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  1. #1

    Need 2nd opinion: Getting Conflicting Proposals on 4 vs 5 ton for new HVAC system

    This is my first post. Judging from the quality of the discussion here, I'm hoping to get some guidance to help me make decision between several quotes to replace my current system. We have a cracked heat exchanger which is still under parts warranty but it's $ repair on 12 year old system so we're looking to replace entire system. Home is 12 years old so no one is recommending duct work aside from modifications to increase return air (details below). Sorry for the long post but I am learning how complex HVAC can be so hope these details help you in your responses.

    My Dilemma
    I've narrowed it down to 4 quotes from 3 reputable firms. I understand that installation is crucial factor and have researched BBB and Angieslist and all three companies have solid reputations. The quotes are also for well regarded manufacturers (Lennox, Ruud, Rheem). Cost wise two bids are very close and the 3rd company is a bit cheaper but my first priority is properly designed/installed system.

    My biggest concern is that the proposals seem to be spec'ing out fundamentally different designs. Below are specific points of differences I'm seeing in the bids
    1) AC (4 ton, single stage vs 5 dual stage)
    2) Extent of changes to return air
    3) Replacement vs reuse of line set


    About our current system
    * 12 years old (original unit built with home)
    * Goodman, 5 ton, builder grade, 10 SEER external condenser, 80% AFUE horizontal gas furnace in attic, all single stage
    * Single 20x30 return grill using 1" 3M Ultra Allergen filters
    * Doing adequate job of meeting our current cooling target of 79-80F; however, sometimes it seems a little slow to kick on (temperature swings)

    About the Home
    * 2 story, 2588 sq.ft
    * 4 bedrooms, 2.5 bath, 4 living spaces (family room, dining room, living room, loft) plus kitchen with nook
    * 2 zones (up/down)
    * Near Sacramento California (>100F most of the summer with peaks regularly over 105F, going up to 110 in some years).

    Useful Data Points
    * Two heat load calcs were performed (one was 45k and other was 48,512 BTU's). Note: The guy who calc'd 48,512 figure assumed 8 people; whereas 45k figure assumed 5 people (but that only accounts for about half of the discrepancy)
    * One guy measured airflow at the return grill with both zones on simultaneously and got 3.25 tons of flow
    * Static pressure appears pretty high based on filter caving in when system was running.

    The Bids
    All the bids have similar furnaces (80% AFUE, dual stage, variable speed) and warranties. Below are more specifics of the 4 bids

    Bid #1: Lennox 4 ton (single stage cool, dual stage heat) 15SEER/12.5EER* Condenser: XC14-048-230
    * Furnace: SL280UH090V60C
    * Airflow: No changes (bid includes Healthy Climate 10 air filter which eliminates 1" filters at return grill)
    * New external line set (company policy to NOT reuse line sets)
    * Re-use current zone control

    Bid#2: Ruud 4 ton (single stage cool, dual stage heat) 16SEER/13EER* Condenser: 14AJM49 Value Series
    * Furnace: RGPE10NBRMR Ultra Series
    * Airflow: New return air (high velocity grill, bigger return can and box at furnace intake) ==> Guarantees airflow will achieve at least 95% of 4 ton capability
    * Re-use line set
    * New zone control board, electronic dampers and barometric relief

    Bid#3A: Rheem 5 ton (dual stage cool, dual stage heat) 16SEER/13EER* Condenser: RARL060JE2
    * Furnace: RGPE10NBRMR
    * Airflow: Changes to return air to support 5 ton flow (high velocity grill, ducting)
    * Re-use line set
    * New zone control board

    Bid #3B: Rheem 4 ton (single stage cool, dual stage heat) 16SEER/13SEER
    Note: Same company as #3A just different eqpt
    * Condenser: 14AJM49A01
    * Furnace: RGPE10NBRQR
    * Airflow: Changes to return air to support 5 ton flow (high velocity grill, ducting)
    * Re-use line set
    * New zone control board

    My Questions
    Would appreciate expert opinion on the pros/cons of these different proposals and the things I should be thinking about. Any other comments that may influence my decision (brand, quality etc) is also appreciated.

