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Whole House Exhaust Fan Q&A

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Dear NH,

I have a belt-driven whole house exhaust and that is mounted above the ceiling in our hallway. I want to install some sort of insulation to keep the cold air from coming into the house. I can't install the type of kit that covers the fan from above because I would have to walk about 80 feet through 3' of insulation! Currently, I use plastic storm window "stretch wrap", but it doesn't provide much insulating value. The fan is made of a non-metallic substance so magnets will not adhere. Does anyone make a kit that attaches to the surface of the louvers?

SP

SP,

I am unaware of any prefabricated kit you could purchase for this application. Using the plastic storm window was a creative solution and probably helps more than you think; of course, adding some sort of insulation would give you even more energy savings.

Though it would take a little effort twice a year, you could take down the louvers seasonally and replace them with a smooth plywood board (1/4"). This board can be painted or stained, and can even be "dressed up" with moldings, depending on your desire, abilities and creativity.

Match the locations of the mounting holes to the louvers and if you want, use the same screws to install it. Once you have access to the area above the louvers, you can decide which type of insulation will be the best for your situation. A solid board insulation such as Styrofoam, cut to fit as precisely as possible, will give the most insulating value per inch of thickness and also be neat (especially as opposed to fiberglass). You could also put some fiberglass into a plastic bag or two and push that into the opening to provide insulation. Yes... I know that gravity is your enemy, so you will have to be creative in finding a way to make the insulation stay in place. Whether you can attach it to the wood cover will depend on the framing beneath the fan.

Some attic fan installations leave the ceiling joists in place. If so, your opening will probably have a ceiling joist crossing it, which will allow you to press bagged insulation into the gaps on either side of the interloping joist. This will provide an adequate air seal and provide neat, reusable and efficient insulation!

Of course, even if you didn't use any insulation at all, just having a solid cover as opposed to the louvers (or the plastic film) will make a dramatic difference itself.

To make take-down and installation easier, you can replace the original screws with double-threaded screws. These screws have wood-screw threads on one end and machine-screw threads on the other. Once installed, you leave the screws in place and just remove washers/nuts to change covers. To initially tighten this type of screw, put a nut onto the machine screw end all the way on and use a wrench to turn the screw. The nut may be a little difficult to remove, but you can hold the machine threads with a pliers to keep the screw from turning while removing the nut. It is better to grab the machine threads near the middle, not at the end. You might damage the threads enough to make it difficult to start the nut next time! Any slight distortion in the "middle" threads, though, will be adequately straightened when you remove the nut.


Dear NH,

Is a quiet whole house exhaust fan an oxymoron? I am looking for the most quiet whole house fan I can find. Can you please recommend one?

EH from Vernon, NJ

Dear EH,

Sorry, but unfortunately I don't have that information. Whole house exhaust fans are all somewhat noisy and are not rated for noise levels like bathroom exhaust fans and many other appliances. Comparisons are impossible without data!

About the only advice I can give you is... if you are willing to do (or pay for) the extra installation carpentry involved... to purchase an exhaust fan that mounts on an outside wall instead of the floor. This will eliminate much of the vibration and noise that is typical of the attic floor mounted fans.

If you haven't done so as yet, read our article on whole house exhaust fans or see our links to whole house fan companies.


Dear NH,

I am very interested in installing some sort of whole house ventilation, particularly a floor mounted attic fan but have run into a possible snag. Some people that I have talked to say there is a requirement for minimum headroom above the fan in order to prevent backwash and slowing the fan down. I read your article about installing these fans, but saw nothing about this problem. Our attic, in the any area that would afford a good location for a fan, is only about 30" high. There is no setting where a gable mounted fan would be suitable. Our house is 2 stories, about 2800 SF with 8' ceilings throughout. Can you give any advice?

CB

Dear CB,

I have heard of this problem, but the fan will still work... just with less efficiency. There is a reasonable carpentry fix for this problem. You can install plywood (1/4" is plenty thick) across the roof rafters directly above the fan and extending at least a rafter space (16"or more) beyond it on either wide. The flat surface of the plywood will allow the air to move more smoothly instead of getting trapped in the spaces between the rafters and causing the backwash. Don't put any insulation behind the plywood and leave a slight gap where the plywood meets at the peak. This will allow for air circulation behind the plywood.

This is not a perfect solution but it beats raising the roof! Assuming you have enough venting at the gable ends, you should get a reasonable amount of venting... just don't buy too large a fan for the available venting.

As an afterthought, you could go whole hog and install a cupola above the fan! By opening up the roof beneath the cupola (many modern cupolas are decorative and rest on top of the shingles rather than providing attic ventilation) normal attic ventilation will be improved and your exhaust fan will get a breath of fresh air, too! One good resource with plenty of links to online manufacturers is CUPOLA at http://www.cupola.com .


Dear NH,

I have a problem with a whole house fan installation. I can't install a 24" fan in my 36" wide hallway! Because of the design of my home, this hallway is the only location I can locate the fan. My attic uses trusses on 24" centers, but the location of the trusses prevent the louvers from opening, no matter how I try to locate them. I have been told DO NOT CUT THE TRUSS, so I am in need of some advise!

SK from Geneva, IL

SK,

Yes... under no circumstances should a roof or floor truss be cut without consulting an engineer. Trusses are rather flimsy, but they get their strength through their design. Any cuts can make a truss dangerously weak and possibly make your roof unstable!

There are a few ways to skin this cat without tampering with the trusses. You could, for example, make the truss irrelevant (at least the part in the attic) by installing a through-the-roof powered turbine fan instead. Of course, I understand that this may not be possible if you dislike climbing on the roof or if your home has restrictive zoning rules or property covenants.

You may be able to use the floor/ceiling fan anyway if you have the clearance to mount it. Though the ideal situation is to have the fan located directly above the louvers, this is not an absolute requirement. It is also not an absolute requirement to have a totally open space between the fan and louvers. A few boards in the way are not a "deal breaker". Just improvise! If the members of the truss force you to offset the fan even as much as a foot, you can still creatively box in the fan so that there is a closed shaft... however crooked... between the louvers and the fan. Of course, the more obstructions there are, the less efficient the fan will be. But having a fan work at 80% is better than 0%... at least the last time I looked!

No... I have not been avoiding the question of the obstructed louvers. As I mentioned in the article at http://www.naturalhandyman.com/iip/infattfan/infattfan1.html , some attic fan manufacturers supply a flush-mounted louver assembly that mounts right on the ceiling, requiring no clearance above. I do not know of any manufacturer of this type of louver that sells it independently of the fan. But if you can perform a little simple carpentry, you can solve the problem. Build a wood frame from 1" nominal pine boards for the louvers to provide the additional clearance you need. Mount the frame on the ceiling first... then mount the louvers to the frame. Once primed and painted to match the ceiling, the frame should be unobtrusive and functional! Use a quality adhesive caulk to smooth any unsightly cracks between the frame and the ceiling prior to painting.

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