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  1. #1
    Join Date
    Aug 2011
    Location
    North Orange County, CA
    Posts
    5

    HVAC return, size & configuration

    We recently moved into our house and had central HVAC installed to replace the old forced air furnace. Unfortunately, the return is in the living room near the TV, and it's very noisy when the system is running. Some of the noise comes from the furnace being located just behind that wall, but the main problem is the loud sucking noise from the return, and we'd like to reduce it if we can.

    Our house is a single story of appx 1200 sq ft, the furnace is a Rheem RGPN-05NAUER (3-ton), and the return opening measures 8x24" or 192 sq in. There is no actual duct for the return; the furnace sits on a raised, enclosed platform in the closet appx 17" above the floor, and the return opening feeds directly into that open space, which measures 48x50" or 2400 sq in. The system cools well, but the living room and its adjacent room (both up front with no door between) tend to be a little cooler than the rest of the house.

    From what I've read, it looks like the return opening is too small regardless of noise or cooling concerns, and I expect that having it enlarged would help reduce the sucking noise. I'm debating whether to bring the contractor back (he took a couple other shortcuts) or call in someone else, but is there some sort of formula or general rule for sizing the return opening? Alternatively, would a second opening be acceptable or advisable? It would be in an adjacent room up front or in the dining room just beyond (all share walls with that closet).

    Also, I'm curious as to whether the return arrangement with that open space under the furnace is okay, as opposed to having an actual duct from the return opening to the furnace. I don't think it would cost a lot to have one installed but I'd rather not spend the money if it's unnecessary.

    I'm not interested in DIY, I just want to get a handle on things before I proceed. I expect I've already made mistakes by not being better informed.

  2. #2
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    4,663
    Quote Originally Posted by chris-oc View Post
    We recently moved into our house and had central HVAC installed to replace the old forced air furnace. Unfortunately, the return is in the living room near the TV, and it's very noisy when the system is running. Some of the noise comes from the furnace being located just behind that wall, but the main problem is the loud sucking noise from the return, and we'd like to reduce it if we can.

    Our house is a single story of appx 1200 sq ft, the furnace is a Rheem RGPN-05NAUER (3-ton), and the return opening measures 8x24" or 192 sq in. There is no actual duct for the return; the furnace sits on a raised, enclosed platform in the closet appx 17" above the floor, and the return opening feeds directly into that open space, which measures 48x50" or 2400 sq in. The system cools well, but the living room and its adjacent room (both up front with no door between) tend to be a little cooler than the rest of the house.

    From what I've read, it looks like the return opening is too small regardless of noise or cooling concerns, and I expect that having it enlarged would help reduce the sucking noise. I'm debating whether to bring the contractor back (he took a couple other shortcuts) or call in someone else, but is there some sort of formula or general rule for sizing the return opening? Alternatively, would a second opening be acceptable or advisable? It would be in an adjacent room up front or in the dining room just beyond (all share walls with that closet).

    Also, I'm curious as to whether the return arrangement with that open space under the furnace is okay, as opposed to having an actual duct from the return opening to the furnace. I don't think it would cost a lot to have one installed but I'd rather not spend the money if it's unnecessary.

    I'm not interested in DIY, I just want to get a handle on things before I proceed. I expect I've already made mistakes by not being better informed.
    Noise/sucking/vibration, to me, means add an extra return.

    The cost of installing one of these returns is going to depend on alot of factors. If it's easy to install, you'll love the price. If it's tough to do, you probably won't want it done.
    Can't get into pricing.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  3. #3
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,635
    3 ton needs 1200 cfm airflow, on 1200 square feet? That's like putting a 1200 horsepower engine in a hundai. You can now change the transmission (duct) but that will simply shift the problem to brakes and suspension.

    Was an audit or load calc done? Sounds grossly oversized. Counter to common thought, bigger is NOT better when it comes to hvac. Unfortunate for you to learn this first hand.

    1.5 ton will cut airflow requirements in half, likely bringing all other issues into balance. Good luck.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  4. #4
    Join Date
    Oct 2010
    Location
    SW Michigan, near Battle Creek
    Posts
    921
    but enlarging the return and/or lowering the airflow to the minimum the system needs might realy reduce the noise. turning the t-stat fan switch to "on" will make the noise more constant (no fan on fan off) and might realy improve temp spread.

  5. #5
    Join Date
    Aug 2011
    Location
    North Orange County, CA
    Posts
    5
    Quote Originally Posted by tedkidd View Post
    3 ton needs 1200 cfm airflow, on 1200 square feet? That's like putting a 1200 horsepower engine in a hundai.
    That's one of the things I learned too late. We got bids from three different contractors and all had the same recommondation regarding size, so I didn't question it further. I wish I had known better, but what's done is done unless we want to spend another few thousand.