    My specific questions are:
    1) Is 5 ton overkill for my situation and does the fact its 2 stage matter? 2 of 3 companies advised against it (bids 1 & 2) but bid#3 was insistent that I needed 5 ton for those hottest days in the summer (they gave me the 4 ton quote at my insistence).
    2) Is the assumption of 8 people in the 48,512 heat load calc too high? Others have told me that 5 (size of my family) or 6 (1 person per bedroom + 2 in master). Even if 48,512 is valid, being it is just over the 48,000 cut off so does that really warrant a 5 ton system?
    3) We really like the idea of 2 stage cooling but only found it in the 5 ton proposal. If we went this route, should I be concerned about short cycling? Does the fact it's 2 stage mitigate these concerns at all?
    4) Is my current 20x30 return adequate for 4 ton? Bid #2 told me builders woefully undersize returns and that there no way my 20x30 would ever support a 5 ton system (unless I add another return) which is why they spec'd 4 ton. Bid #1 told me that nothing other than eliminating the return grill filter with Healthy Climate furnace mount filter was needed for 4 ton.
    5) Is my current 20x30 return adequate for 5 ton? Bid #3 says that with some duct/grill changes 20x30 will be fine to support 5 ton. If I went this route, would I end up with air velocity/noise problems?
    6) Is there any concerns about re-using line set rather than new line set? I've been told that dual stage compressors are more sensitive to residual refrigerant not being fully purged. Is this true?
    7) Are there any concerns or special requirements using a 2 stage compressor with zoned system?
    7) How can I find out cooling capacity of the 2 stage 5 ton Rheem AC I'm considering under #3A when it's running the 1st stage only?

    Sorry again for the long post and the tons of question. Any help, info or guidance is much appreciated.
    Last edited by beenthere; 07-29-2012 at 06:45 AM. Reason: price

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Hmm VARIOUS CONDITIONS MUST BE STUDIED

    Quote Originally Posted by MS64MEE View Post
    This is my first post. Judging from the quality of the discussion here, I'm hoping to get some guidance to help me make decision between several quotes to replace my current system.


    My Dilemma

    I've narrowed it down to 4 quotes from 3 reputable firms. I understand that installation is crucial factor and have researched BBB and Angieslist and all three companies have solid reputations. The quotes are also for well regarded manufacturers (Lennox, Ruud, Rheem). Cost wise two bids are very close and the 3rd company is a bit cheaper but my first priority is properly designed/installed system.

    My biggest concern is that the proposals seem to be spec'ing out fundamentally different designs. Below are specific points of differences I'm seeing in the bids
    1) AC (4 ton, single stage vs 5 dual stage)
    2) Extent of changes to return air
    3) Replacement vs reuse of line set

    About our current system
    * 12 years old (original unit built with home)
    * Goodman, 5 ton, builder grade, 10 SEER external condenser, 80% AFUE horizontal gas furnace in attic, all single stage

    * Single 20x30 return grill using 1" 3M Ultra Allergen filters

    * Doing adequate job of meeting our current cooling target of 79-80F; however, sometimes it seems a little slow to kick on (temperature swings)

    About the Home
    * 2 story, 2588 sq.ft
    * 4 bedrooms, 2.5 bath, 4 living spaces (family room, dining room, living room, loft) plus kitchen with nook
    * 2 zones (up/down)
    * Near Sacramento California (>100F most of the summer with peaks regularly over 105F, going up to 110 in some years).


    Useful Data Points
    * Two heat load calcs were performed (one was 45k and other was 48,512 BTU's).

    * Static pressure appears pretty high based on filter caving in when system was running.

