Replies

1. 
   Clewless1 | Mar 08, 2009 05:56pm | #1

   I think the big box stores typically have a thermostatically controlled attic fan (about 14" diam). I've used them to vent e.g. a sunspace. Then you get a gravity backdraft damper (order maybe on line or your local sheet metal/HVAC guy) ... which is aprox 14" x 18" w/ multiple blades. You generally would want to protect it from direct rain w/ some kind of shroud or fixted louvres on the exterior. While it will shed rain, it's not really designed to be weather tight. The stat is teathered to the fan by a short length of flex conduit. The stat setpoint is adjustable.

   The fan tends to be a little loud ... so what I did, was frame a box around the fan after I install it on the wall. Fill that with insulation and then drywall/finish it. That absorbs a fair amount of sound. You could build a similar box entirely around it w/ e.g. one side open, line the back side w/ e.g. acoustical tile, insulation surrounding the fan enclosure. This would eliminate the direct sound path from the fan itself ... further minimizing noise ... and it hides the fan from view.

   The fan might run e.g. $40-60 and the damper that much more. Plus the exterior shroud/louvre.

   I've mounted the damper on the inside face of the framed opening, then mounted the fan on rubber grommets on the inside of that. Put the exterior louvre (should have a bug screen built into it) on the exterior of the framing (trim it out to your taste). Frame around the inside as you see fit.

1. 
   semipro | Mar 09, 2009 04:26am | #5

   I considered one of these fans but suspect they'd be way too loud. I like the idea of the insulated duct.

1. 
   Clewless1 | Mar 09, 2009 06:04am | #6

   Generally as far as noise goes ... you pay your money, take your choice. You move a lot of air w/ a physically small fan and you will have noise ... product of the work produced (i.e. volume of air moved) and the size of the fan. A very large diameter fan will move a lot of air w/ less noise ... but it is a large fan.

   Different fan blades will alter the noise aspect and better fan mounting will also reduce noise. A centrifugal fan may produce less noise, but the fan may be more costly and take more logistics to install.

   If noise is a major issue ... you could take my suggestion a step (or two) further ... don't just take air in the side, but make it take another turn (or two). The more you remove the fan from the space, the quieter.

   Remember ... you suggested a simple sidewall mount ... that in itself is a noisy application (at least on the surface). Ducted exhaust w/ a remote fan is the best choice to control noise.

   I recently purchased two Panasonic in-line fans ... various sizes available; I used 250 cfm. You duct to/from them. Mount in any position. VERY quiet fans!!! I used them for bath exhaust ... multiple rooms on one fan. They are so quiet that I often can't tell they are on at all. Panasonic has a quiet reputation in this industry. Maybe they have something for you. You may have to alter your true sidewall exhaust approach a little. You may also have architectural (i.e. aesthetic) issues (although a sidewall mount suggests you either don't or don't really care about that aspect).

   Now ... that's my 4 cents

   Another thought - if you take the frame it in, insulate it and sheetrock approach, you can add sound quality w/ simply adding sheetrock ... lots of mass will help a little. That is one of the ways the code requires STC rated construction ... w/ multiple layers of sheetrock. You could use 4 layers to help a little. Just trying to think outside the box a little ... even if it is 'lame' ... sometimes that will trigger another idea.

   I think I'm up to 5 cents  ;)

   Edited 3/8/2009 11:11 pm ET by Clewless1

1. 
   semipro | Mar 12, 2009 03:16am | #7

   Thanks for the info.  I'm considering doing something similar; a rainproof louver on the outside with a fan mounted behind it in an insulated box duct.  The duct should also allow me to easy close the opening off for winter.  In summer I may put a filter there to keep the fan and louver clean.  Sounds crazy I know filtering exiting air but my experience thus far with fans tells me things will get dusty quick.  The filter may help muffle the noise some also.   I realize it will cut down flow somewhat but that may be worth it. 

2. 
   jimjimjim | Mar 08, 2009 10:10pm | #2

   How much air to you intend to move?

   Would the fan run slowly and continuously, or would you switch it on briefly to exchange an entire houseful of air?

   How much wall space in the cupola can you consume with the fan opening(WxH)?  Can the fan mechanism intrude into the cupola interior or must it fit into the wall?  Do you intend to re-frame to accomodate the installation, if necessary?

   Are there opening windows up there?

   Jim x 3

    

    

1. 
   semipro | Mar 09, 2009 04:25am | #4

   We had a heavy duty box fan mounted in one of the 4 awning windows there that provided pretty good ventilation. It was loud but we ran it at night only for cooling with good results. Windows were left open in bedrooms. Two non-opening small round windows are on the gable walls.I'd prefer to use as little interior space in the cupola as possible but that may be unavoidable. I'm prepared to remove one of the round windows and to re-frame to provide a larger opening for the fan. The round windows are single glazed and condensation there is causing problems anyway. Thanks.

3. 
   GaryGary | Mar 09, 2009 01:26am | #3

   Hi,
   You might look at the fans they sell for greenhouse ventilation -- some of them have automatic shutters, and they are made for wall mounting.

   Gary

4. 
   Jeff_Clarke | Mar 12, 2009 07:40am | #8

   You should mount a smoke detector up there connected to a fan shutdown relay ($20) so that upon detection of smoke in the airstream the fan shuts down (avoiding a quick burn-down if it's still running).

   Jeff

1. 
   semipro | Mar 12, 2009 03:26pm | #9

   That's a great idea that I probably would never have thought of. The chimney affect with the fan being at the high point in the house would be a major hazard. I use X-10 (http://www.x10ideas.com/) to control devices like this in our house so I could interface a smoke detector with that system. Thanks.

1. 
   Jeff_Clarke | Mar 12, 2009 03:35pm | #10

   No problem - I've done this before.   I think you do need to run NM-B4 (4 wire) cable for signalling purposes to interface with the relay.

    

   Jeff

   Edited 3/15/2009 4:30 pm ET by Jeff_Clarke

1. 
   semipro | Mar 15, 2009 04:46pm | #11

   Well, I went and bought a GAC MasterFlow gable fan to try it out but I'm skeptical.  I think it may have too little flow and to much noise.  I've been pondering and remembered I have 2 used HVAC air handler blowers in the garage.  These things pump a lot of air...quietly.  Now I'm considering mounting one of those in a box on the inside wall of the cupola, blowing out an automatic-opening louver (big box had the louver in stock).  Instead of a box with an open end I'd have one with both sides open and the inside end closed.  The only issue I know of now is running a 220v circuit up there, rewiring the existing motor for 120v, or replacing the motor with a 120v model.   Anyone see how this might be a bad idea? 

    

   Edited 3/15/2009 9:47 am ET by semipro

1. 
   brownbagg | Mar 15, 2009 06:11pm | #12

   I always wonder if these whole house fans would suck all the insulation out of the attic