Replies

1. 
   WorkshopJon | Jul 24, 2005 07:07am | #1

   Derf,

   Many, many years (20?) ago I had a girlfriend who's parent's house had one.  In like five minutes you could get the house down from like 95F to 70F.  WAAAAY faster than AC.  Just open all the lower windows and turn it on.  That's all I know about them.

   WSJ

1. 
   BillHartmann | Jul 24, 2005 02:48pm | #3

   You are talking about a whole house fan that sucks air out of the house into the attic and hopefully then out through attic vents.He is talking a relatively small fan that whose purpose is to ventilate attic and has no connect to the house (except in the leaks as 4lorn1 mentioned).

1. 
   edwardh1 | Jul 24, 2005 03:52pm | #4

   according to florida power and light, attic fans do not save energy. do a web searchuse natural vents and buy insulation which works in winter too

2. 
   4Lorn1 | Jul 24, 2005 01:02pm | #2

   Sometimes an attic exhaust fan is the only practical way to go. A lack of room at the ridge, as in some hip roof designs, or other factors can cause this.

   But exhaust has to be matched by intake. I have heard about people who think they are going to save a fortune actually have their cooling cost goo up after installing an attic fan. Slap an attic exhaust fan into a gable end of an attic that lacks proper venting and you can develop some pretty strong negative pressure. Pressure that, lacking other way of being relieved, will draw air through the many small holes in most ceilings. Like around electrical boxes, plumbing stacks and ceiling registers.

   The exhaust fan in the attic can literally suck the conditioned air out from inside the house. A double whammy because not only are you blowing out air you paid to cool but this causes the inside of the house to draw uncondioned air from outside the building envelope. Your literally pumping in hot air.

   No AC unit made can cool the whole county. But your little unit will give it a go. Running continuously while the electric meter spins like a top on crack.

   In my experience the fan motors are good, depending on the situation, for around four or five years of dependable service. After that they are on borrowed time. Also note that while replacement motors are available it is usually cheaper to replace the whole unit. Shell and all instead of just the motor.

   I have replaced a couple of motors on these units and it varies in difficulty from a PITA to being a royal PITA. The labor alone can run many times the cost of the entire unit. Take a hint. When you have the roof reshingled get the exhaust fan replaced. If you can't time it with a reshingle job consider replacing the unit from outside even though this means removing shingles and having a roofer seal and reshingle around the new unit.

   From what I have seen most of these units, when not running, provide approximately the same free area for ventilation as the hole they are blowing through. Just like those silly turbines. DOE, back when the government was actually interested in conservation instead of just making the oil companies happy, did a study of roof ventilation. What worked and what didn't. Their conclusion was that attic exhaust fans were seldom economically justified.

   They cited the intake/exhaust issue I mentioned, their tendency to short circuit ventilation schemes, drawing from too close a source leaving the rest of the attic unventilated, and their power draw as a nagging cost. They recommended a balanced and distributed passive soffet and ridge vent configuration as being the most cost effective. Most times these systems can be cheaply installed during a reshingling job.

   Also they mentioned that the cost of the attic fan and the associated running costs would often provide more benefit if sunk into additional attic insulation, weather stripping and detailed sealing of the building envelope. This, IMHO, makes a lot of sense.

   In theory if you have enough insulation and a tight seal between attic and the living space below it doesn't much matter how high the attic temperature rises. Sealed attics have been touted as ideal in some climates. Not sure I buy all that at face value.

   Some of these folks claim attics don't ever get over 140F. I used to take a thermometer with me into attics and taken temperatures of 155F. Of course at the at temperature the number is meaningless. Bottom line that it is too damned hot. But then again I figure most of these experts haven't been in an unventilated attic, with a corrugated iron roof, in August, at about 3PM on a nice, sunny, windless, day in Florida.

   After twenty minutes of that I sometimes faintly hear the "Colonel Bogey March" and have been known to stumble down the ladder and hear myself mumble something that sounds like: 'None of my officers will do manual labor.' Slightly before collapsing into a heap.

   I don't know why.

1. 
   DerfGreen | Jul 24, 2005 05:19pm | #5

   Hello 4LORN1,

       Thanks for your informative and humorus reply. You confirmed my thoughts that a passive system would work just as well without all the gizmos waiting to be replaced.

                                                                                      Derf Green

2. 
   jrnbj | Jul 31, 2005 05:41am | #6

   True enough re replacing the motors...tho when it's a third storey roof with a pretty good pitch, replacing the moter starts looking easy....
   Re the ridge vent & soffit vent.....well, now that it's become codified (you can't put a roof on without one now, most places), it seems to me it's also become almost useless, because 1) homeowners bitched so much about "seeing" the first bulky ridge vents that manufacturers came up with the current low profile ones, and 2) cooked up some numbers showing how well they work...all in all, while the physics behind ridge & soffit vents is real, as near as I can tell the current implementation is almost useless..."hey, who cares, the inspector passed it & we're hopping from our SUV into our Acond. house .....