    The Bids
    All the bids have similar furnaces (80% AFUE, dual stage, variable speed) and warranties. Below are more specifics of the 4 bids

    Bid #1: Lennox 4 ton (single stage cool, dual stage heat) 15SEER/12.5EER* Condenser: XC14-048-230
    * Furnace: SL280UH090V60C
    * Airflow: No changes (bid includes Healthy Climate 10 air filter which eliminates 1" filters at return grill)
    * New external line set (company policy to NOT reuse line sets)
    * Re-use current zone control

    Bid#3A: Rheem 5 ton (dual stage cool, dual stage heat) 16SEER/13EER* Condenser: RARL060JE2
    * Furnace: RGPE10NBRMR
    * Airflow: Changes to return air to support 5 ton flow (high velocity grill, ducting)
    * Re-use line set
    * New zone control board

    Any other comments that may influence my decision (brand, quality etc) is also appreciated.

    My specific questions are:

    1) Is 5 ton overkill for my situation and does the fact its 2 stage matter?

    2 of 3 companies advised against it (bids 1 & 2) but bid#3 was insistent that I needed 5 ton for those hottest days in the summer (they gave me the 4 ton quote at my insistence).

    3) We really like the idea of 2 stage cooling but only found it in the 5 ton proposal. If we went this route, should I be concerned about short cycling? Does the fact it's 2 stage mitigate these concerns at all?

    4) Is my current 20x30 return adequate for 4 ton?

    Bid #2 told me builders woefully undersize returns and that there no way my 20x30 would ever support a 5 ton system (unless I add another return) which is why they spec'd 4 ton.

    Bid #1 told me that nothing other than eliminating the return grill filter with Healthy Climate furnace mount filter was needed for 4 ton.

    5) Is my current 20x30 return adequate for 5 ton? Bid #3 says that with some duct/grill changes 20x30 will be fine to support 5 ton. If I went this route, would I end up with air velocity/noise problems?

    6) Is there any concerns about re-using line set rather than new line set? I've been told that dual stage compressors are more sensitive to residual refrigerant not being fully purged. Is this true?

    7) Are there any concerns or special requirements using a 2 stage compressor with zoned system?

    8) How can I find out cooling capacity of the 2 stage 5 ton Rheem AC I'm considering under #3A when it's running the 1st stage only?
    http://www.wunderground.com/history/...q_statename=NA

    The FIRST fix would be to GET RID of the 3M filters which are V E R Y Restrictive and degrade performance.

    8) First stage of about 0.7 * 60,000 = 42,000 Total.
    SENSIBLE cooling capacity is about 34,000 BTU/Hr.

    4) 20 x 30 = 600 sq inch = ~ 4 sq feet = ~ 1,200 CFM
    which is generally adequate for a 3-ton.
    With a 3M 1" filter, 20x30 filter is not adequate for 3-ton.

    I would not select RUUD nor RHEEM.

    Basis (inside and outdoor temperatures) for calculated cooling load requirements are not provided.

    It is difficult to judge the MAXIMUM Hourly load not having the load calculation and without an analysis for slightly increased upper level temperature.

    5-ton unit will provide about 47,000 BTU Hr SENSIBLE Capacity.
    4-ton _____"__________"__ 38,000 ___________" ________________

    How many windows/ sliding glass doors and orientation?
    340 total square feet [ 18 ] is a general average for 2,500 sq. foot
    120 square feet of WEST facing windows [ 5 or 6 ] may be a load of close to 1-ton. I would have West facing windows tinted to SHGC of < 0.4 if they are not already in order to minimize load so a 4-ton would be adequate.

    Are you willing to have 82'F upstairs in mid afternoon when
    outdoor temp > 95'F so the lower level is provided full air flow most of the time? If yes, a four ton unit may be adequate.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #3
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,296
    4 tons is plenty if airflow is addressed. Keep in mind with 3.25tons of current airflow you aren't actually GETTING the 5 tons out of the current system. If 4 tons is too small the worst that will happen is the upstairs will be a bit warm from about 2-7pm on the days that it's really hot. If upstairs is primarily a sleeping area it should be cooled off by 9 or so.

