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

[2manyrocks]

You could possibly buy some thicker gal. sheet metal at a HVAC supplier or a cut off from a sheet metal shop. Some HVAC suppliers won't sell to anyone who doesn't have an HVAC license, though but some will.

I was thinking that you'd remove the transition, fab and screw in the new diverter, and then reinstall the transition using foil tape.

 

[2manyrocks]

Interesting you say that. I have said the same thing. I am surprised someone hasn’t come up with a smart home HVAC setup that is “always on” but blowing low and slow.

Inverter heat pump mini split systems are essentially designed to do this and vary the compressor output depending on the heat/cooling load on the system. The indoor air handler for many mini splits is quieter than a normal home refrigerator. They are very suitable for open living room spaces, but the blowers on them aren't generally powerful enough to blow air through a duct system that you'd normally use for heating and cooling bedrooms and bathrooms. Part of their energy efficiency is because they aren't having to push air through a duct system.

Which brings us back to the OP's air handler which is having to push air through a duct system. Air weighs 14.7 pounds per square inch at sea level. This means there is a respectable amount of weight to be moved in any HVAC duct system by the air handler. So it isn't surprising that there can be noise associated with air handlers because of the amount of air they are moving.

 

[Sigarms]

I went to Lowes, and bought a 24"x36" piece of galvanized sheet.
It is so thin, (WAY thinner than 30 gauge) I am sure I could cut it with a pair of scissors. (I have WISS snips if necessary.)

If you haven't cut the metal yet, I'd take it back and cruise a local HVAC shop and see if they have a scrap piece of 26 or 24 gauge laying around. Don't know if I'd want 30 gauge or thinner in an airflow. Most shops will have break and it will be nothing for them to put a crisp 90 degree edge on it.

That said, what most local guys do if they don't have a metal shop is use a local custom metal shop. If you can find one, generally the pricing is the same, and do it right the last time. Measure the duct opening to the plenum opening along with the distance, and it should fit like a glove. Heck, they should be able to either wrap or line it for you as well.

The biggest question because this could be a airflow issue is was a start up sheet ever completed on start up with the pertinent info of static pressure and CFM's recorded on what the system is doing vs what is should be doing?

Most times if a guy has a airflow issue and you ask him what the CFM's and static pressure are, the general response is "GOOD!" but dang, he'll have his gauge readings all ready.

 

[2manyrocks]

If you have a metal shop fab a new transition to the proper dimensions, it's going to have the best airflow because it won't have all the additional screws and edges inside the transition that would be involved with adding a diverter. You also avoid the risk that the diverter won't fit, rattle or have air leakage. If the shop fabs it up wrong, then they don't have the excuse that they were making something to salvage someone else's prior foul up.

 

[ponytug]

I do have some industrial gauge siding left from building my shed,, maybe 22 gauge, or even possibly thicker
I could cut a piece of that, and pop rivet the siding to the back of the shaped block off panel,

Smooth on the air side, ribbed in the void area,, Hmmm,,,
If I can not easily get in the plenum to install screws, maybe a strong magnet could hold the block off in place??

Just screw it in from the outside. It is quite common. To put it in, you will need a way to align and support the inside piece while fastening it, which will mean disassembling the existing plenum to get access, either from on top or below. It is not going to be quick either way.

However, I do go back to my original advice and suggest that you just get a more talented HVAC person in to fix it.

All the best,

Peter

 

[ultrarunner]

Local HVAC with sheet metal fab was dirt cheap making my plenums and heavier metal.

Last one was just before Thanksgiving… I went in and he said it would be ready Monday afternoon…

I said I will let everyone coming to Thanksgiving to wear sweaters.

The owner said can I come back in an hour…?

Did a beautiful job and when I said it was heavy he said less problems…

 

[ponytug]

Inverter heat pump mini split systems are essentially designed to do this and vary the compressor output depending on the heat/cooling load on the system. The indoor air handler for many mini splits is quieter than a normal home refrigerator. They are very suitable for open living room spaces, but the blowers on them aren't generally powerful enough to blow air through a duct system that you'd normally use for heating and cooling bedrooms and bathrooms. Part of their energy efficiency is because they aren't having to push air through a duct system.

Which brings us back to the OP's air handler which is having to push air through a duct system. Air weighs 14.7 pounds per square inch at sea level. This means there is a respectable amount of weight to be moved in any HVAC duct system by the air handler. So it isn't surprising that there can be noise associated with air handlers because of the amount of air they are moving.

Ok, I agree with the first paragraph.

However, the second one is a little garbled. I am sure that you meant to write about the weight or mass of air in the system.

Yes, the pressure of air at sea level is 14.7 pounds per square inch, but that is the weight of all the air above one square inch to the end of the atmosphere hundreds of miles up. What the OP needs to worry about is the mass/weight in the volume of air in their system. The density of air at sea level under standard conditions is only 0.0765lbs/cu.ft. of volume, so air handlers aren't moving much weight (mass). That is why furnace fan motors are so small. There isn't much actual work being done.

The small pressure difference between inside the plenum versus the outside over the large area of a plenum wall isn't zero, and that's why small variations in turbulence move the whole wall, generating rumbles. Three inches of water difference is about a tenth of a pound per square inch, which is probably close to the base pressure on the plenum walls. If the turbulence generates a tenth of that, that means the turbulence would generate about 1.4lbs/sq.ft., more than enough to flex thin sheet metal. Hence, @CADplans' rumblies.

All the best,

Peter

 

[ultrarunner]

Want to burn out a blower or create backdraft just run with obstructed filter.

Last 3 blowers replaced all had plugged filters.

In to the point of leaving out the filter and sealing the access slot at one rental…

It’s the old story… you can buy a man a case of filters and show him how easy it is to change but will he do it???

Christmas I was asked to look at a furnace going “Boom” at a neighbors…

It was as simple as changing the filter something her husband always did until he passed away 3 years ago…

 

[Midniteoyl]

Want to burn out a blower or create backdraft just run with obstructed filter.

Last 3 blowers replaced all had plugged filters.

In to the point of leaving out the filter and sealing the access slot at one rental…

It’s the old story… you can buy a man a case of filters and show him how easy it is to change but will he do it???

Christmas I was asked to look at a furnace going “Boom” at a neighbors…

It was as simple as changing the filter something her husband always did until he passed away 3 years ago…

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.

 

[Raul-02]

The noise of the turbulence is carried by the ductwork to every room in the house.

I'd cut the wall open with a zip disk and make a port in the plenum through which I could install a couple of different devices to redirect air. If it didn't work it's a simple fix seal the opening with pop rivets or sheet metal screws.
I'm thinking you've got nothing to lose, there's no warranty to void and a simple airfoil or some inline vanes to encourage laminar flow might do the job.