Home Furnace Air Handler Plenum Design help,, Anyone A GURU??

[Midniteoyl]

Agreed.. I'd be real tempted to cut a slit (dremel) in the transition and slide a piece of sheet metal in there to test before taking it all apart. Just seal the slit with tape if it doesn't work out.

 

[CADplans]

MiL had a failure once. I went over to check and found the filter was so bad that it collapsed and got sucked into the fan.

Back in the 1960's, they used to sell an air filter with a built in "whistle",,
when the filter needed changed, the whistle would start howling,, indicating the filter was clogged.

Either change the filter, or you did not sleep at night. LOL!! `~`

 

[2manyrocks]

If the OP cuts into the sidewall of the transition, it will weaken it and it becomes another possible source of air leaks. grinding dust will also get in the air handler.

 

[jaxs]

If the OP cuts into the sidewall of the transition, it will weaken it and it becomes another possible source of air leaks. grinding dust will also get in the air handler.

Compared to most other recommendations ,the slit should be simple to execute and repair. I would believe 99% of dust created with grinder will fall and become trapped between metal shell and interior insulation. Using only half the tools needed for other solutions,fabercating a witch's hat shaped strip and pop-riviting it over slit should be a breeze.

 

[CADplans]

I think I can remove the foil tape, then remove the four drive cleats, and then be able to remove the flexible duct coupling.
If that gives me enough room possibly I can get the block off adapter through the resultant opening.

Otherwise, the plenum will come off.

I hate to remove the plenum, there is a LOT of some "mastic" type black sealant connecting the plenum to the air handler.

I can not bring myself to do anything that will drop metal shards into the air handler,,,

 

[ultrarunner]

I use a nibbler for tight spots and except for the drilled start hole no metal falling inside

An old time trick is to put a gob of heavy grease on the bit and a lot of the chips will stick to the grease.

 

[Sigarms]

I'd suggest before you go tearing anything apart, know the static pressure and CFM's the system is producing, and verify the system is doing what it's supposed to be doing and not make an assumption it's air turbulence (yes, easy assumption to make, but it could potentially save another headache). I could be wrong, but I don't think the OP has given that information.

 

[CADplans]

I'd suggest before you go tearing anything apart, know the static pressure and CFM's the system is producing, and verify the system is doing what it's supposed to be doing and not make an assumption it's air turbulence (yes, easy assumption to make, but it could potentially save another headache). I could be wrong, but I don't think the OP has given that information.

As a precursor to answering this question,,
a) I have talked to over 6 local HVAC companies.
b) I have personally talked to over 20 HVAC technicians.

My conclusion is that the local HVAC companies can
A) do some tin knocking,
B) physically place new components.
C) silver solder copper lines.
D) get operating pressure of the HVAC gas in the system close enough.
I also feel that the local HVAC companies,
E) have almost zero understanding of the NEC (national electrical code)
F) have ZERO intention of reading the installation manual
G) have enough knowledge to do a basic thermostat install,
BUT, have almost zero capability to customize thermostat settings for an individual install.


True, I have not given the CFM's and static pressure.

If I use the previous system as a baseline, (it worked perfectly from 1977 to 2020)

1) the CFM air flow of the new system appears to be identical to the old system, or very close.
2) the tonnage rating of the two systems are identical.
3) the comfort level of the new system is adequate, not perfect, but, the old one was not perfect either.
4) in about 1.5 years of operation, no occurrences such as unit freeze-up has occurred.

So, based on my satisfaction with the new system, my only major drawback is the noise.

I am sure I could get the CFM readings of the system, with a little YouTube help, and buy some equipment.
I could build an adequate manometer, and get the pressure.

Since the big issue that I see is the noise, and my hand (felt vibration) has isolated the noise to the plenum,,
I feel that the easy fix is a suitable block-off transition in the plenum.

The only reason I have not started tearing out the plenum is that I have one stumbling block that should be resolved within a week.

So, I started this thread to help me get my ducks (NOT DUCTS!! LOL!) in a row,
for hopefully finding the easiest way to install the transition.

If the air handler were located directly under the "T" fitting that is part of the original ductwork, I would get the plenum remade.
The MAJOR problem is that the plenum also has a 3.5" sideways offset.
The air handler can not be easily moved, that plenum would be almost impossible to rebuild from simply giving a guy dimensions.
Therefore, hopefully, I will be able to install a block-off plate.

If I install the block-off, and the noise is resolved, I would happily pay a duct company to come out and make a new plenum correctly.
The problem is ,, I am POSITIVE that a local company will end up charging north of $500 to make that new plenum.

