Do duct booster fans really work?


Old 09-09-13, 09:49 PM
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Do duct booster fans really work?

I am having trouble cooling one particular bedroom on the 2nd floor of my new home. It's a brand new A/C system, installed in a 1960's era home. It already had forced hot air heating, so A/C was added to the existing system. I did a lot of research already, and I realize the ducts were originally sized for heating only.
Anyway, the main ducting is exposed in the basement. and there are 4 "feeders" that supply heat/cooling to the first and second floor. Starting from the rear (Back) of the house, and working towards the front. The first feeder supplies only the kitchen (it is clearly visible). The second feeder, supplies the two smaller bedrooms (I believe). The third feeder supplies the bathroom, and the last feeder (at the front of the house) supplies both the first floor living room, and the second floor master bedroom. The duct seems to split the air between the living room and master bedroom. I took off every register, cleaned them out the best I could with a vacuum cleaner. And discovered that inside each duct, it has a movable metal piece, so as to balance the airflow, as they say. Plus each register has a knob on the outside to adjust it also. I was able to make it cooler in the second bedroom, just by closing some of the internal louvers on the 1'st floor (the ones inside the duct, not the lever on the register itself). But I still find the middle bedroom uncomfortable and hot. The thermostat is on the first floor in between the living and dining room. There is a huge return vent in the dining room, otherwise, only a supply vent in the living room and kitchen. On the second floor there is a return duct in every room except the bathroom and hallway. Since the feeders are all located inside the walls on the first floor, I can't get access to them. I wonder if adding a duct booster to the second feeder in the basement would help?
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Old 09-09-13, 11:49 PM
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Although there is the rare instance generally duct booster fans do NOT work. If I understand what you have, I can almost assure you that a booster fan will not work.

Unfortunately, the only real solution is to install larger ducts. Or a second A/C unit for the upstairs.
Old 09-10-13, 04:34 AM
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I have to dis-agree. I recently had A/C installed on on 1970's built home. I was told by contractor not to expect the second floor to get very cool. I looked into vent fans but cost was not worth it. Instead I just bought several small fan and put them over the vents pointing up. They work so well I'll keep them running during the heating season also. I just plug them in and leave them running almost 24/7.
Old 09-10-13, 05:03 AM
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Duct fans are a very short term solution.
Even if they do help with a particular room they would have to operate 24/7 and being a sleeve bearing motor will not last long.

One thing you could try is to increase the speed of the blower fan to increase volume/velocity and re-balance the ducts.
If a belted blower you would increase the size of the motor pulley and test motor to ensure it is not overloaded, if a direct drive make sure it is connected to the highest speed tap.

Maybe even a blower change is possible so if you check this out and give us some info we may be able to offer more.
Old 09-10-13, 05:12 AM
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Duct fans made for this purpose are usually thermostatically actuated. So they won't run 24/7. Only when the A/C is on do they operate. However, your correct that keeping a cheap small desk fan running 24/7 will wear out the bearings. But consider cost. They are cheap and should last several years.
Old 09-10-13, 05:43 AM
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There's dampers, so the first thing I'd do is adjust them further to force a little more air upstairs.
Are the vents at floor level? If so, consider a ceiling fan to keep the air circulating.
Old 09-10-13, 06:43 AM
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You're very fortunate that the thermostat is located in a room farthest from the furnace (on the first floor at least). The AC will run until the thermostat is satisfied so you should be able to greatly reduce flow to the closest (and coldest) feeders and allow more cool air to reach the far feeders & thermostat. No guarantee the re-balance will make that last room comfortable, but it should help.

I have the same problem but my dampers are covered by a finished ceiling in the basement.
I've considered a booster as well but my "band-aid" was to install a window AC in the hot room--which is the master BR on the 2nd floor.

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