    I'm not so sure that the supply ductwork will will support TEN TONS of cooling. EACH zone should be able to support the entire capacity of the system. If only one zone is calling ALL of the air goes through that zones ductwork. Chances are current ductwork won't support 8 tons, much less 10. Was the 3.25ton test done with a 3M filter?

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #5
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,698
    First, and most important, is that your existing system is not performing to it's ability because it's so short on the return side.

    I'm sure, in your mind, you "think" you need a 5 ton because that's what came with the house.

    You mentioned a zone board. Do you have thermostats on both levels?

    If so, and the load calc. is correct, a 4 ton 2-speed would be a sweet A/C (or H/P).

    The return MUST be modified. Reusing the refrigerant lines, if they are clean, the proper size and there are no kinks or joints, is okay.

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,189
    8 people seems a bit high. If you have 6 people, I'd probably use that.

    If you have zoning, 2 stage heat & cool would be nice. I would insist on a good zone panel that has capacity control, meaning not letting the equipment go to high unless both zones were asking for air. That reduces short cycling do to over capacity of heat or cool. The 2 stage scroll almost everyone uses these days run fairly high on low stage. On the RARL-061, low is 85% of high which is the highest I've seen. Pretty rare to see low at 70% of high.

    Now, I will definitely disagree with Dan on avoiding Rheem/Ruud. We've sold it for 25 years with excellent results. Like everyone, they've had some issues over the years and like everyone, things now are made pretty cheaply but it is good, solid equipment. I'd put the RGPE and RARL against anything out there. In 20 years that the 34" furnaces have been on the market, we have not found 1 bad heat exchanger. Not 1. Only brand close to that record in our experience is A-S/Trane. The 14AJM is a no extras builder model, a bit noisy. The RAPM is so much nicer but more money.

  7. #7
    Thanks for all the detailed responses. Very helpful indeed. I'll try to respond to your specific questions/comments below but first one add'l question about the heat load calculation.

    When I went back over the paperwork that bid#3 left me (48512). I noticed he input 2,588 as the ceiling square footage. From what little I've been able to learn it seems the ceiling calculation is related to heat transfer with attic. Since my house is 2 story, the ceiling connected to attic is roughly half of my total square footage. Interestingly, after correcting for this and the # of people, I get awfully close to the 45k that the other bids calculated.

    Quote Originally Posted by 54regcab View Post
    4 tons is plenty if airflow is addressed. Keep in mind with 3.25tons of current airflow you aren't actually GETTING the 5 tons out of the current system. If 4 tons is too small the worst that will happen is the upstairs will be a bit warm from about 2-7pm on the days that it's really hot. If upstairs is primarily a sleeping area it should be cooled off by 9 or so.
    This was exactly the point that one of my contractors raised too. He said that after correcting for airflow, I'll get more cooling capacity out of his 4 ton system.

    Quote Originally Posted by 54regcab View Post
    I'm not so sure that the supply ductwork will will support TEN TONS of cooling. EACH zone should be able to support the entire capacity of the system. If only one zone is calling ALL of the air goes through that zones ductwork. Chances are current ductwork won't support 8 tons, much less 10.
    FWIW None of the guys recommended any changes on the supply side. As part of their walk through they did take notes of the size, location and qty of all the supply vents. In response to my complaint about some temp unevenness (north side upstairs master at end of house tends to be 2-3 degrees colder than thermostat), they felt that could be addressed with damper adjustments.

    Quote Originally Posted by 54regcab View Post
    Was the 3.25ton test done with a 3M filter?
    Yes. How much would that affect the airflow measurements? I change these per 3M guidelines (every 3 months).


