Whole house fan issues

Reply

  #1  
Old 06-12-13, 09:57 AM
H
Member
Thread Starter
Join Date: Jun 2013
Location: USA
Posts: 2
Received 0 Votes on 0 Posts
Whole house fan issues

I purchased a a belt drive 36" fan, 9700cfm's on high. It runs for about 3-4 minutes then shuts off and re-starts itself in about 5 mins. The manufacturer claims I don't have enough attic ventilation and the fan is overheating because of that.

My house specs: 2500 total sq. feet. The attic is 988 sq feet. I have 27 feet of ridge vent, and 92 linear feet of 12 inch soffit, and 3 10-inch square roof vents.

I just can't believe this isn't enough ventilation. I'd sure appreciate some help.
 
  #2  
Old 06-12-13, 10:08 AM
G
Member
Join Date: Nov 2007
Location: MI
Posts: 2,634
Received 1 Vote on 1 Post
Can't be that hot in your MD attic this time of year. Should be an easy matter to verify the motor is too hot by touching it but my bet is you have a bad motor.
 
  #3  
Old 06-12-13, 11:49 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,524
Received 37 Votes on 34 Posts
Somebody may need to check my numbers, but I estimate your total NFA (net free area) to be around 12 ft², which is double what that size attic needs. That's 10% NFA for soffit and 90% for ridge and roof vents. Assuming all is not blocked, then that part is good.

Where the problem comes in is the size of the fan vs the attic. If your 988 ft² attic has a 4,000 ft³ volume, then that fan will exhaust all the attic air in less than 30 seconds. Wind speed at all intakes would have to approach 15 MPH. That would suck an attic hatch open let alone pull air through all ceiling leaks.

Just playing with the numbers so we will need to run them again to be sure I haven't slipped somewhere, I do that occasionally, but 9700 CFM does seem like overkill.

Anyone else take a shot at the NFA and air flow?

Bud
 
  #4  
Old 06-12-13, 12:19 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 36 Votes on 28 Posts
Bud, it isn't an "attic" fan, it is a whole house fan. Probably is mounted in the ceiling and has an automatic shutter that opens when running. It is to exhaust air from the entire house (windows open) and it is exhausting into the attic. While the attic venting IS sufficient for natural draft venting of the attic it can't take the huge airflow without pressurizing the attic.

Husker, the motor on your fan requires airflow over the motor for cooling. Without sufficient airflow the motor will indeed overheat. The existing vents in your attic are simply insufficient to allow the proper airflow.
 
  #5  
Old 06-12-13, 01:15 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,524
Received 37 Votes on 34 Posts
You are correct Furd, my quick read. But the exhaust flow remains high and that size fan, if it had enough opening, house and attic, would exchange all the house air in 2 minutes. That's 30 times per hour.

The other concern with a whole house fan would be any combustion appliances, heat or hot water. If any are naturally drafted they will fail for sure.

Thanks Furd, I knew someone would watch after me).

Bud
 
  #6  
Old 06-12-13, 01:57 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 36 Votes on 28 Posts
Several years ago we had some unusually hot weather in my area. I used a 20-inch box fan as a whole house fan, sticking it in the kitchen window (on the east side of the house) and then opening windows on the west side. The fan was rated at about 1,000 CFM on high which would mean about five air changes per hour. I would run it on medium or slow so figure less than four ac/hr. It would definitely cool the house overnight, sometimes way too much. It also brought in a huge amount of dirt that was just floating in the air outside. I can't imagine what kind of a tornado Husker must have blowing through his house.
 
  #7  
Old 06-12-13, 04:42 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,524
Received 37 Votes on 34 Posts
That's probably what is happening, either the windows are not open or the total restriction is limiting that tornado, which is why the motor is overheating. We also have a window mount three speed fan and you have to get up at night to shut it off. I guess that is the nature of cool evenings. 46° the other night so we still have the furnace going on occasions.

Bud
 
  #8  
Old 06-12-13, 07:18 PM
Andrew's Avatar
Member
Join Date: Apr 2003
Location: USA
Posts: 1,017
Received 14 Votes on 10 Posts
Have you checked the amp draw on the motor & comparing it to the nameplate amperage? This would be the best way to see if the motor is being overloaded.
Andy
 
  #9  
Old 06-12-13, 09:11 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 36 Votes on 28 Posts
I don't think the fan motor is overloaded, just the opposite. There is not enough air going over the motor to adequately cool the motor.
 
  #10  
Old 06-12-13, 09:41 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,398
Received 1,399 Votes on 1,296 Posts
I find it hard to believe that the motor is shutting down on high heat in 3-4 minutes due to lack of air flow.

It almost sounds like the motor is undersized for the job.
 
