I have a home that was built in the early 80's with all original fans. They are exceptionally loud and don't move much air. I would later find out that my fans were packed solid with insulation which explains much of the problems.
Our house also has only one window per room which limits the airflow when the windows are open.We can open them in the summer but due to the layout and placement, it doesn't do much. Usually, we put fans in the windows but that limits the ability to see through them.
This project is aimed at solving two problems. The first is the lack of airflow in the bathrooms, the second is lack of airflow through the windows. By installing multiple, high capacity and high efficiency bathroom fans we can vent bathroom humidity and create enough low pressure that cool night air will be sucked in open windows.
It's the same concept as an attic fan, I've just moved the attic fan to the bathrooms.
You will need:
The largest cubic feet per minute and quietest fan on the market. At the time of writing this, that would be the Panasonic FV-40VQ which this instructable details. It moves 380 CFM and is only rated at 3 sones and runs on 111 watts (the fan I replaced was 50 CFM, labelled 2 sones, and was way louder). I also bought a smaller fan for our master bathroom which is just a few feet from my bed. In total, I have 570 CFM of exhaust fans which is roughly like sticking a box fan on its lowest setting in an open window.
Step 1: Remove Your Old Fan and Cut Your Hole
TURN OFF YOUR POWER!
Start by taking your old fan out. Sometimes, they are screwed in from tabs that you can reach without cutting your ceiling apart, but don't plan on it.
Remove the motor. There's usually a screw holding the motor assembly in place. Once that is removed, the whole thing just drops out (mine hit me in the head, try not to do that). Then, disconnect the power from the old fan.
Mark the square that you need to cut (if you need to cut). Make it a little smaller than you actually need. It's better to need to cut more later than to have cut too much now. With your larger hole now open, finish removing the old fan housing.
Step 2: Prepare the New Mount If Needed
I thought my rafters were 16" apart and was not anticipating having to do this. I figured the fan would slide right up between the rafters and I could screw directly into them.
That said, I needed to reinforce the mounting for this fan because it is so much larger. I cut a 2x6 (you can use a 2x4, I just didn't have enough laying around) to 22.5" and then made a 16x8" box. Those were then screwed into place.
Move any electrical wires out of the way.
Step 3: Remove the Inner Housing, Exhaust Vent, and Electrical Box; Install the Fan
I didn't get many photos of this step. Remove the inner shield. Take the exhaust vent and electrical box off the fan BEFORE getting on the ladder. Then, wire your fan's electrical box with power. Put that box and the vent in the ceiling on the side where the fan will vent. Don't push it too far back, you will need it shortly.
Install the fan using the supplied screws.
With the fan installed, reach up into the exhaust port and grab the vent that is laying in the ceiling. push your hand through the flapper so that you are holding the whole thing but the actual vent. Finagle the vent back into place and replace the screws. I found it easier to put the screw in the electrical box before the exhaust vent.
Replace the inner shield.
The cover for this fan is really flimsy and cheap but it installs easily. just bend the wires together and slide them into the openings.
Turn the power back on and check your work.
Step 4: Vent Your Fans Properly
I have a few other attic projects going on this year so I didn't finish venting this to the outside. Technically, it's ok to vent the fan to the attic (at least to my knowledge) but you should still use a piece of duct to aim the vent up into the open space, not blow moist air on your insulation. Venting straight into your attic increases the risk for mold growth. However, as long as you have proper ventilation, there should not be an issue (I still don't recommend it).
Ideally, you will vent your bathroom fans to the outside. I'll cover that a little later in the year
Step 5: Final Thoughts
Make certain you cut your hole correctly. Mine is just a hair too large.
The fan creates enough of a low pressure area to draw air in through a window in our bedrooms. It isn't a huge amount of air, but with both fans on, we should be able to cycled the air in my second story every 12-15 minutes. That's enough to help cool the second story during the cool evenings of summer.
Checking the math, my two fans will run on 150 watts/hour. An AC unit is somewhere between 3000 and 5000 watts/hr. The potential savings is high for a couple months out of the year (this isn't a solution when night temperatures are in the upper 80's).
Also, eBay routinely has fans on sale. I had to wait a while for these specific fans to appear at decent prices but I was able to get both for under $200 total.