Install Your Own Whole House Exhaust Fan
Part 2 of 2
A typical attic floor/interior ceiling installation...
Years ago, when a person purchased an attic fan they prayed for divine guidance! The instructions were designed to discourage the home handyman. Today's fans have very precise and thorough instructions. So rather than go into extreme detail, I will give you a short graphical presentation of a typical installation... with comments. Though your own installation may vary, the principles are the same.
Many attic fan kits can be installed without making any carpentry modifications to the ceiling joists... the wood beams that support the ceiling. This makes installation of these fans less demanding of your skills. In fact, in this particular installation, there was no cutting of the framing whatsoever! The key is choosing the right location.
Attach the template to the ceiling...
This particular fan was designed to be installed on ceilings with joists 16" on center. "On center" is the distance from the center of one joist to the center of the next one. If you have a ceiling with 24" centers (common with truss construction), or if you could not center the fan template over a joist as shown due to some obstruction, you would have to do additional framing. This framing forms a "box" for the fan to seal against.
A template, or cutting guide, for the location of the ceiling hole was supplied with the fan. This guarantees an almost mistake-proof layout for your ceiling louvers. In this photo, a twelve inch square of drywall was cut out from the ceiling with a drywall saw. A similar-sized square was cut out of the center of the cardboard template. This exposed the center joist to allow for accurate placement of the template. As you can see, the template was centered over a ceiling joist and then stapled (or tacked) to the ceiling.
Cut out ceiling using template as a guide...
Using the template as a guide, the drywall was cut and the ceiling panel removed. The insulation around the opening has been rolled back out of the way. Once the fan is installed, the insulation can be trimmed so that it presses against the sides of the fan frame.
Install fan using supplied brackets and hardware...
The fan frame is now in position over the hole in the drywall. The fan is normally fastened in place by means of brackets which are screwed to the joists. This particular fan had brackets which also aligned the fan over the center joist, making placement easier.
Seal gaps between joists with supplied spacers or make them yourself!
Once the fan is in place, it is obvious that something is missing! There are openings between the joists that must be filled. The fan kits come with special spacing material to place between the joists to completely seal the fan base. This kit supplied the installer with black plastic panels (see arrows) that can be cut with a knife or snips to fit between the joists. The instructions called for nailing the panels to the wooden fan frame. I recommend the additional step of sealing between the plastic panels and the joists with an adhesive caulk... any type will do. You will get a better air seal and they will definitely stay put when you turn the fan on!
The final results look great!
This is the final view from the upstairs hall. All that is visible are the louvers, which are attached to the ceiling over the hole.
Obviously, the particular situation of YOUR job may require more carpentry or other creative efforts, but it will all be worth it!
About the louvers that come with the fan kits...
There are two styles of louvers that may come with your kit. The one pictured above has a low profile to the ceiling. There are special cut outs in the louvers so when they open, they flip upwards into the attic space and clear the center ceiling joist. This style offers little room for installation error. If the fan is not precisely centered over the middle joist, the louvers will not open but instead hit the joist.
There is another style of louver that has a frame that is a few inches thick (below). The louvers open within the frame, so they are not dependent on any open space above the ceiling and minimize carpentry modifications to the ceiling joists. These allow more flexibility in your fan's positioning. However, you do not have a choice of louver style as an option... the kit you purchase may come with either type of louvers, but not both.
You do have another option, and that is to build a wood frame and raise the recessed louvers yourself. Here is a picture (below) of one such installation. The wood frame that holds the louvers in attached to the original frame of the access trap door (or should I say "former" access trap door). The wood isn't finished/painted yet, but you get the idea. If this was my place, it would be finished... at least within 10 years of installation (or less if I was gently nudged by my better half!)
Drumroll, please. And Natural Handyman's personal preference is...
OK, fine... since you asked my personal preference is the former, thinner set of louvers. For all the added grief in getting the position precise, the appearance is much more professional and dare I say finished looking. But if you just don't want to deal with the carpentry, by all means use the raised louvers. I don't judge.
Prevent heat loss in the winter months by insulating your fan...
The attic fan louvers you installed in the ceiling have virtually no insulating value. Most of them don't even seal very tightly... metal to metal without any weatherstripping. This means that there is substantial heat loss possible unless you insulate them. There are two ways to do this, depending on where your fan is installed:
If your fan is on the attic floor above the louvers... the easiest way is to make a box from plywood that will fit easily over the entire fan assembly. Use at least 5/8" plywood for strength, and both nail and glue all joints. TIP: Install one or two metal handles on the top or sides of the box to make moving it much easier!
The inside of this box can be lined with solid foam insulation available at some hardware stores and all home stores or lumberyards. Simply cut the foam with a utility knife to fit each side of the box and glue it in place with construction adhesive. (Note: be sure you use a construction adhesive that is designed to be used with foam insulation... some adhesives do not adhere well to plastic foams.)
If you want to get really fancy, install a removable or hinged cover on the insulation box, so that you need not remove the entire box during "fan season".
If your fan is gable-mounted... like the fan shown at the beginning of this article, the ceiling louvers are more accessible and can be insulated directly. You could lay batts of insulation directly over the top of the louvers but this may cause fiberglass particles to migrate into your home. Instead, lay a plastic tarp or thin plywood cover over the top of the louvers before laying the insulation.
If you want to be scrupulously neat, you can bag the insulation in large garbage bags and then lay the bags over the louvers... just make sure that the insulation is not packed too tightly into the bags. Compressed insulation loses much of its insulation value.
Important and life-saving tip... be sure your fan is wired safely!
I mentioned this earlier, but it is worth repeating. Your fan wiring must comply with the local electrical code. Most codes require a separate circuit for an attic fan. If you try to wire it into existing circuits, dimming of lights and overload of the circuit are almost guaranteed. This is especially important if you have a refrigerator, 50" rear projection TV, microwave (for popcorn, of course) and other powerful diversions in your bedroom... which happens to share the same circuit!
One important electrical safety device that should be installed on all attic fans is a fusible link. This is a special type of fuse that responds to heat. The conductive element is made from a low melting point alloy that will disconnect the fan from power in the event of fire. The fusible link is installed in the attic between the whole house fan and its power supply..
The most efficient way to use your attic fan...
You're probably saying to yourself, "I can turn the fan on... what's your point?" Having used one for over 15 years, I think I can give you amateurs a few tips! Since the purpose is to change the air in the house, you should open a window in each room you want to ventilate. Opening too many windows too wide will affect the other soothing effect of these fans... the cooling breeze. Though you will still be moving air, the effect will be so diffuse that you may not even know the fan is on... except for the low frequency background rumble!
Just as with your forced air heating or cooling system, you can regulate the rooms that get the most air movement by selectively opening and closing windows to get the most comfortable air flow throughout the house.
Make sure enough windows are open... or else!!
Be careful not to start the fan with too many windows shut. This can cause air to be drawn down chimneys and air ducts, adding undesirable odors and possible contaminants into your home (i.e. carbon monoxide-laced furnace!). Though fireplaces and wood stoves are not generally used in the summer months, many homes use oil to heat their water. Reversing the chimney flow is not desirable or healthy!