    For now I'll be happy just to have the existing system work better, and I appreciate the suggestions. Now I know that I'll be calling another contractor to help.

  6. #6
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,635
    All might not be lost, but you will need to slow down and not rush to solving. Often we see homeowners run around senselessly, bleeding like a chicken with it's head cut off.

    If you bought from a reputable company they may be convinced to replace with a smaller unit. Even Joe one man band, if he has any ethics, should be willing to correct such a mistake.

    Can you put your zip in your username, it's helpful to see that.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  7. #7
    Join Date
    Aug 2011
    Location
    North Orange County, CA
    Posts
    5
    Trust me, I'm not rushing into anything; right now I'm focused on my HVAC education. I expect it's worth discussing with the installation contractor, but he was quite insistent about the tonnage, with an explanation that made sense at the time. As I noted, he also took a few other shortcuts I was not thrilled with, including the air return issue. One other matter has been fixed, but it took a while.

    I've added my location above.

  8. #8
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,635
    Quote Originally Posted by chris-oc View Post
    Trust me, I'm not rushing into anything; right now I'm focused on my HVAC education. I expect it's worth discussing with the installation contractor, but he was insistent on the tonnage, explaining that a larger unit doesn't need to run as long as a smaller one for the same effect and therefore is not overworked, lasts longer, etc.

    I've added my location above.
    If it weren't causing you pain, that explanation would be really funny.

    Equipment likes to run. It's the off and on that's hard on it. IMO, His insistence is his downfall, he had you count on him and he was wrong. Had you insisted it would be on you.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  9. #9
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,474

    Lightbulb

    If the system were to have a TXV, after U get the Return Air retrofit done, U can slow the blower down to perhaps a minimum of say 325 per/ton (or 975-cfm) of cooling.

    A TXV will throttle down the flow of liquid refrigerant to maintain, say a 12-F Superheat, thus reducing BTUH capacity, generating longer runtime cycles.

    If U add a temperature differential room thermostat with half degree increments up to a 3-F maximum, the 3-ton might get by.

    Especially if U live in a high humidity climate the colder evap coil coupled with decently long runtime cycles might provide decent comfort levels; say it's set to kick on at 78-F & off at 75-F, that should provide sufficient runtime U can always use a lesser temp spread....

  10. #10
    Join Date
    Aug 2011
    Location
    North Orange County, CA
    Posts
    5
    Quote Originally Posted by udarrell View Post
    If the system were to have a TXV, after U get the Return Air retrofit done, U can slow the blower down to perhaps a minimum of say 325 per/ton (or 975-cfm) of cooling. A TXV will throttle down the flow of liquid refrigerant to maintain, say a 12-F Superheat, thus reducing BTUH capacity, generating longer runtime cycles.
    I just read a little more about a TXV and I like the idea, regardless of any problems that might exist otherwise. Can this be added to an existing system?

    If U add a temperature differential room thermostat with half degree increments up to a 3-F maximum, the 3-ton might get by.
    The thermostat is a Honeywell TH6110D; I don't know if it's the type you referred to.

  11. #11
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,474
    Quote Originally Posted by chris-oc View Post
    I just read a little more about a TXV and I like the idea, regardless of any problems that might exist otherwise. Can this be added to an existing system?

    A TXV can be installed.
    Are U sure it doesn't have one?


    The thermostat is a Honeywell TH6110D; I don't know if it's the type you referred to.
    I don't think it has any temp differential settings, or a way to set cycles per hour.
    Someone may be more familiar with it.
    ----------------
    http://www.google.com/url?sa=t&sourc...pSSBDf1ypJB5xw
    The Robertshaw 9400 is a single-stage thermostat designed to control ... Adjustable temperature differential: .5F to 3.0F (0.5C to 1.5C) ....
    Half degree increments. Link may not load; do a search...

    Low priced.
    Last edited by udarrell; 08-28-2011 at 04:47 PM. Reason: Link may not load, do a search...

  12. #12
    Join Date
    Aug 2011
    Location
    North Orange County, CA
    Posts
    5
    I don't know if the system has a TXV. Is this something I can see easily?

  13. #13
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,474
    Been off line till now, finally checked my e-mail...

    Usually they are mounted inside the plenum; all depends on the setup.
    Get someone to check it for you.

    http://www.central-air-conditioner-a...ion_valve.html

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