Sizing Hvac return

[Acuratechva]

Handler inlet vs Hvac return size

Hey so i am having some issues understanding return grille sizing. Fully aware that you must return more air than supply, cant remember the number but that not important here. Dont worry about per ton or any other info this is irrelevant here.

This instant i am researching the handler is on top of return and there is no duct work.

In terms of physical dimensions Goodman uses same air handlers for most systems. And they all have the same return/inlet which is 14x19 opening.

If calculations require 400sq in then , someone please explain to me what good it putting a say 20x20 return box/grille on a handler that will still have the bottle neck of 14x19


I am not physics anything so maybe this is where i am getting lost.

 

[Jim greengo]

What is it tied into?

 

[metlmunchr]

Return filter grilles are sized based on required filter velocity and not on the size of the return opening in the unit.

 

[jlrut]

Because the grille is restrictive and will howl if you undersize it. A 14*19 opening has no restrictive louvers. So for a 400 sq" I assume you are running a 2-ton air handler?

 

[Ohmthis]

14x19 may be sufficient for the air that the air handler moves. Keep in mind return grill and filter grills are different. The filter produces a restriction, so you want it sized for the least amount of restrictions possible and still filter the air. The width is important too. A filter 14x14x1 has less pleat (I’m using pleated filters in this example) surface area then a 14x14x4 filter. Obviously if a 16x20 filter is required for the least amount (there is an actual measurement in the restriction that is looked for in inches water column) restriction then a filter rack or grill the size of the filter is required. I hope this helps!

 

[jkeyser14]

You need a larger opening because you need a larger filter area to not starve your fan of air. Filters create huge pressure drops. The larger/deeper the filter the better.

 

[nsula_country]

Also if face velocity is too high, the filter cannot filter all particles. Some will bypass through. Residential filters should not have a face velocity over 300 fpm.

Required Equipment Airflow (CFM) ÷ Filter Velocity = Square Feet of Filter Needed

CT