Description
Power Vents Remove Dirty Air
A power vent can remove dirty air from a room to outside. In many cases you can install a power vent without adding make-up air. If the building you are in has gaps in the walls and places where air can seep in from outside or other adjacent areas the power vent works well enough. If the building tightly sealed you will need to find a way replace the air you are exhausting. This can be done using a make-up air unit like the LAC-MUA-900.
Three Duct Adapter Sizes
The LakeAir LAC-MUA-900 is available with 3 different duct adapter sizes. These sizes are 12, 10 and 8 inch. The larger the duct size the more air you can efficiently move with your make-up air unit.
The reason air flow drops in duct work is friction. The smaller the duct the larger the amount of friction and the smaller air flow. The type of ductwork makes a difference as well. today the most popular ductwork seems to be flexible round ducting. In comparing the 3 duct adapter sizes available lets look at a 20 foot run of round flexible duct work. The table belows illustrates how the diameter of your air duct and the duct type influence your loss of air flow due to friction.
| Duct Type | Duct Diameter | Duct Length | % of Air Flow Loss to Friction |
| Flexible Round | 12 inch | 20 feet | 0.18% |
| Flexible Round | 10inch | 20 feet | 4% |
| Flexible Round | 8 inch | 20 feet | 13% |
| Sheet metal | 12 inch | 20 feet | .01% |
| Sheet metal | 10 inch | 20 feet | 2.5% |
| Sheet metal | 8 inch | 20 feet | 7% |
Bigger is better and Smooth Surfaces Make a Difference
The table above clearly demonstrates that using a larger duct size is to your advantage. There is almost no loss of air flow in a 12″ inch duct. If you are running a very short length of duct the size is not as important. The longer the run the more friction the air will experience. For instance is our first row where the duct was 12 inch flexible, at 20 feet there was a .018% loss in air flow, when the duct length was increased to 50 feet the percentage of loss went up to 0.44% To get more information you may want to consult an HVAC technician. We will try to help
The friction losses in the top 3 rows are when flexible duct work is used. Because of the way it is constructed the friction is nearly doubled compared to smooth sheet metal ducting. While metal ducting is more costly, it is also twice as efficient. We urge you to take all of these matters into account as you plan your clean air project.
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