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Community and Q&A

Floor supply register air stays low before being sucked up by return register

jeffwatson | Posted in General Questions on

The supply & return registers are on the floors (hardwood) located along opposite walls from one another.

Supply register is along an exterior wall under a window, return along an interior wall. Separation is 9 feet. Basic, 9x12ft rectangular room.

We’ve always had a problem with this room not cooling or heating as well as the others and I just noticed something recently about the airflow within this room –

When the A/C is on, there’s a decent velocity of conditioned air coming out of the supply if my hand is a couple inches from the register. However, tracing the air flow as best as I can as it comes out, it feels like the conditioned air stays low to the ground & shoots horizontally directly towards the return register.

In this room, I feel cold air from the waist down as I walk in-between the supply/return register path. Outside of that path and from the waist-up – nothing.

This is in comparison to other rooms, where it feels like the air comes out “straight up” and “falls down” & conditions the whole area.

What causes this? My guess is too powerful of a return but nothing I’ve read ever seems to mention dampening return registers.

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  1. GBA Editor
    Martin Holladay | | #1

    One possible explanation has to do with the type of floor register. Some floor registers are designed to "throw" the air in a certain direction; others have adjustable louvers that direct the flow.

    Examine the louvers on your floor registers. If necessary, replace them with new registers designed to direct the air flow straight up.

  2. jeffwatson | | #2

    Martin, all floor supply registers are the same style within the house - what I've come to learn are "base board" style, 48" long (save for some some 24"s in the bathroom/kitchen). The actual ducts are rectangular, about 8-10 inches wide. Similar to the pics in this guy's post (not mine):

    This is the only room exhibiting this "low to the floor" phenomenon.

  3. GBA Editor
    Martin Holladay | | #3

    It's hard to assess what's going on without a site visit.

    For a forced-air HVAC system to work properly:

    1. You need a house with a good thermal envelope. You don't want air leaks that allow infiltration or exfiltration -- leaky houses can easily become pressurized or depressurized by a forced-air system.

    2. You want a well-designed duct system that supplies the proper airflow (cfm) to each room -- neither too much nor too little airflow.

    3. You want a well-designed return air system that pulls air evenly from each room that has a supply register. Return-air grilles and return-air ducts must be properly sized to work well.

    If your house doesn't have these features, the problems need to be corrected.

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