quote:

Is there an ENERGY STAR label for “whole-house” fans?

When used properly, “whole-house’ fans can be energy savers. However, EPA does not label these fans because all of the products perform about the same. Whole-house fans are mounted in the attic floor and pull cooler air from outside into the house through windows to lower the temperature of the house. Whole-house fans work well in climates where the days are hot but the evenings cool off quickly and there is low humidity (such as in the desert). In certain situations, whole-house fans can be used instead of air conditioning to cool off a house after a hot day. For example, when the temperature inside the house is 80-85 degrees and the temperature outside is 60-70 degrees after the sun goes down, the fan can be used to pull the cool, dry outdoor air in through the windows to quickly cool off the house instead of using the air conditioner. In a few minutes the house cools down and the fan can be turned off. The fan works quickly and uses much less energy than air conditioning.

So, does this mean all fan designs have roughly the same efficiency? Should I not worry about power consumption and just find one that blows enough air and be done with it? I know energystar isn't the end all in efficiency, but they have a decent handle on things. I still find it hard to believe all fans are basically the same.

MN Renovator · 06-12-11, 10:38 AM

Quote:

Originally Posted by RobertSmalls

CFM/Watt is a fan efficacy quotient I've seen before, but it's a strange one. Flow * Pressure = Energy, so 1 CFM * 1 PSI = 3.25 Watt. If all the fans are tested with the same backpressure, then the efficacy rating corresponds to the thermodynamic efficiency of the fan as an air pump. However, this is a case where efficiency might not be a good measure of how cool it keeps you.

Not quite. Unfortunately that isn't always the case. I have a furnace blower that I started to mess with, the more restricted its airflow(more pressure) the less amperage it draws. If there is no load on it, even on its low speed tap it will pull 6 amps and spin slowly but as soon as I cover half its output with cardboard the motors speeds up and pulls less than half the amperage. Not sure how that works but I took it into consideration when putting together my basement(cold) to upstairs(hot) exchanger, I had to determine the area to where the exponential amperage draw would sink to near the flatter edge but not restrict flow too much, works well now.

I'm not sure if blade fans like whole house fans have any design considerations or more efficient motors than others. I don't think that 200 or less watts is very much at all when comparing running an air conditioner instead. I had abandoned the thought of installing a whole house attic fan until I read that there are insulated ones in this thread but probably still won't because in the hot summer season when I would use it, the nights are very humid and I'd need to remove that humidity with the air conditioner during the day and use more overall power keeping it colder to make it more comfortable than if it were warmer with less humidity. ..stuff to consider depending on where you live.

06-08-11, 09:17 AM	#1
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Whole house fan comparison Its a work in progress, but I started compiling a list of whole house fans and their specs and efficiency ratings in CFM/watt. Oddly enough, they're all over the board. The list is still growing, so I'll just post what I have so far. It appears the smaller Air King whole house window fan is really a great deal and a pretty efficient fan. The price varys widely as well. This is mainly due to some fans having active/insulated dampers and others just being a fan in a steel frame. If anyone knows of any whole house fan manufacturers not on the list please let me know and I'll add their products. Attached Thumbnails __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

06-09-11, 09:05 AM	#3
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Do you have any suggestions on how to rate the efficiency of the fans? I looked at that list, and I see no whole house fans capable of exhausting the volumes of air I'm looking for (2000+ CFM). __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

06-08-11, 05:34 PM	#2
RobertSmalls Journeyman EcoRenovator Join Date: May 2009 Location: Buffalo, NY Posts: 344 Thanks: 3 Thanked 17 Times in 15 Posts	CFM/Watt is a fan efficacy quotient I've seen before, but it's a strange one. Flow * Pressure = Energy, so 1 CFM * 1 PSI = 3.25 Watt. If all the fans are tested with the same backpressure, then the efficacy rating corresponds to the thermodynamic efficiency of the fan as an air pump. However, this is a case where efficiency might not be a good measure of how cool it keeps you. As for the dBA ratings... well, ask any SilentPCReview reader, and he'll point out that if you put the microphone near or far enough to the product, you can get any dBA rating you want. I really wish there were pervasive standards out there, such as all testing being done in a room of a certain geometry, with the microphone 1m away from the sound source. EnergyStar has compiled a list of ventilating fans: http://downloads.energystar.gov/bi/q..._prod_list.pdf It's also available in .xls for your sorting & filtering convenience.