Well I think it has been all of 3 weeks since I last spoke of dryer vent booster fans, but another booster fan had began to cause problems for this homeowner so it appears service was in order. I have talked little about these booster fans simply because most homes do not possess them. Technically by code, they are not allowed, but in some situation such as this multiplex unit, the building inspector must have felt (don’t feel, do the math) the distance to the outside for the dusting was more than enough to warrant a bit of a boost.
Well a little bit about dryer ducting first. When we talk about duct length we are often referring to equivalency calculations because anytime we bend airflow, we need to take that extra resistance into account. A straight 5 foot length of duct is 5 feet, but so is one 90 degree bend. To the dryer, they both look the same. So each time we bend air, use a poorly constructed transition hose, or one of those crappy (yup I said it) louvered vent covers, we need to take that extra resistance into account.
Now in this home, the distance calculated using actual match showed the ducting to be just under 35 feed of equivalency which is under the code requirements for the state I reside in. But I guess each unit has been provided with a dryer booster fan in order to make things better. The bad part was like most people that reside in a home with one of these, they don’t know the booster fan requires periodic maintenance in order to continue to work quietly.
The upstairs neighbor had complained about the noise from this unit as it was right under their feet. The solution was to correct the installation and clean the booster fan so it would not vibrate the floor/ceiling. Sometimes reading and following the instructions is a good thing.