Heating, Air Conditioning, Fridge, HVAC/Bedroom AC Return
QUESTION: Hi Jim,
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:
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?
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?
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!
I don't know what the the building code is in your area as far as useing flex duct on the return, or if you even care?
Also I dont know what size/area carries the return air from the 20X20 opening?
Do you keep the bed room doors open or closed?
---------- FOLLOW-UP ----------
QUESTION: Hi Jim,
I crawled up in the 20 x 20 opening to measure the rectangular solid duct that runs from the return to the air handler today. The duct is 12 inches high and 19 inches wide inside diameter.
While up in that duct which is an R4 rating, the inside wall of the ductboard was rather warm! I am wondering if I can beef up that R4 value by using that 2 inch thick owens pink foam board to layer the return ducting in the attic so the hot attic air does not infiltrate so much??
I keep the door open, but the room still does not cool down till 1 or 2 am.
Flex or hard ducting in my area does not matter per code. Someone told me that flexducting comes in 25 foot lengths which must be cut down to size. if that is true, it would be cheaper to buy a 4 foot length of solid rectangular 8 inch duct?
Thanks for your help, Jim!
Rule of thumb:
One ton of cooling for 400 sq. feet that you want to cool, + or - depending conditions, windows, insulation, shade, outside temp. construction.
You need at least 200 square inches of free area for return air to flow through,
The free area of a 20x20 diffuser is 200 in.
The area of a clean, new filter in the diffuser is 200 inches, dirty, used filter lessens the area.
You can shut the supply diffusers somewhat in the stronger flow areas to force more to the weaker areas, any thing you can do to supply more return will help.
I don't know what your air handler unit consists of?