Duct Work Short Cut on New System

[fstellab]

Hello HVAC folks,

I recently purchased a new 16 SEER 4-Ton Unit SPLIT Heat pump system to replace an old unit the kept breaking down.

I got several quotes for this project. All told me that my current 12" return is not big enough to use with a High SEER system.

The contractor I finally hired was very good, nice neat job, except that the two new returns they put in does not move any air. After the installation they send a quality control person to inspect the job, he found the dead returns.

The Job called for increasing the size of the current return from 12" to 18" and adding two 8" returns. The installer ran all 3 returns to an open box right above the main return grill. Holding a flashlight pointing at the grill, you can see all 3 returns. The main grill was making a lot of noise, ringing, vibrations ..
The QA guy reduced the fan speed, that helped the noise.

But the two smaller returns do not move any air. I did a smoke test with the QA guy and he agreed that this needs to be fixed.

I am pretty sure that the HVAC company will fix this. But I would be very interested in any comments from the Pros on this list.

What should I look for when they come to repair ?
Is this a common way to run ducts ?
Would inline fans help ?

INFORMATION:
House size 2300 Sq FT.
4.0 Ton 16 SEER Goodman Heat Pump Split System
Condenser Model #SSZ160481
Air Handler Blower Model # CAPF4961D6
Honeywell UV Light UV100E
Goodman GSAS Electronic Air Cleaner
Ductwork:
18" main return,
8" return to office(not working)
8" return to outside air (probably not working)

Thanks in advance
-Fred

(fstellab@comcast.net)

[Pete3]

Main return is probably flex duct & undersized.

[RyanHughes]

Main return is probably flex duct & undersized.

Agreed, probably causing too high of a velocity through the main return grille. I can't see from here how the ductwork was run, but wouldn't it make more sense for them to have run all there return flex ducts (3 total) to the air handler/furnace itself? Right now, from what I gather you have one main return flex duct connected to a return box which also contains the main return grille. You also have two smaller flex runs connected to this box, still giving you one main return flex run to the unit. If you can get pictures, they would help.

[dash]

If I understand correctly,they ran 18" flex to a box that is over the main return in the ceiling,then two 8" returns from that box to other return grilles.

If that's the case,that wouldn't be allowed in a new home,it's banned by code,as the two 8" runs will pull very little air.Air follows the path of least resistance,and currently that is thru the return grill,as opposed to the two 8's.The 8' will pull air,when the filter in the grille is pluged.

To remedy this they need to run the 8's back the return plenum,near the air handler, or install a distribution/junction box in the 18 near the existing return box, taking the two 8's out of that and a 16 or 14 to the existing return box.

There's one other way that's easier,depending on the setup,but difficult to describe.Run the 18" into the top of the return box,also the 8's,or near the top on the side of the box.Then install duct board baffles in the box,to limt the amount of air that can be pulled from the grille,this will force air to be pulled from the 8's.


No way to tell from here if any of the duct system is sized correctly.

[BaldLoonie]

All 3 returns to the same grille?

[fstellab]

Thanks Folks for your fast reply's,

I went up in the attic and tried to take some photos .. but they buried the "Grill Box" and the returns under insulation.

The Main grill is a 24" X 18" and the open box above is the same size.
A 18" flex duct goes back to the air handler. The two 8" flex duct are connected right into this box. I know for sure that no air is moving in one
of the returns. The other return is connected to an outside air vent (poor man's ERV), i strongly suspect that one does not retun air as well.

I am not really happy about lowering the fan speed to stop the grill noise, is that a big deal ?

Also, the QA guy told me that I should run the fan constantly to get the best out of the UV light. Is running the all the time an accepted way of operating the air handler ?

Thanks again
-Fred

[fstellab]

Yes the three returns are connected to sheet metal box that is open on the bottom to the main return grill.

There is no DYI items in this setup. I am unable to do that kind of work.

[dash]

Lowering the fan speed to reduce noise is not a good idea,unless it wasn't set correctly when they installed it. Many contractor just guess, testing the static pressure is required to set it ,unless it's a variable speed motor.


UVC does little to treat the air,best installed over the indoor coil,to prevent biofilm and keep the coil clean.The UVC light should be left on 24/7, not the fan,IMHO.

