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fgillis 02-18-2009 08:29 AM

2nd floor air flow/pressure
Hi, here's my story, hope someone can help...
The house is 2 stories, the furnace is fairly new and powerful. The first floor is fine but we’re having trouble heating/cooling the 2nd floor. The previous owner attempted to add ducts to the 2nd floor during his remodel. Unfortunately I think he made some huge errors in designing his 2nd floor system. The duct for the 2nd floor comes out of the furnace as 8 inches, then after a few feet reduces to 6 inches, he probably should have left it at 8 inches all the way up to the attick and then reduced it to 6 up there. The first problem now is that the duct must make at least 2 turns in the wall before it goes up to the attic to then feed the (4) 2nd floor registers. The airflow is practically nonexistent up there. The furnace blows with a lot of force but it’s the main trunk/duct that’s taking most of the airflow since there is less resistance. The main trunk is rectangle and much larger than the second floor 8 inch duct. So the system is flawed because 1. There’s no return air on either floor, 2. The duct isn’t a straight shot up to the attic causing way to much resistance, 3. The 2nd floor registers are on the ceiling and without any return air they’re pretty much useless. So, the first thing I tried was to install one of those cheap home depot Suncourt booster fans in the attic to help with the airflow for the baby’s room (I know, rookie mistake). It was a complete waste of time, it didn’t help at all. After I thought about it it made sense, since there wasn’t much airflow up there to start with there was no way this little low power fan would make a difference. Next, I wanted to make sure there wasn’t a blockage in the duct leading upstairs, so I blocked off the main trunk from the furnace to force all the power from the furnace to blow up the 2nd floor duct work. There was a noticeable increase in airflow. I still can’t rule out 100% that there’s not something in there blocking some of the airflow but I’m pretty confident that it’s the bends/turns in the duct that is causing the resistance. So, my question is, would it be possible for me to try to add a powerful fan, like a Fantech or a TD-Mixvent Series Multi-Purpose Inline 8" Duct Fan right down close to the furnace so that the fan would be pushing the air up to the attic, I think it would help a lot but I don’t want to spend a few hundred dollars for nothing. I do realize that this isn’t a great solution and I know most of the professionals reading this would advise me to redo the whole 2nd floor system and add a return air duct but that’s not financially possible right now. I’m just trying to make it a little more comfortable upstairs. My other question is this, I can either put a 8 inch fan right before the reducer that goes to 6 inches or I can put a 6 inch fan right after the reducer, which do you think would make more sense? Would the 8 inch be to powerful for the 6 inch duct?
Anyways, thanks for taking the time to read this small novel, I would really appreciate any advice you can give me.

Thanks, Frank

Bob Mariani 02-18-2009 10:17 AM

Bold print is too loud.

fgillis 02-18-2009 10:36 AM

Thanks Bob...... Not bold anymore.....
Any advice for the 2nd floor? I know there's no easy fix for my problem but I'm hoping for a temporay solution for now until I can have the proper duct work and return installed.

Bob Mariani 02-18-2009 11:23 AM

partially closing all the dampers to the trucks downstairs will force more air upstairs.

beenthere 02-18-2009 01:36 PM

Unless the upstairs rooms are little 4 x 4 rooms, you got trouble.

You could need 500, 600 or more CFM for the upstairs. Well outside the quiet range for 6 or 8" pipe.

You can get a fan that will move that much air through those pipes, but the sound may be too much to be able to sleep at night.

It should probably be more like a 12" round feed to the upstairs.

fgillis 02-18-2009 02:18 PM

Thanks Beenthere....

When I do decide to revamp the whole upstairs system would it make sense to run both the supply and return air from the outside so I wouldn't have to rip apart all my walls on both floors? I'm assuming it would be less expensive. If it's insulated enough would it be cost effective?

Appreciate your time and advice, Frank

beenthere 02-18-2009 02:27 PM

Any duct work ran on the outside of the house, adds load to the system.
And by the time the air gets to the second floor, it is either cooler, or warmer(depending on season) then when it entered the duct.

Its best to have duct work kept inside the house.

If you can find a closet of 2, that you can give up some room.
That would be best.

Sparky 55 02-24-2009 04:58 AM

Hello, Several years ago, I replaced a boiler system in my 2 story old home. I installed a 90 Plus furnace in the basement (without) central air. I ran 4- 7" ducts up through closets to the 2nd floor for heat only. Along with the duct system in the basement, this provided all the heat I needed for both floors. I then installed a basic air handler in the attic with the 3 ton AC system, installed vents in all the upstairs ceilings, ran a few downstairs through closets to the first floor rooms. This design heats and cools my house evenly (heat rises, cold falls). Ductwork and air handler in the attic is not that expensive. Moving the AC to the attic unit could cost if your existing system system cannot be retrofit. I've been in many 2 story new homes and hardly ever see the AC work right. That's why I installed this way.

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