  #11  
Old 06-12-13, 09:49 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 36 Votes on 28 Posts
Fan motors are usually designated as "air over" and require the airstream of the fan passing over to remove the heat. An air over motor without sufficient airflow could very well trip the embedded thermal cut out in three or four minutes of operation if there was not sufficient airflow.
 
  #12  
Old 06-13-13, 05:22 AM
airman.1994's Avatar
Member
Join Date: Dec 2005
Location: VA
Posts: 5,795
Received 8 Votes on 8 Posts
Im going to take another road! Your in MD! These fans are not recommended in a green grass area which you are in because of the humidity.
 
  #13  
Old 06-13-13, 12:16 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 36 Votes on 28 Posts
Airman is correct that use of a whole house fan will bring in a lot of moisture during its run time. That may not be a severe problem if the house does not also have air conditioning but if it does it WILL be a severe problem.

Something for all of us to consider, husker logged off one minute after posting and hasn't logged back in since. I know it has only been one day but if it were me I would be checking in as often as possible looking for answers.
 
  #14  
Old 06-14-13, 06:28 AM
H
Member
Thread Starter
Join Date: Jun 2013
Location: USA
Posts: 2
Received 0 Votes on 0 Posts
I appreciate everyone's comments. As I've been checking and double checking things for the past few days. The fan will not run on low, even when I reverse the wiring to the switch (bad switch vs. bad motor). Low still doesn't run, the fan shuts off. In answer to a couple of questions posted, yes, the motor is hot after the 3-4 minutes. And I have had most of the windows in the house open and it doesn't seem to matter. I really think there is a problem with the motor.
 
  #15  
Old 06-14-13, 07:38 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,524
Received 37 Votes on 34 Posts
Hi husher,
The calculations I did on NFA for the attic venting assume that all of that vent area is not blocked by something. Ridge vents are sometimes covered where the roofer forgot to cut the underlayment away. Soffits can be filled with insulation. Where you opened the windows in the house, that would be one side of the air flow. If you are confident or have confirmed the attic side is fine then the fan should be working.

I'm not sure what wiring changes you made when you reversed the wiring to the switch, but you need to be confident all is wired correctly and the fan is rotating in the correct direction.

Bud
 
  #16  
Old 06-14-13, 09:15 AM
G
Member
Join Date: Nov 2007
Location: MI
Posts: 2,634
Received 1 Vote on 1 Post
Originally Posted by airman.1994

Im going to take another road! Your in MD! These fans are not recommended in a green grass area which you are in because of the humidity.
Who has been put in the position whether or not to recommend a simple fan? My guess would be a HVAC salesman.

Everyone's comfort level varies--all more reason I would never be so presumptuous as to recommend against the use of a whole-house fan. In areas where AC is only needed a few days each year a fan offers a very cost-effective alternative.
 
  #17  
Old 06-14-13, 09:53 AM
airman.1994's Avatar
Member
Join Date: Dec 2005
Location: VA
Posts: 5,795
Received 8 Votes on 8 Posts
Very true! But MD will need AC more than just a few days a year! Unless you are used to working in a steel mill.
 
  #18  
Old 06-20-13, 01:24 AM
R
Member
Join Date: Jun 2013
Location: USA
Posts: 1
Received 0 Votes on 0 Posts
Our whole house fan has been in about 22 years and has worked great.
It's a 30", 2 speed belt drive, 4 blade unit in a 1400 sq ft house and it's only run on low speed, 1/9th hp. The motor finally went out a few months ago. The symptoms were running for about 10 minutes, shutting off and restarting about 15-20 minutes later. One of the motor bearings was worn out and the subsequent heat generated destroyed the rubber bearing mounts, too. The fan blade bearings and drive belt were in surprisingly good condition. After replacing the motor it was still shutting off occasionally. Loosening the drive belt helped a lot, but still shut off. The fan manufacturer told me they are running the newer motors at higher temps for more efficiency (not sure how that works). I strapped a thermometer to the casing and it's running around 103 deg. After looking things over a bit more it looks like the starting capacitor is blocking airflow thru the motor because it's mounted on the end of the casing. I relocated the capacitor to the side of the motor mounting bracket and it hasn't shut off in 2 weeks. I've been using it everyday for the last 6 weeks on low. The motor temps are still around 103 deg, so I'm thinking moving the capacitor out of the hot airflow helped somehow.
 
  #19  
Old 06-20-13, 01:40 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,398
Received 1,399 Votes on 1,296 Posts
I've had a 36" Chelsea belt driven fan in the gable end of my attic for 40 years. The motor is just starting to give me trouble. Front bearing is noisy and the centrifugal switch is pitted pretty bad.

I have an electronic timer on it and make sure it turns off way before dew point hits to keep the damp air out. I've saved a lot of money using the fan instead of the AC.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: