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Are Register & Duct Fans a Solution for Uneven Heating & Cooling?

February 15, 2015

Are some rooms in your home too warm or too cold?  Does one floor of your house get much warmer or cooler than the other?  Do you find that some vents blow lots of air while others – usually those farthest from the HVAC source – hardly blow much air at all?  No matter how you set your thermostat, does it seem there is always one (or more) room(s) of your house that don’t seem to get to the desired temperature? What can be done?

Special fans can help move more of the heated or cooled air already present in the ductwork into the desired room.  Fans on or in the ducts pull this conditioned air into the room, keeping it comfortable longer, so your furnace or air conditioner will run less often, lowering your utility bills.  But do they work?

Register Fans
Register fans also called in-floor booster fans are small fans that sit directly in or on the register(s) in the problem room(s).  A few kinds are pictured here.  They are easy to install and inexpensive usually less than $80 each. Some come in different colors, have their own thermostat, are multi-speed, or can be electronically controlled.  Most users of register fans find them noisy and prone to frequent failures/burnout.  They can also be a bit cumbersome since they have an electrical cord that needs to be plugged in (wires dangling across the room).  Most of these small fans are akin to the fan inside the typical desktop computer, and they are not rated with a high enough airflow (cfm cubic feet per minute) to really make a difference.  Some believe register fans further restrict airflow because the vent is now blocked by fans.  However, a few folks have found this simple solution helps.  At least it’s not too expensive to find out.

Mid-Duct Fan
A good alternative is installing a mid-duct fan also called an inline duct fan.  This is a large, heavy-duty cylindrical fan, taking up the entire width of the ductwork, e.g., they “replace” a section of ductwork. They are placed mid-way between the HVAC source and your problem room(s).   Your HVAC ducting must be accessible and exposed to install and work on it.  They require an electrical outlet or they can be hardwired, and require a relay back to the furnace.  So, you’ll need an electrician or HVAC professional for installation.  Inline duct fans are quieter than register booster fans, and cost $30-$150 each, depending on the size (note: you need to know the size and shape of your existing ductwork so you can pick the right-sized unit!), cfm rating, and features, plus a couple hundred dollars for the electrician.

Uneven Heating & Cooling
The solutions described above may fix the symptom of uneven heating and cooling, but it is always best to address the root cause of the problem.  Here are some of the typical things that may contribute to airflow problems:

  • clogged air filters,
  • air vents or dampers which are blocked by furniture or not opened fully,
  • return air registers that are blocked, cracks/leaks in windows and doors,
  • a dirty blower wheel and/or coil,
  • leaks in the ducts themselves due to peeling duct tape or holes made by plumbing or rodents.

If none of the above things is the source of the problem, you might need to address the problem in another fashion.

Often the biggest challenge is the return air – getting the stale air from the second or third floor back down to the furnace to be heated or cooled and redistributed.  In these cases, the best solution is adding returns or installing a thermostatically controlled zone system.

Having your air duct system professionally balanced might solve the problem and will improve comfort and efficiency.  But if your problem is due to poorly insulated rooms, or undersized ductwork, then no amount of balancing will fix the problem.

The bottom line is that the lack of proper airflow drastically reduces the efficiency of your heating and air conditioning system. Poor airflow decreases system performance, raises utility bills, and reduces equipment life.  It is best to find the root cause of the problem and address it.