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docholaday 06-02-2007 11:13 PM

in duct boost fan
I recently purchased an older two story condo and the air flow to the second floor is very weak. There also aren't any returns on the second floor. I was thinking that a quick and easy fix would be to add a boost fan in the crawl space just before the 12"x8" duct went upstairs. The only problem is that I haven't had any luck finding a 12"x8" fan. Any help on an alternative solution or info on where I can find one would be much appreciated. Thanks!

pjpjpjpj 06-06-2007 12:58 AM

I'm no expert or contractor but the only inline fans I have seen available are for mounting in round duct - in only 6", and possibly 8" round sizes. Most likely, those wouldn't provide enough airflow even if you could cobble together some funky transition fittings.

Does the 12x8 go up to an attic and then feed ceiling grilles in various rooms? If so, you might be able to add round booster fans in the individual runouts to the grilles, which would be like "pulling the air up from above" rather than "pushing it up from below".

I installed a 6" round inline fan in my basement, for a runout to a grille in my second-floor bedroom. It makes a noticeable difference, although it is louder than I would have liked (the whirring noise follows the air right up the duct into my bedroom).

Of course, the easiest solution, if your first floor is always comfy, is to shut grilles on the first floor to force the air upstairs. If you don't have dampers in the grilles (okay, technically if it has a damper it is called a "register"), you can buy magnetic sheets that stick on the face of the grille and block airflow... or use tape and cardboard.... :)

Otherwise, with no second floor returns, you are sorta stuck, due to the design. If you had returns in the rooms, you could close the doors, which would help keep the cold air (which sinks) from falling down the stairs to the first floor. But since you have no upstairs return grilles, closing the doors would just stop airflow and further inhibit supply air from getting to the upstairs rooms.

docholaday 06-07-2007 08:42 AM

The 12x8 runs up to the second floor and runs thru a bathroom followed by a bedroom and then another bedroom. The last register in the line provides little or no airflow.

I have basically closed all of the registers on the first floor to force the air upstairs, which works ok, but I would like to increase the aiflow upstairs if possible.

Thanks for your help.

mab20009 06-13-2007 03:03 PM


Originally Posted by docholaday (Post 48133)
I have basically closed all of the registers on the first floor to force the air upstairs, which works ok, but I would like to increase the aiflow upstairs if possible.

I have a similar problem where the second floor of my condo does not get adequate airflow. I tried closing registers, but I must have closed too many, as a couple of days after doing so, my evaporator coils froze solid. Symptoms of this are usually low refrigerant or poor airflow. I re-opend the registers on the first floor and let the fan run on the coils to thaw them out. Once thawed, I re-started the A/C, and the coils did not freeze up.

So, just a small warning. Closing too many registers might inhibit your airflow enough to cause a freeze up.

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