Low air flow on 2nd floor - http://www.hvacmechanic.com/ Forums
Original message
| bobandgeri
 |  "Low air flow on 2nd floor"
, posted Wed 16 Jul 12:39  
1st let me start by saying I have called two of the recommended local professionals - one canceled and one only tried to sell be on a yearly service contract and a new furnace - the furnace and house are only 8 years old. Filter is changed every 6 months - has a air bear 5 inch thick filter and was just changed - very little dust in the blower compartment.
We have a Goodman Model GMPN100-4 with 2 zones run by a Trol-a-temp zone controller. The house has a hip roof with soffit vents all around and has full southern exposure.
During the hotter days we noticed that the 2nd floor wasn't cooling down very fast. The first floor is fine. The temp of the cool air at one of the vents (1st floor measured) is 55 degrees.
It appears as though the air flow on the 2nd floor is about half of the first floor at any given vent. The 2nd floor has 8 vents while the 1st floor has 7. We also noticed that when the just 2nd floor is running there is still air coming out of the 1st floor vents, although much less than when the 1st floor is calling for AC.
This leads us to conclude that either the 1st floor damper is not fully closing or the 2nd floor damper is not fully opening and the 1st floor is opening to dump air pressure as designed.
Since we are probably not going to buy a new furnace we bought a 10,000 btu window unit for our master bedroom as an auxiliary to get us through the hotter days (basically to cool the bedroom down at night for sleeping) as it was only $208 with a high energy rating. But do want to see if we can resolve the issue.
Questions:
Are we on the right track?
I have easy access to where the dampers are located on the 2 main feeds - anything I should be aware of before I try pulling it out to test if the dampers are fully opening/closing?
Would a Power Vent installed in the attic roof help?
Any other suggestions?
Thanks in advance for any help.
I don't know what I don't know
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Replies:
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| Freon
| "Re(1):Low air flow on 2nd floor" , posted Wed 16 Jul 14:47
See if the dampers can be manually set. If so set the 2nd floor fully open and 1st floor fully closed.
Now the most important question. How many ducts go from the 2nd floor damper supply to the 2nd floor and how big are they? I have a feeling you may not have sufficient supply ducting. 8 vents (assuming 6" supply duct to each vent) would need close to 900 cfm of air flow which is ~12" or 14" diameter duct.
Where are the return registers for the 2nd floor located? How big is the 2nd floor return ducting? Is the 2nd floor open to the first floor through a stair well? If so much of the 2nd floor cold air will sink to the first floor. That's why 2nd floor returns are important.
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| | bobandgeri
| "Re(2):Low air flow on 2nd floor" , posted Wed 16 Jul 17:51
> See if the dampers can be manually set. If so set the 2nd >floor fully open and 1st floor fully closed.
No - the dampers cannot be manually set - only electronically
>Now the most important question. How many ducts go from the 2nd >floor damper supply to the 2nd floor and how big are they?
There are 8 ducts that go from the 2nd floor supply to the 2nd floor. They are 7 inches in diameter. Both supplies are the same size - 20x8 while the single return for both zones is 24x8
>Where are the return registers for the 2nd floor located?
The 1st floor is open to the second via an 8 foot wide staircase and hallway - the stair case is in the living room which is 2 stories high.
Off the hallway are 5 doors, two on each side one at the end (closet) 1st room on left is a guest bedroom - it has supply and 1 return. 2nd on left is the guest bathroom - 1 supply only. 1st door on right is a bedroom used as an office - 1 supply only. 2nd door on right is Master bedroom 2 supplies and 1 larger return. Off the Master bedroom is walk through bathroom with 1 supply. Through the bathroom is a large walk in closet over the garage - 2 supplies.
>How big is the 2nd floor return ducting?
All ducting appears to be the same size - 7 inches
>Is the 2nd floor open to the first floor through a stair well?
Yes
>If so much of the 2nd floor cold air will sink to the first floor. That's why 2nd floor returns are important.
3 of the 5 doors on the second floor are kept shut - we've tested shutting them all with no differance. We've also tried shutting the vents in all room but the two in the bedroom and while we did see more air flow it still wasn't as much as the vents on the first floor get.
I don't know what I don't know
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| | Freon
| "Re(3):Low air flow on 2nd floor" , posted Wed 16 Jul 19:08
Having 8 separate 7" ducts may be part of the problem. Put your hand up to a 2nd floor supply register. Feel the strength of the flow from the register (air velocity). Now drive your car 5 mph and hold your hand out the window... same feeling as the 2nd floor register?
Do you find the cooling in the roome with their own return registers is better?
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| | bobandgeri
| "Re(4):Low air flow on 2nd floor" , posted Wed 16 Jul 19:42
Can't do the test drive at the moment - but the air flow out of the 1st floor is much greater than the second floor.
The rooms with their own return really are no differant than the ones with. In fact the only room we really care about upstairs is the master bedroom and bath - the bedroom has it's own return.
I am mostly puzzled as to why the registers on the first flow have air flow (all of them) even though the first floor is not calling for AC. I have the second floor set at 75 and the first flow set at 78 and I feel a definate air flow out of all 7 registers on the first floor.
I don't know what I don't know
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