[udarrell]

That Model # CAPF4961D6 is a cased coil in 16-SEER systems it would use a TXV metering device.

It can be used with either a 4 or 5-Ton condenser, in your case a 4-Ton, which requires less airflow; that is somewhat helpful.

I would use way-oversized Return-Air Filter-Grilles on those two Return-Air ducts, with none in the air handler.

Both Return-Air filter grilles must be sized to achieve the same low air velocity & pressure drops with clean filters.

[B]A manual D should be performed on the duct system so it matches the air handler CFM @ 0.5" ESP, then tested while operating so they can work, if need be, to get the ESP at 0.5" when the tested airflow CFM level is correct. They work more efficiently that way. /B] :det: - Darrell

[skippedover]

I usually agree with Dash but in this case I'll make an exception. If the UVL is of high enough output, it does make a difference in the IAQ. Having said that, a high efficiency, variable speed blower will slow down to a crawl when there is no call for heating/cooling and it's in the constant circulation mode. In addition, before I install a UVL I always install a good, high quality electronic air cleaner. They work best when the air is moving slowly so you get the best performance from those when the VS fan is in constant circ mode as well.

As for the ducts, if the installing company did a load analysis, then they should know how much air needs to be moving into and out of each room. And as others have pointed out, air is stupid. It takes the path of least resistance. So if you were stupid, I'm not saying you are but if you were, and you had to go through those ducts, which would you choose? The 18-inch or the 8-inch? And if the 18-inch is 10-feet long and the 8-inch is an additonal 8-feet long, again, which would you choose? Well the air is the same. Unless it's forced to go throug the smaller, longer length, it won't. Dampers will affect the total airflow and negate the additional returns. So I'd put them all the way back to the return plenum and if they're flex duct, it needs to be straight and pulled taught. Otherwise it's a higher resistance and an 8-inch diameter that's slack will give you the equivalent of about a 5-inch pipe when all the resistance is accounted for.

[energy_rater_La]

good advice.
I would add that running fan constantly in hot humid climates reintroduces into the
house the moisture that the coil has condensed. The result is high RH & house always
feels uncomfortable.

I agree that the larger r/a is doing all the work. The smaller flex return ducts should be
installed with flex pulled tight/taunt, it makes a huge difference in air flow. All too often
I see curves & coils of flex, buried in insulation. Flex should be strapped with no more than a 1" sag per 4 feet. In our climate OP insulation covering ducts results in condensation, this is absorbed by the insulation. Strapping flex out of insulation and straightning out the runs will improve air movement in the house.

Best of luck.

[fstellab]

Folks,

Thanks so much for your help.

I showed your reply's to the contractor and he agreed to put a Box right above the return, and run the flex to all three returns. I am not sure why he did not do it that way in the first place, but I can't complain, it was their Quality Control person who inspected the installation who found the problem. I do know that the guys doing the installation wanted real bad to do it all in one day.

Question on the FAN ... I got this really neat Tstat called "Ecobee" .. this Tstat lets me set the min time per hour that the is on. So I could set something like 30 min an hour. I can also control the FAN in the program setting (and I can do all this from a internet link). How about setting the fan on during the day or night. The tstat also can control stage1 and stage2 cooling.. the stage 2 - is a dehumidifier so its controlled but the humidity setting.
the ecobee link: http://www.ecobee.com

[Todd S 2]

Thanks Folks for your fast reply's,

I went up in the attic and tried to take some photos .. but they buried the "Grill Box" and the returns under insulation.

The Main grill is a 24" X 18" and the open box above is the same size.
A 18" flex duct goes back to the air handler. The two 8" flex duct are connected right into this box. I know for sure that no air is moving in one
of the returns. The other return is connected to an outside air vent (poor man's ERV), i strongly suspect that one does not retun air as well.

I am not really happy about lowering the fan speed to stop the grill noise, is that a big deal ?

Also, the QA guy told me that I should run the fan constantly to get the best out of the UV light. Is running the all the time an accepted way of operating the air handler ?

Thanks again
-Fred

Is the 24"x18" a filter grille? Rule of thumb.......2 cfm per sq. in. of the grille.
24x18 equals 432 x 2 equals 864 cfm. A 4 ton system needs 1600 cfm.
Sounds like the company doesn't know what they were/are doing.
18" flex will move about 1400 cfm. Again, short.