Heating, Air Conditioning, Fridge, HVAC/Bedroom AC Return

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QUESTION: Hi Joe,

I have a 1350 square foot brick ranch house with a 2 ton Reehm AC compressor outside and air handler in attic. There is a single air return (20 inch x 20 inch opening) for the entire house in the hallway which is in the western end of the house.

Each bedroom on the western end of the house has a single air supply register in the center of the room ceiling. Both of these rooms become much warmer than the rest of the house. They do not cool down until about 1 or 2 am in the morning. The living room, where the thermostat is located, could be 72 degrees while the master bedroom is 78 degrees at 9 pm.

My master bedroom (13 feet x 12 feet) has an 8 inch flexible duct that is 24 feet long going into the center of the ceiling of this room. The guest bedroom (10.5 x 10.5 feet). The single air return in the hallway is outside the doorway of both of these rooms.

To better cool the master bedroom, I plan to install an 8 inch duct from the ceiling into the return box that has a R4 value in the attic. The bedroom return will be a four foot long duct from the bedroom ceiling grill box to the return box in the attic.

Here are my questions:
First:
Can I install flexible duct as a return from the master bedroom ceiling into the return box in the attic or do I need to use a rigid duct since air handler will be sucking air out of the bedroom through that ductwork?

Second:
I want to put a filter in the return grill I put in the bedroom ceiling. Problem is I can't find a 8 inch by 8 inch filter. Since there is a filter in the 20 inch x 20 inch grill in the hallway, I don't want this to be unfiltered. What suggestions do you have to filter this bedroom duct?

Third:
How much will connecting this 8 inch bedroom return duct into the main return box in the attic reduce the negative air draw into the air handler for the rest of the house?

Thank you for your help!

Appreciatively,

Mike

ANSWER: Mike,

Yes flex can be used for your return in the bedroom stretch it out for maximum air flow, certainly ridged would be better. Flex is sold in 25 ' length so it probably cost less using ridged, which is sold in different length starting at 2' and up. As far filter you would be better off buying a standard size and cut as needed. I don't personally don't  think installing this return duct will adversely affect your other returns

---------- FOLLOW-UP ----------

QUESTION: Hi Joe,

Thanks for the suggestion about stretching the flex to enable max air flow in the new AC return. The flex is MUCH less expensive than rigid. A couple more questions came to me as I read your answer and also contacted HVAC suppliers.

1. With regard to the flex duct, there will be a 90 degree bend formed after the flex duct goes from a vertical direction to horizontal. How much concern is there about that being a choke point on that bend? How do I address that choke point potential?

2. If I go with rigid duct, how does one address the 90 degree bend from the vertical part of the duct run and the horizontal part of the duct run to the main return through the attic? I called an APR HVAC supplier and he says no one makes a rigid elbow?

3. The APR guy also said no on makes a rectangular collar for the return box in the attic. They only sell circular ones. How does one attach a rigid square duct to the main return box duct in the attic without a collar?

Thank you for your help!

Best Regards,

Mike

Answer
Mike,

Make a wide sweep 90 if you go with flex, if you use ridged they certainly make them in 90 degree , it's actually adjustable from 90 to almost straight. Even Lowes Home Depot has them.

You can have a custom square duct take off transition piece made , for your return, or buy a square to round transition and then run a small piece of flex to the return duct, finishing with a round take off collar.

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Joe

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40+ years diversified experience.An HVAC/Refrigeration Self Employed Contractor since 1986. NATE Certifield. Answer questions pertaining to Residential and Commercial Air Conditioning , Warm Air Heating, Heat Pump systems.Mechanical and Electrical troubleshooting of these systems.Be as detailed as possible when describing problem.Packaged unit or split systems.No appliance questions.

Experience

Installation and Troubleshooting, Mechanical and Electrical, in following areas, Refrigeration ( Walk In and Reach In Coolers and Freezers ) Commercial Roof Top and Packaged Heating/Cooling ( Natural Gas,Propane, Electric, and Heat Pumps ) Computer Room Air Conditoning Systems,Commercial Residential Packaged and Split Systems Air Conditoning and Heat Pumps.Warm Air Oil , Natural and Propane Gas Heating systems.

Education/Credentials
Graduated from Private Technical School in 1975. An HVAC/Refrigeration Contractor . Have Unlimited Heating/Piping and Cooling Contractor License.Limited Sheetmetal Contractors License.NATE Certifield. York Certifield Master Heat Pump Technician 1986. Served 33 years combination Active Duty Air Force , Air Force Reserves and Air National Guard in the HVAC/Refrigeration Shop/Mechanical Shop. Troubleshooting/Installing HVAC/Refrigeration Equiptment Worldwide. Retiring in 2003 as a Senior NCO ,and a Mechanical Superintendent.

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