That $500 price is based on the new price of labor, transportation times, figuring in at least 3 visits to get it right.

If I do not tell them EXACTLY what to do,, I will end up with a new plenum similar to the old one.
It will connect "A" to "B",, but it will not follow any rules of plenum construction.

That is my problem, in a nutshell,,,

 

[2manyrocks]

You might could slice through the mastic with a scraper blade in a multitool. This one is actually a pretty good multitool for $15. https://www.harborfreight.com/16-amp-single-speed-oscillating-multi-tool-62866.html I don't think it comes with the blade which you can get for $8.00. https://www.harborfreight.com/blade-set-for-oscillating-multi-tools-3-pc-61827.html The toothed blade could cut through the duct, and I wouldn't use it.

Wear ear protection because the tool is loud.

 

[Sigarms]

have ZERO intention of reading the installation manual

I am sure I could get the CFM readings of the system, with a little YouTube help, and buy some equipment.
I could build an adequate manometer, and get the pressure.


That is my problem, in a nutshell,,,

You make great points.

ANY decent service tech you talked to should have been able to get your SP and CFM's accurately. What decent HVAC service tech doesn't have a manometer and pitot probes?

And yes, I'm the biggest idiot out there, however, I always read instructions. There is always something different on page 15, 3rd paragraph down that will cause you a lot of headaches if you don't do it. You can always tell a good HVAC company when they put in a new brand and the guys come in early to go over the install manual LOL

I've just found in my experience, having hard accurate numbers for your readings helps you eliminate what the issue isn't. This is why even on a service call, a good tech will not only get your pressure readings, but also your air flow readings. The irony is airflow can affect your pressures.

 

[2manyrocks]

I would guess air flow measurements would be okay, but I've yet to see an HVAC tech come out with a sound level meter or measure audio frequency response for rumble caused by not making a smooth transition from the air handler outlet to the duct system.

It just looks like the installer was concerned with trying to make an awkward transition at an angle from the air handler to the ductwork. So he went with a transition sized to the case instead of the outlet. The system evidently works, but CADplans is tired of the noise because he's the one that has had to live with it.

 

[ultrarunner]

Problem is it is ongoing day in and day out for decades...

Seen more than one new install with a do over... and the customer was right.

The system I put in my brothers was about as quiet as could be... it was 100% new ad previously only a wall furnace and window AC.

His neighbor had a 12k similar but it was like gale force wind and loud like a vacuum in the next room

Installer used much smaller duct work and one speed blower and that was just the start.

I have some commercial transitions not made with metal but more like a rubber coated canvas material that can flex and it is very quiet...

 

[CADplans]

OK, I have taken the "next step" in my heat pump install saga,,

I removed the plenum, which was easier than I thought it would be.

The flat top surface of the air handler can be seen here.
I decided to install an angled block off piece of sheet metal.

Since the plenum was removed, and the block off would be installed while the plenum was on the floor, the concern about drilling chips getting into the air handler was eliminated.

The last time I made a modification to a plenum was 50 years and 4 months ago.
(I remember the date accurately, it was when I went on active duty with the US Navy.)

So, after pulling up some files from my memory bank,, I cut, then bent, then installed the block off.
Here is a pic of it installed, ready to replace the flexible joint.

I simply bolted the block off to the insulated interior of the plenum.
I used 10-32 bolts, with washers and double locking nuts. I did not want the bolts to vibrate loose.

Then the flexible joint was re-installed,,

After the two drive clips were installed, I retaped all the joints,

The unit is now 90% quieter!! SUCCESS!! `~`

With the noise issue resolved, I still have a few other issues.
I need to replace the 220 volt wiring to the air handler, and purchase the correct size breakers.

 

[ultrarunner]

Thank you for posting the results...!

 

[ponytug]

Great memory banks! Nice job, and I am really glad it solved your problem. (Is 90% good enough?)

All the best,

Peter

 

[CADplans]

I started a new thread to help investigate a startup issue with the new heat pump,,

Heat Pump Startup Makes The Lights Flicker,,, Is That OK??​

Heat Pump Startup Makes The Lights Flicker,,, Is That OK??

Well, we have a new heat pump, I watched the tech monitor the running amps,, only about 17 amps. The compressor is a "screw type" rather than a piston of the old days,, The screw type should have lower startup amp demand.. no pistons to get moving,, ? What surprises us, is that the lights will...

www.tractorbynet.com

 

[m1garand762]

Make sure the motor is set for 350-400cfm per ton cooling the ahu should have an ecm motor. The dip switches should be checked and also make sure that it’s set to 2.5 tons that is all set through the board that funds the motor