Return Air Grilles: What is High Flow Return Air Grille?
What's the difference between the two?
In residential households, there are two different kinds of return filter grilles. There is a fixed bar-style grille, and a stamped face grille. A high flow return grille (also known as a fixed bar return grille) is a more aerodynamic type of return grille than a stamped face return grille. The louvers on a fixed bar return grille are spaced further apart and more aerodynamically designed than those on a stamped face grille. A high flow return grille (also known as a fixed bar-style return grille) has a larger open area to allow wind to flow through the grille.
Why Does This Matter?
We think about this for several reasons.
1. Lower static pressure to save money and extend the life of appliances.
2. Less noise—have you ever heard a whistling sound or a noise from the return grille while the equipment is running? The noise would be eliminated if you install correctly sized fixed bar return air grilles.
3. Improved ventilation- a return grille with a wide effective surface area offers more comfort in your house.
Return Air Routes (Transfer Grilles)
Tamarack retires Air Pathways (RAPs) are one-of-a-kind transition grilles that preserve sufficient airflow between rooms while also eliminating pressure imbalances. Our RAPs are a simple and economical way to enhance indoor wind quality, remove hot and cold spots in spaces, and reduce the burden on air conditioning systems. Most notably, installing RAPs increases energy efficiency and saves money on both cooling and heating for homeowners.
Concerning Return Air Pathways (Raps)
To provide conditioned air to any room in a building, most HVAC contractors mount ducts and registers. However, they always fail to provide a sufficient return-air route from each room to the furnace. In several households, return-air transfer grilles are not installed in every room. Instead, houses would have a single wide return-air grille that serves the entire house in a central corridor or living room. This means that all of the wind needed by the home's forced-air system must be drawn through the single grille before being heated or cooled by the furnace. As a consequence, the atmospheric flow is disturbed. As a result, there are inconsistencies in room temperatures, higher electricity levels, and moisture issues in toilets.
Using through-wall and in-door switch grilles is a convenient and economical alternative in these situations. Retire Air Pathways (or RAPs for short) are Tamarack Brand transition grilles that provide a channel for wind to flow from one space to the next. Tamarack RAPs have an internal baffle material that prevents improved light and sound propagation through the vent/grille.
RAG-X (Return Air Grille) Ask Now
Polyaire's RAG-X is a full retire Air assembly made of injection-molded high-strength plastic for easier installation, service, and maintenance.
When opposed to conventional grilles, the RAG-X one-piece construction has a dramatically improved look. It is faster and cheaper to use, and it saves time.
Characteristics:
• Dust reduction is aided by the use of a three-filter system.
• Low-Static High-Efficiency Filter
• A black filter is used to minimize the appearance of see-through.
• Cleaning or replacing the filter and grille is easy.
• Wide open space for effective airflow in a quiet manner.
Additional functions include:
• Grille release clips are shielded from view but are still readily visible. • Aluminium Filter Frame
• For further convenience, the grille opening may be reversed.
• Eggcrate grille style is appealing.
• Retire air box that is rigid.
• Easy to install in only a few clips.
• Clip-on reducers handle a wide variety of vent sizes.
Features of the installation:
• Oval Connector, 750 x 450/1 x 400mm
• Oval Connector, 900 x 500/2 x 400mm
• Round Connector 1195 x 595/2 x 400mm
• One-piece rigid shell for simple assembly.
• Use a regular Fast Repair Spigot or Reducer to connect the duct quickly and efficiently. (Affix the Duct to the collar before clipping it to the roof.)
• With wing nut modification, it's simple to mount to the ceiling (No tools needed).
• Long-lasting metal wire clips that don't sag.
• The filter grille can be used in any direction and swings out for quick washing.
• Front grille clips have a constructive locking feature and are convenient to use.
• Plenty of open space.
• A basic slide in/out filter is included.
• Egg crate grille shape makes for more efficient airflow.
Fabrication:
• All composite for long life, low noise, and corrosion/rust resistance.
• One piece molded retire wind box for strength, no leakage, and low noise.
• Easy-to-use reversible grille
• Tri-Filter is detachable.
• Filter with an aluminum frame.
The Value of Return Air Grille in the Duct Dynasty
Return placement, contrary to common opinion, has very little impact on wind currents in a room. When I make this comment in class, a lot of students either see red or think I'm nuts. It goes against what most guys have been told, and I should know because I used to think returns had a big effect on air movement.
Regardless of the volume of air passing through the return grille, the wind patterns of supply registers scarcely affect the air patterns of supply registers. The example below indicates that their influence is limited to a short distance from the grille's ears.
About the fact that returns have no effect on air patterns, it's a smart idea to put them somewhere where they won't be specifically affected by source discharge wind, enabling them to short circuit the mixing operation with room air. We were called in years ago to run an air diagnostic test on several gas-fired units in an attic in a church. For a drop-down ceiling, the return grilles and supply diffusers were typical issue scale 2 X 2.
One of the things we found when checking these systems during the heating period was that the return grille temperatures were rapidly increasing to over 90 degrees, while the room temperatures were just 70 degrees, which was incredibly unpleasant. We quickly found that the supply wind was not being discharged far enough away from the ceiling due to poor airflow from the supply diffusers. The hot air, which was now having difficulty getting down from the dome, was simply flowing over the drop-down ceiling tiles and recirculating into the return, which was about 5 tiles across.
Size of the Return Grille
The return side of the duct system is where the bulk of duct system problems occur. The grilles that are connected to these ducts, like the traditional return duct device, are undersized.
To minimize noise through a return grille, the speed of the air passing through it should be maintained between 300 and 500 FPM (Feet per Minute). A grille that crosses this velocity spectrum is easy to hear when it is normally followed by a loud noise. Sometimes, this noise will be in the shape of a whistle or a low-pitched hum that will reverberate while the HVAC system's fan is turned on. An anemometer would be used to check the speed of wind passing through the return grille.
The optimum speed of air passing through the grille does not exceed 400 FPM for return filter grilles with the filter positioned behind the grille face. Examine the technical data for the filter grille you're thinking while sizing it. Find a CFM value that is equal to or marginally higher than what you need in the 400 FPM column. The filter grille size that corresponds to that value is the one you'll need. When engineering data is unavailable, an estimated rule of thumb is to multiply the filter grille area in square inches by 2 CFM per square inch. This can hold the filter grille's face velocity below 400 FPM. For a 2 ton unit rated to shift 800 CFM, this rule of thumb approach will need a 20 X 20 return filter grille. On a 2 ton unit, how much do you see a 20 X 20 return filter grille? Not often enough, to be sure.
Transfer Ducts with Return Grilles
It's important to use a grille with very low airflow resistance by using return grilles with transfer ducts in central return applications to reduce room pressures. When a door is locked, most guys just slap on any grille that will match the rugged opening, forgetting that normal pressure variations would cause air to return to the return. The use of stamped face grilles in this application will not yield the desired results. Instead, a commercial-grade grille will give you great results.
I'm sure all of you who read this have heard horror stories about undersized return grilles. I'd like to hear them and, if possible, see pictures!