Second floor A/C balancing

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Old 08-11-20, 05:44 AM
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Second floor A/C balancing

I have a home built in 2002 with separate A/Cs for first and second floor. The second floor has Master bedroom and bath + 2 closets and a second bedroom, bathroom and closet on one side of the house and 2 bedrooms and jack and jill bathroom on the other side of the house. WE primarily live on the side with the master bedroom.
The problem is that when we have guests staying in the 2 bedrooms on the other side of the house, they complain that it is too warm (in the summer).
2nd floor thermostat is in the master bedroom
There are 3 supply vents in the master bedroom, 2 in the master bathroom, one in the toilet area and one in each closet.
The second bedroom on that side has a supply vent in the bedroom, closet and bathroom.
On the other side, there are supply vents in each bedroom and 2 smaller supply vents in the jack and jill bathroom.
The air velocity in the supply vents is between 300-400fpm. I don't know what normal should be.

What options might I have for improving the comfort on the guest bedroom side of the house. I believe the AC is working reasonably well but would be open to doing additional checks. The filter was replace around Christmas time.
 
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  #2  
Old 08-11-20, 07:01 AM
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Check the ducts supplying the other bedrooms: Open any dampers there and correct any restrictions (If the branches are flex, it should be stretched tight with no excess length or restriction). Then throttle the dampers supplying the MBR suite about a third. Measure all velocities before and after. You should be able to document increased velocity/flow at the other bedrooms.

Dampers are required at the branch duct connection to the main, look for them (they may be covered with duct insulation) and adjust there, not at the ceiling registers.

300-400 FPM is low (750 is the max. for noise), but there may be more outlets than needed for your equipment, or the "one size fits all" philosophy may have been applied (wherein only one size register is used throughout).
 
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Old 08-11-20, 07:34 AM
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I'd be Interested as to How the FPM was Obtained and Not CFM ?
 
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Old 08-11-20, 08:11 AM
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Quicker Reply ~ is there a Way to Tap into Return Line - Place Small Return in that End Home ..

I have 3 Returns , 1 for Down & 1 for Upper Level & 1 for Basement ~ Basement is only 12 x 12 . .

First Level Return will pull 540~600 Plus CFM in A/C Mode which has been slowed down .
( Too Increase Humidity Control )
Second Level 400~ 490 CFM
Basement Only 150~165 Cfm

Also : Simple Things - Hows the Space under the Doors of those Rooms ?
 
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Old 08-11-20, 08:42 AM
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I am not an expert by any means, but I used an anemometer that give fpm. I probably should have multiplied by the open area to get a cfm.
 
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Old 08-11-20, 08:57 AM
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I really appreciate everyones comments. Interested in learning what is involved.
Each room on that side of the house has a separate return and there is one in the hall way just outside the 2 bedrooms. I probably should create a diagram to indicate the rooms and where the supplies and returns are located.
I need to check for dampers in the lines in the attic.
The gap under the doors for the 2 guest bedrooms is about 0.5-0.75in

Talking with my neighbours (homes by the same builder and same age) this seems to be a common complaint. A few years back I found that the 2nd floor (everywhere) had difficulty keeping up on hot days. When I reviewed the attic insulation, I found it had settled substantially so we had someone in to seal up the openings aroudn lights and blow in additional insulation. That made a big difference and now the AC can usually keep up, atleast in master bedroom where the thermostat is located.

The AC system is original from 2002. I have done the maintenance replacing relays, condenser fan and capacitors. The furnace blower is starting to make whirring noise that I would attribute to bearings. Nothing that would seem concerning but you cna hear when the blower kicks on
 
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Old 08-11-20, 09:02 AM
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Will test all of the returns and calculate the open area. Most of the return grills are the same design The ones in the closet and jack and jill bathroom are smaller
 
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Old 08-11-20, 05:50 PM
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Forget about free area, measure FPM velocity as you've been doing. You should see an improvement after following my recommendations in #2.

Measuring CFM flow with a flow hood (rent one in your area?) is a much more reliable option than Ak x FPM to determine CFM.

I suspect your system is oversized, but flow is restricted by duct design and/or workmanship issues: SAME OLD. SAME OLD.
 
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Old 08-12-20, 05:55 PM
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Thanks. Will get up there on Sat morning. This is all insulated flex pipe. Just laying on top of the joists and insulation. I am assuming there is at least one T Going to that side of the house so will confirm that there is a damper. I created a log sheet so I can track the air velocities. Tried to do it from memory but more measurements that I expected. I think I saw a difference from shutting off one of the vents in the master bedroom.
Is there a way to easily and cheaply record room temperatures.