    Quote Originally Posted by George2 View Post
    I'm sure, in your mind, you "think" you need a 5 ton because that's what came with the house.).
    Actually, I was leaning toward the 4 ton based on the majority of the bids I got, the heat load calcs and airflow constraints. However, I am leaning toward the contractor that gave me the 5 ton bid (but take their 4 ton option). However, if the fact they recommended a 5 ton at all is grounds to question their technical competence, I'd like to know that.

    Quote Originally Posted by George2 View Post
    You mentioned a zone board. Do you have thermostats on both levels
    Yes.

    Quote Originally Posted by George2 View Post
    If so, and the load calc. is correct, a 4 ton 2-speed would be a sweet A/C (or H/P).
    I did like the 2 speed aspect of the 5 ton quote. For some reason, none of my 4 ton quotes offered 2 speed. I'll ask what options they have 4 ton 2 speed.

    Quote Originally Posted by BaldLoonie View Post
    If you have zoning, 2 stage heat & cool would be nice. I would insist on a good zone panel that has capacity control, meaning not letting the equipment go to high unless both zones were asking for air. That reduces short cycling do to over capacity of heat or cool. The 2 stage scroll almost everyone uses these days run fairly high on low stage. On the RARL-061, low is 85% of high which is the highest I've seen. Pretty rare to see low at 70% of high.
    Thanks. I'll ask if the zone control board they have in mind has this capability. Would you still recommend this feature if I go with the 4 ton or was your advice geared toward the 5 ton option?

  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Exclamation

    Quote Originally Posted by MS64MEE View Post
    Thanks for all the detailed responses. Very helpful indeed. I'll try to respond to your specific questions/comments below but first one add'l question about the heat load calculation.

    This was exactly the point that one of my contractors raised too. He said that after correcting for airflow, I'll get more cooling capacity out of his 4 ton system.

    Yes. How much would that affect the airflow measurements? I change these per 3M guidelines (every 3 months).
    I would expect 20% to 50% reduction in flow depending on the filter and the blower performance.

    A NEW 3M filter is TtTTTTTTTTTOOOOOOOOOOOO Restrictive.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  9. #9
    Join Date
    Mar 2007
    Location
    Myrtle Beach, SC
    Posts
    2,919
    Quote Originally Posted by MS64MEE View Post
    This is my first post. Judging from the quality of the discussion here, I'm hoping to get some guidance to help me make decision between several quotes to replace my current system. We have a cracked heat exchanger which is still under parts warranty but it's $ repair on 12 year old system so we're looking to replace entire system. Home is 12 years old so no one is recommending duct work aside from modifications to increase return air (details below). Sorry for the long post but I am learning how complex HVAC can be so hope these details help you in your responses.

    My Dilemma
    I've narrowed it down to 4 quotes from 3 reputable firms. I understand that installation is crucial factor and have researched BBB and Angieslist and all three companies have solid reputations. The quotes are also for well regarded manufacturers (Lennox, Ruud, Rheem). Cost wise two bids are very close and the 3rd company is a bit cheaper but my first priority is properly designed/installed system.

    My biggest concern is that the proposals seem to be spec'ing out fundamentally different designs. Below are specific points of differences I'm seeing in the bids
    1) AC (4 ton, single stage vs 5 dual stage)
    2) Extent of changes to return air
    3) Replacement vs reuse of line set


    About our current system
    * 12 years old (original unit built with home)
    * Goodman, 5 ton, builder grade, 10 SEER external condenser, 80% AFUE horizontal gas furnace in attic, all single stage
    * Single 20x30 return grill using 1" 3M Ultra Allergen filters
    * Doing adequate job of meeting our current cooling target of 79-80F; however, sometimes it seems a little slow to kick on (temperature swings)

    About the Home
    * 2 story, 2588 sq.ft
    * 4 bedrooms, 2.5 bath, 4 living spaces (family room, dining room, living room, loft) plus kitchen with nook
    * 2 zones (up/down)
    * Near Sacramento California (>100F most of the summer with peaks regularly over 105F, going up to 110 in some years).

