Return air drop and static pressure

[Wild85]

Hey guys, my home had a airflow specialist come and test the ductwork and make recommendations to the Hvac installer of the home. One recommendation done was to upgrade both supply and return trunks, the supply went from 16x8 and 12x8 to 20x8 and 16x8; the return went from 18x8 and 14x8 to 22x8 and 18x8.

The return drop stayed 24x8 but the drop is no longer anywhere near the center of the 22x8 return. After this work was performed, the static pressure barely dropped, it went from 0.81 to 0.74” on high setting of a Goodman gmss96 60 btu furnace on a 1650’ 2 story.

My question is this, would the return drop not being centered be creating a lot of turbulence? Because it’s clear that somethings keeping the static pressure high. Maximum for the furnace is 0.50”.

Thanks

[pacnw]

Looks like you have a huge return and then it is all restricted into the actual drop.

I am not sure where the increase in size is, but no matter what you increase before the drop, it will still be limited by the drop size.
Also, the best airflow into that filter would be turning vanes or a radius, NOT that hard 90°!!

[Wild85]

The drop is 24x8 so it’s larger than the 22x8 return. I agree and recommended an inner radius with turning vanes to the Hvac people. Do you think the offset drop is an issue? It seems that it may be a problem in my mind.

[Restaurant Mech]

I'd have done a really large transition where the drop comes off the return. Actually scratch that. If I was doing that much work already it would have gotten a much larger drop as well.
Then with a nice big drop the furnace would be fed lot's of air.
The funny thing is that for me return ductwork should always be slightly larger than supply. Air moves really well under positive pressure. It doesn't move all that well under negative pressure. So I avoid negative pressure at almost all costs

[Makeitcold]

How much of that static is on the return side, how much on the supply? Return measured before or after filter and with filter installed and removed? Supply measured in between furnace and evap coil? Full model number of the furnace and evap coil?

[beenthere]

Should be a radius ell at the furnace, and a transition at the 22x8 duct.

[kdean1]

OP, you have focused on size. Fittings and transitions are every bit as important as size. Your guys have neglected those.

[Wild85]

0.41” return static on high. 0.20” pressure drop across coil. There’s lots of turbulence between filter and the 90 on the drop.

[Wild85]

Do you have a photo of what the transition at the 22x8 should look like?

[pacnw]

0.41” return static on high. 0.20” pressure drop across coil. There’s lots of turbulence between filter and the 90 on the drop.

.41" measurement was taken where, before or after the filter?

Unless that is a hole in the bottom sticker on the door, I don't see a test hole AFTER the filter.

[Wild85]

Inside the blower compartment on the left side of the 5” filter rack.

[Wild85]

See photo for return measurement.

[Wild85]

Checked static on high again and get 0.755”

[beenthere]

Do you have a photo of what the transition at the 22x8 should look like?

No I don't.

Imagine a fitting 2x20 at the 22x8 that tapers down to 24x8.

Also, some just run a 20x25 drop to a radius el.

[jbhenergy]

Like this

They all cant be perfect
https://r.tapatalk.com/shareLink/top...ink_source=app


Sent from my iPhone using Tapatalk

[jbhenergy]

Fittings and transitions are more important than size.

How a duct changes direction or size can account for the equivalent of 75’ of duct.


Sent from my iPhone using Tapatalk

[Wild85]

Once the return drop is fixed properly I assume this will allow better performance on the supply side and allow better pull on the return side? Cause right now I’m at around 650 cfm return on a 925 cfm supply.

[Makeitcold]

The blower cant push out what it never brought in so opening up its lungs will help it live a happy, quiet life. It will also drop the blowers electrical draw from where it's running at right now I'm sure, again, helping it lead a long healthy life. You want that return air to be traveling across that filter evenly and at the correct speed so it doesnt just pull the dirt thru the filter and out the other side

[billg]

At the point that the return drop enters the return trunk you have about 120 feet of equivalent resistance, that’s where the most improvement can be made. Doing something like this will help. Then you can look into other things if you still have a problem.

[Wild85]

What would you call this pre made piece?