Will also document the duct size and configuration. perhaps there will be an option for improving area flow there.
 
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Old 08-12-20, 06:28 PM
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In case it sheds some insight, here is the 2nd floor plan with the vents and returns marked. The furnace/blower is pretty much right above the double doors to the master. not quite to scale. THe 2 bedrooms on the left are about 11x11 or 12x12. The vents are the smaller marks in the rooms. The returns are the larger marks. The returns are all about 8x14. Most of the vents are about 7x11.
 
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Old 08-13-20, 12:47 AM
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The diagram is quite helpful. Just a question on the outlet sizes you've given: They're normally ID'd by duct size, not overall dimension; so is "7x11" a 6x10 in terms of duct size? Same goes for the "8x14": Is it 6x12 duct size? Rectangular/square residential outlet sizes are always even numbers, typically in 2" increments. Double check the outlet sizes and also tell us the size(s) of flex used to connect them.

There are quite a few unnecessary outlets (inside wall at MBR, several of the closets, etc.), and it might be good to remove them provided those remaining have sufficient capacity for the equipment. We'll also need equipment M/N's to check that.

And what's the little room w/o a door at the lower right? Ditto the larger room at lower center w/ two closets.
 
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Old 08-13-20, 05:04 PM
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Some more answer. Easy one first. The room without a door isn't a saferoom <grin> I just forgot to put of door in the diagram, Closet with a supply.

Got up in the attic late this afternoon. The supply lines come off of the plenum and they are suspended in the air all of the way to the vents in the rooms. The main supply lines of the plenum are 10 flexible insulated pipe. There are are several Y' in the supply lines to get to all of the vents. I felt around a couple of the Y for a damper lever but couldn't feel one. It is possible I missed it though. At each Y the pip size gets smaller. THe returns are just laying on the attic floor

THe big find was that the supply line feeding the 2 bedrooms on the left has slipped off of the collar. it was being held in place by the strapping but definitely a major leak. I had a guy in a couple of years ago and he noticed that it had slipped off and at the time repaired it but it definitely pulled off again. THe duct is under alittle tension so there is some force working to pulling it off. I tried to relieve the tension some and use a strap to pull the duct towards the plenum slightly. I will watch it next time I am up there.

So with the duct back in place I measured the velocity at the supplies in the 2 bedrooms and bathroom. THere was a noticable increase in the room a the bottom left. Velocity went from 452 to 515 fpm. The bedroom top left only increased from 375 to 390fpm. The 2 bathroom ducts went from 315/350 to 350/375.

It definitly an improvement but I am not sure it is enough to make the comfort better. Need to monitor for a while.There seems to be alot of vents on the right side compared to the left. The room area on the right is definitely larger (probably large than the diagram indicates) but there are 10 vents on the right and to 4 on the left.
 
  #13  
Old 08-13-20, 11:05 PM
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The flex connection should be made with two wraps of UL 181 tape (must be marked "UL181...") on the core AND then a clamp over all of it, past the bead on the collar. If you want to improve on that, slip a few inches of round duct onto the collar, and fasten to the collar with three screws before starting with the core.

If you want more, give us the info requested in #11.

Good Luck!

BTW: The flex SHOULD be under tension ("fully extended")!
 
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Old 08-13-20, 11:16 PM
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For all you balancers out there: Always check the ductwork before adjusting anything!
 
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Old 08-14-20, 06:25 AM
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Thanks again for all of your comments and suggestions. Still need to get the duct dimension. Hope to do that this weekend.
 
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Old 08-14-20, 03:53 PM
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Here's what needs to be done:
1. Determine the equipment's minimum airflow, thus the request for M/N's.
2. Allocate that on a SF basis to the rooms based on room sizes and exposures.
3. Review outlet/branch duct sizes to see if there are any problems.
4. Develop SOW (Scope of Work) to deal with findings.

Seeing outlets in closets and the unnecessary outlet in the MBR, I'm reminded of a contractor's quaint phrase back in the day: "Getting Rid of the Air" - He knew he'd installed too many tons, and was trying to do what he could to mitigate the effects.
 
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Old 08-17-20, 07:09 PM
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Moderator: Hijack???

I'm having difficulty understanding how we went from a disconnected duct, etc. to a discussion of two vapor barriers on a duct (contraindicated by insulation manufacturers' reps I've spoken with), roofing, etc.

Please help.
 
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Old 08-22-20, 07:02 AM
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Just a final followup on this issue. Not unexpectedly, reconnecting the duct seems to have made a difference. THe far rooms are not perfect but, for now, good enough. Thanks again everyone.
 
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