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  1. #1
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    Jun 2011
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    Bedroom comfort level

    Don't want this to get into a big discussion like the other thread on returns being added but what would help a room be more comfortable (same temp as rest of house) more registers or return?

    Our house is a ranch with our bedroom being on the short side if looked at the letter "L". So we have three exterior walls. If we leave the door open the room stays the same temp as the rest of the house. If the door is closed it becomes hotter in the summer and colder in the winter. I know wall insulation would help but is a larger register or return the proper fix and which one? The whole house has the same size returns for each room.

    Any other info needed just ask.

    Thanks

  2. #2
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    Aug 2007
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    Northern VA 38 degrees N by 76 degrees W
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    Quote Originally Posted by rk05 View Post
    Don't want this to get into a big discussion like the other thread on returns being added but what would help a room be more comfortable (same temp as rest of house) more registers or return?

    Our house is a ranch with our bedroom being on the short side if looked at the letter "L". So we have three exterior walls. If we leave the door open the room stays the same temp as the rest of the house. If the door is closed it becomes hotter in the summer and colder in the winter. I know wall insulation would help but is a larger register or return the proper fix and which one? The whole house has the same size returns for each room.

    Any other info needed just ask.

    Thanks
    I believe you just answered your own question. By closing the door air will leave the registers and pressurize the room, if you open the door the air can return to the unit. Ad a return if possible if not a transfer grill to communicate with the hall that is large enough to match the CFM of the supply.

  3. #3
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    Is it allowing more air to return to the unit or is it allowing more air to enter the room when the door is open? It could go either way I would think.

    There is a return vent in the hall off the bedrooms but that vent is the same size as our bedroom return vent and only a few feet away from each other (7') or so.

  4. #4
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    Quote Originally Posted by rk05 View Post
    Is it allowing more air to return to the unit or is it allowing more air to enter the room when the door is open? It could go either way I would think.

    There is a return vent in the hall off the bedrooms but that vent is the same size as our bedroom return vent and only a few feet away from each other (7') or so.
    It would be both. If you have a room with 100 cubic feet of air in it and you want to replace it with 100 cubic foot of air, the first 100 needs to leave the room and return to the unit to provide the second 100

  5. #5
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    A person with an manometer and a vane anemometer could answer these questions pretty quickly. I would look into having a whole house energy audit performed. Get the whole house checked out. Could very well be a collection of problems responsible for what is going on in the bedroom.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

  6. #6
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    Quote Originally Posted by tipsrfine View Post
    A person with an manometer and a vane anemometer could answer these questions pretty quickly. I would look into having a whole house energy audit performed. Get the whole house checked out. Could very well be a collection of problems responsible for what is going on in the bedroom.
    I have a manometer but what would I look for the pressure difference with the door open compared to closed? I could borrow a cheap anemometer, I believe my friend who races has one.

    I started a thread that has my results from the Energy Audit I had done. He didn't really discuss the bedroom differences.

  7. #7
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    Quote Originally Posted by rk05 View Post
    I have a manometer but what would I look for the pressure difference with the door open compared to closed? I could borrow a cheap anemometer, I believe my friend who races has one.

    I started a thread that has my results from the Energy Audit I had done. He didn't really discuss the bedroom differences.
    You just close the door to the bedroom, while standing in the hall way and run a hose into the bedroom while your air handler is running. You take a pressure of the bedroom (in reference) to the hall way. You want to see very little pressure difference (in pascals) between the two (no more than a 2.5 pascal difference. A positive reading indicates you have more supply than return in the bedroom.
    The vane anemometer readings will give you a good idea of how many cfms are flowing out of your supply registers & at what velocity & temp. Compare those readings to the rest of your supply registers throughout the home to see if you have huge discrepancies. In other words, if you have 300 cfms flowing from the register in a small room and only 60 from the bedroom registers, you know you have a ballancing issue.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

  8. #8
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    Quote Originally Posted by second opinion View Post
    It would be both. If you have a room with 100 cubic feet of air in it and you want to replace it with 100 cubic foot of air, the first 100 needs to leave the room and return to the unit to provide the second 100
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  9. #9
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    Jan 2009
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    Rather than cutting a hole in the wall, could you also increase the undercut on the door a little more? How much undercut do Pros recommend when you have a central return set-up and 100, 150, or 200 CFM of supply air in that room? I have 2 bedrooms that I have to leave a transome partly open to get enough return air flow. I also thought about adding another ceiling filter grill in at least one of hte two bedroom and that half of the upstairs. The unit is marginal on retun air anyway.

  10. #10
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    Aug 2003
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    At 150 CFM, a 2" x 36" undercut (given that door is 36" wide) will flow 150 CFM at 300 feet per minute (FPM).

    The more you undercut a bedroom door, the less privacy it offers you from the rest of the house. If privacy is not a concern, just leave the door open. If fire safety and/or privacy is a concern, leave the door closed and install a transfer (jumper) duct or dedicated return.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  11. #11
    Join Date
    Jun 2004
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    Useful resources

    A company named Tamarack Technologies used to have a paper titled "The Problem of Pressure". While oriented toward product sales, it had some valuable info including answers to your question. It appears pulled from the net, however I did find this product which might be considered:
    http://www.tamtech.com/userfiles/Per...t_oct_2010.pdf

    It is a novel grille designed to be the functional equivalent of a super sized door undercut, while blocking vision and inhibiting sound getting out. The company also has made some in-wall vents which I admired, for the same purpose.

    Attached is a paper from Building Science Corporation which addresses sizing and air flow in this situation.

    Hope this helps -- Pstu
    Attached Images Attached Images

  12. #12
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    I may have to see about checking out that product PSTU! I know if I were to cut the bottom of the door I would have the cats paws under there with them trying to get in!

    Before I do that though I should see what kind of difference it makes on the room with haveing the door cracked enough to give me the same area as that product. If there isn't a measured and felt difference then no need to bother with it.

  13. #13
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    May 2004
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    south louisiana
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    you also have to consider that interior hollow core doors have
    a 2" solid piece at top and botton of the door.
    this minimizes the size of the undercut.

    a 1" undercut will return air from one supply grill.
    if you have more, you need a dedicated way for air to
    return.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

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