What is a duct fan? It is a fan that is placed in the ductwork in your home to move air from one part of the house to another. Why did we add a duct fan inside the ductwork in our home? It is because we have a second floor that includes an office, a bathroom and what we call the craft room. Our air conditioner unit just could not get enough air to the upstairs. During the summertime months, it was always too hot and during the winter months, it was always too cold.
The new HVAC system we had installed in our home last year was supposed to be large enough to heat and cool the entire house. The job turned out that when the house was built, the initial contractor made some glaring mistakes.
We had ducts that did not go anywhere and/or were not sized right for the air flow required. When the new air conditioner was put in, that was all fixed except for the duct going to the second floor.
We weighed our options and decided to put in a duct fan and hither is how I installed it.
I cut open the supply duct before it went into a supply distribution box. The dispersion box supplied our upstairs registers. Our duct was 12 inches, so inserting a 12-inch fan was not a big deal.
I then cut into the flex duct and pulled the Mylar and fiberglass material back.
I checked for the air flow direction pointer on the side of the fan to make sure I did not have the fan facing the wrong direction. Then I inserted it.
The duct fan itself is just a hard galvanized metal tube with the fan mounted in it and two wires hanging out through a plastic grommet. I mounted a standard metal electric box to the side of the fan housing that will allow Maine to connect all wiring in a protected enclosure. I really hate to see wires lose and just connected together. Also, the National Electrical Code requires it.
The next step is to reattach the supply duct to the fan. Once again slide the Mylar liner over the outside of the fan housing and tape it using Foil Sealant tape, mastic tape or butyl tape. All these tapes are a metal faced tape with a soft foam lining to seal the tape to the duct. It is really sticky stuff and it works great! Make sure you seal everything as you do not want any air leaks.
Then cover the entire assembly with more duct insulation to keep all air passing through the ducts and non-leaking out. If any air leaks out, you can have condensation on the outside of the fan housing. This water can drip down and ruin your ceiling. I use foil tape with a fiberglass strengthened lining. I also use a foil tape for waterproofing joints and seams against wet and vapor on foil jacket insulation.
Never use the gray cloth tape as it is not rated for this type of usage.
After the electrical work is completed, the last remaining piece of insulation will be certain around the fan.
As a temporary measure to see if everything worked, I wired the fan motor to an extension cord and plugged it in. Immediately, there was cool air in the office area. Within the hour, the temperature was the same on both floors.
Now, to make it permanent, I installed a 4×4 electrical box. It was equipped with an auto/manual override switch and a variable speed motor control.
An air pressure switch was installed in the riser duct to mechanically turn the fan on or off when the air conditioning unit turns on and off downstairs. The objective is to have fully automatic action with minimum electric usage.
The total cost to install the duct fan and the controls were less than $200.