Return Air Grill - Page 2
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  1. #14
    Join Date
    May 2012
    Location
    San Diego, CA
    Posts
    352
    Yeah, your supply temperature is good and 3 tons should be pretty close to what your need... so dirty coils doesn't seem as likely...

    The 18 F difference between return and supply means your house is around 75 F.... That is pretty normal design temperature too. How cold do you set your thermostat? How old is your house?
    You can call me Sam

    It should be a crime to be a mechanical engineer in San Diego
    Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

  2. #15
    Join Date
    Jan 2012
    Location
    indy
    Posts
    471
    24x14 with no duct ya might be noisy but should be enough area, a 4" filter would help too, some of those 3m menards filters are tooooo restrictive for a system that isnt already perfect (which not to many are) the side of a furnace cut out is 24-14 and the only time I go bigger is when its a 5ton use bottom or two sides. Adding another can never hurt, helps it breath if you will but cost of install and more filters is the only downfall...

  3. #16
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,584
    Check the airflow with the door to the AH closed and then check it with the door open.

    That is an easy way to determine if the unit is getting enough return air.

    I agree with Genduct that even though the grille is too small, your AH is getting air (maybe enough or not) through the nooks and crannies.

    Try the above and let us know. P.S. How many suppies are in the home?

  4. #17
    Join Date
    Jun 2010
    Posts
    16
    Quote Originally Posted by hcong View Post
    Yeah, your supply temperature is good and 3 tons should be pretty close to what your need... so dirty coils doesn't seem as likely...

    The 18 F difference between return and supply means your house is around 75 F.... That is pretty normal design temperature too. How cold do you set your thermostat? How old is your house?
    Now don't laugh, but we like to keep it around 70F throughout the day, and on many days our system will "maintain" this temperature but if we decide to let it get to 72F for some reason, then the unit will not typically bring the temperature in the house back down to 70F until the outside temperature has significantly dropped.

    Our house (and unit) is 5 years old. We bought both completely new. We are the only homeowners of this house, and the unit was installed the day before we moved in.

  5. #18
    Join Date
    May 2012
    Location
    San Diego, CA
    Posts
    352
    Quote Originally Posted by tlhiv View Post
    I guess I would like to know if adding another return grill and filter (same size) on an adjacent wall if I could expect more cool air to enter through the supply registers and thus cool the rooms faster. As it stands now, my unit does not power cycle at all throughout the day if the temperature is more than about 85F - 90F. I have been told by more than one professional that a 3 ton unit should be sufficient for my house, but my friend (who is also a professional) suggested that my return air may be too small. I'm wondering if I increased it whether I could supply a larger volume of the same temperature (cold) air into the house (thus cooling the house better than it currently does).
    The pressure drop over the return grille is probably around 0.06 w.c. (http://www.krueger-hvac.com/ecatalog...px?fileid=3400) which means at most you can get is 5-10 more CFM with a typical Carrier 80% furnace blower... so adding another return won't make much of a difference in my opinion.
    You can call me Sam

    It should be a crime to be a mechanical engineer in San Diego
    Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

  6. #19
    Join Date
    Jan 2012
    Location
    indy
    Posts
    471
    Quote Originally Posted by George2 View Post
    Check the airflow with the door to the AH closed and then check it with the door open.

    That is an easy way to determine if the unit is getting enough return air.

    I agree with Genduct that even though the grille is too small, your AH is getting air (maybe enough or not) through the nooks and crannies.

    Try the above and let us know. P.S. How many suppies are in the home?
    I'm not understanding your description. If you take the coil door off of course the static is going to change the fan is bypassing the coil right in through the door, path of least resistance, just ckecking r/a alone and total esp will tell you alot, maybe like I said, not understading you method.

  7. #20
    Join Date
    May 2012
    Location
    San Diego, CA
    Posts
    352
    Quote Originally Posted by tlhiv View Post
    Now don't laugh, but we like to keep it around 70F throughout the day, and on many days our system will "maintain" this temperature but if we decide to let it get to 72F for some reason, then the unit will not typically bring the temperature in the house back down to 70F until the outside temperature has significantly dropped.

    Our house (and unit) is 5 years old. We bought both completely new. We are the only homeowners of this house, and the unit was installed the day before we moved in.
    70 F is okay, I like it 70 F on a hot summer day . Unfortunately your unit is probably sized for a 74-75 F design temperature. House and unit are both fairly new... so it doesn't seem like a leaky house... No leaky supply ducts or long supply duct runs? Do you have flexible supply ducts?

    You should see if your supply are giving you 1200 cfm... if not you might need a bigger blower.
    You can call me Sam

    It should be a crime to be a mechanical engineer in San Diego
    Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

  8. #21
    Join Date
    Jun 2010
    Posts
    16
    Quote Originally Posted by hcong View Post
    70 F is okay, I like it 70 F on a hot summer day . Unfortunately your unit is probably sized for a 74-75 F design temperature. House and unit are both fairly new... so it doesn't seem like a leaky house... No leaky supply ducts or long supply duct runs? Do you have flexible supply ducts?

    You should see if your supply are giving you 1200 cfm... if not you might need a bigger blower.
    When you say it is "sized" for a 74-75 design temperature, do you mean the tonage (3 ton) of the compressor/condensor unit and the (3 ton) evaporator unit?

    I don't know of any leaks as, like you said, it is a new house. To my knowledge there are no leaky ducts. We do not have very long duct runs, and most (perhaps all) of the runs from the trunk to each supply register is flex.

  9. #22
    Join Date
    May 2012
    Location
    San Diego, CA
    Posts
    352
    Quote Originally Posted by tlhiv View Post
    When you say it is "sized" for a 74-75 design temperature, do you mean the tonage (3 ton) of the compressor/condensor unit and the (3 ton) evaporator unit?

    I don't know of any leaks as, like you said, it is a new house. To my knowledge there are no leaky ducts. We do not have very long duct runs, and most (perhaps all) of the runs from the trunk to each supply register is flex.
    Yeah, if you assume everything else is in perfect condition... then your 3 ton might not be able to hold 70 F. Usually when engineers or contractor do the load calculations to choose your condenser and coils, they assume the residents will run the AC to hold at least 74-75 F. The goal these days is to undersize units... I would still maybe sure you are getting the correct amount of air through your supply registers... adding the return grille from my quick calculations won't give you much.

    If you bought one of those houses from a national builder... they will put the same system in all their homes no matter which way the windows face or house is oriented.
    You can call me Sam

    It should be a crime to be a mechanical engineer in San Diego
    Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

  10. #23
    Join Date
    Jun 2010
    Posts
    16
    Quote Originally Posted by hcong View Post
    I would still maybe sure you are getting the correct amount of air through your supply registers... adding the return grille from my quick calculations won't give you much.
    How can I measure this? Do I have to have a special meter to measure the amount of air flow?

  11. #24
    Join Date
    May 2012
    Location
    San Diego, CA
    Posts
    352
    http://www.amazon.com/s/ref=nb_sb_no...ords=CFM+meter

    Might be cheaper to get someone who has the device and just get a full inspections so you know nothing else is wrong.
    You can call me Sam

    It should be a crime to be a mechanical engineer in San Diego
    Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

  12. #25
    Join Date
    Jun 2010
    Posts
    16
    Quote Originally Posted by hcong View Post
    http://www.amazon.com/s/ref=nb_sb_no...ords=CFM+meter

    Might be cheaper to get someone who has the device and just get a full inspections so you know nothing else is wrong.
    Indeed

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