    Useful Data Points
    * Two heat load calcs were performed (one was 45k and other was 48,512 BTU's). Note: The guy who calc'd 48,512 figure assumed 8 people; whereas 45k figure assumed 5 people (but that only accounts for about half of the discrepancy)
    * One guy measured airflow at the return grill with both zones on simultaneously and got 3.25 tons of flow
    * Static pressure appears pretty high based on filter caving in when system was running.

    The Bids
    All the bids have similar furnaces (80% AFUE, dual stage, variable speed) and warranties. Below are more specifics of the 4 bids

    Bid #1: Lennox 4 ton (single stage cool, dual stage heat) 15SEER/12.5EER* Condenser: XC14-048-230
    * Furnace: SL280UH090V60C
    * Airflow: No changes (bid includes Healthy Climate 10 air filter which eliminates 1" filters at return grill)
    * New external line set (company policy to NOT reuse line sets)
    * Re-use current zone control

    Bid#2: Ruud 4 ton (single stage cool, dual stage heat) 16SEER/13EER* Condenser: 14AJM49 Value Series
    * Furnace: RGPE10NBRMR Ultra Series
    * Airflow: New return air (high velocity grill, bigger return can and box at furnace intake) ==> Guarantees airflow will achieve at least 95% of 4 ton capability
    * Re-use line set
    * New zone control board, electronic dampers and barometric relief

    Bid#3A: Rheem 5 ton (dual stage cool, dual stage heat) 16SEER/13EER* Condenser: RARL060JE2
    * Furnace: RGPE10NBRMR
    * Airflow: Changes to return air to support 5 ton flow (high velocity grill, ducting)
    * Re-use line set
    * New zone control board

    Bid #3B: Rheem 4 ton (single stage cool, dual stage heat) 16SEER/13SEER
    Note: Same company as #3A just different eqpt
    * Condenser: 14AJM49A01
    * Furnace: RGPE10NBRQR
    * Airflow: Changes to return air to support 5 ton flow (high velocity grill, ducting)
    * Re-use line set
    * New zone control board

    My Questions
    Would appreciate expert opinion on the pros/cons of these different proposals and the things I should be thinking about. Any other comments that may influence my decision (brand, quality etc) is also appreciated.

    My specific questions are:
    1) Is 5 ton overkill for my situation and does the fact its 2 stage matter? 5 ton sounds large but the load calculation decides that. I can't tell from here. Normally allow 2 people for the master bedroom + one more for every other bedroom. A 2 stage ac overcomes some but not all problems with over sizing. 2 of 3 companies advised against it (bids 1 & 2) but bid#3 was insistent that I needed 5 ton for those hottest days in the summer (they gave me the 4 ton quote at my insistence).
    2) Is the assumption of 8 people in the 48,512 heat load calc too high? Others have told me that 5 (size of my family) or 6 (1 person per bedroom + 2 in master). Even if 48,512 is valid, being it is just over the 48,000 cut off so does that really warrant a 5 ton system?
    3) We really like the idea of 2 stage cooling but only found it in the 5 ton proposal. If we went this route, should I be concerned about short cycling? Does the fact it's 2 stage mitigate these concerns at all? 2 stage 5 ton cooling will have about 3.5 tons on low stage. So that helps with short cycling.
    4) Is my current 20x30 return adequate for 4 ton? NO. Marginal on 3 ton with cheap filter. Too small on 3 ton with pleated filter. Stay away from 3M filters unless you more than DOUBLE the area of your filter grille. Adding a second 20 x 30 filter grille would be a good start. Bid #2 told me builders woefully undersize returns and that there no way my 20x30 would ever support a 5 ton system (unless I add another return) which is why they spec'd 4 ton. Bid #1 told me that nothing other than eliminating the return grill filter with Healthy Climate furnace mount filter was needed for 4 ton. Healthy Climate has high resistance too, but not as bad as that 1" 3M compressor killer.
    5) Is my current 20x30 return adequate for 5 ton? NOOOOOOOO!!!! Bid #3 says that with some duct/grill changes 20x30 will be fine to support 5 ton. If I went this route, would I end up with air velocity/noise problems? Yes, very likely noisy, if you got enough air flow.
    6) Is there any concerns about re-using line set rather than new line set? I've been told that dual stage compressors are more sensitive to residual refrigerant not being fully purged. Is this true? Never heard of that one. Sizing is important for oil return in heat pumps, but your evaporator is above your condenser, so that should not be an issue. Flush the lines and you should be ok if they are big enough. Even flushing may not be necessary. It seems the old mineral oil and the new POE oil get along better than they first thought.
    7) Are there any concerns or special requirements using a 2 stage compressor with zoned system? Air flow should be adjusted to match capacity of both stages. A VS Blower should do that nicely.
    7) How can I find out cooling capacity of the 2 stage 5 ton Rheem AC I'm considering under #3A when it's running the 1st stage only? Lennox is usually 65% of high stage capacity.

    Sorry again for the long post and the tons of question. Any help, info or guidance is much appreciated.
    See answers posted in-line in RED.
    Remember, Air Conditioning begins with AIR.

  10. #10
    Join Date
    Apr 2012
    Location
    Paper Street Soap Company
    Posts
    2,304
    There is no good reason from a operation stand point to replace a line set when converting from 410 to 22.

    To hear that its a contractors policy ? Strange.

    Rheem Ruud and Lennox wouldn't be in my top 3 choices.

    American Standard makes execellent equipment and then its Carrier.

  11. #11
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295
    2588 A
    0.033333333 U
    130 T attic
    76 T room
    54 dT
    4658.4 Q = U * A * dT

    Subract 2,329 BTU/ hr from the calculated ~ 45,000
    to account for only 2,558/2 ceiling area.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  12. #12
    Thanks again guys for additional responses. Just realized I missed replying to some of designer Dan's questions so here they are:

    Quote Originally Posted by dan sw fl View Post
    Basis (inside and outdoor temperatures) for calculated cooling load requirements are not provided.
    The paperwork they left me says they were designing to 95F day but it doesn't say the target inside temp. My memory is fuzzy but I seem to recall 75F. Sorry, I'll ask next time I talk to the contractor.

    Quote Originally Posted by dan sw fl View Post
    It is difficult to judge the MAXIMUM Hourly load not having the load calculation and without an analysis for slightly increased upper level temperature.
    Sorry don't follow your question.

    Quote Originally Posted by dan sw fl View Post
    How many windows/ sliding glass doors and orientation?
    340 total square feet [ 18 ] is a general average for 2,500 sq. foot
    120 square feet of WEST facing windows [ 5 or 6 ] may be a load of close to 1-ton. I would have West facing windows tinted to SHGC of < 0.4 if they are not already in order to minimize load so a 4-ton would be adequate.
    We have lots of windows but mostly on E, N & S sides. Total around 457 sqft.
    W: 61 sqft (one 5'x5' downstairs, two 4'x4' upstairs, two 2'x2' upstairs)
    N: 180.5 sqft
    E: 114 sqft
    S: 101.5 sqft

    Quote Originally Posted by dan sw fl View Post
    Are you willing to have 82'F upstairs in mid afternoon when outdoor temp > 95'F so the lower level is provided full air flow most of the time? If yes, a four ton unit may be adequate.
    82F in mid afternoon is bit on high side of comfortable. I work from an upstairs home office (SW corner to boot) alot of the time so it gets toasty already due to me and the PC eqpt. The contractors felt they could solve this problem with increased airflow to that room only.

    Sounds like you're suggesting 4 ton would be marginal to keep up and downstairs at target current target of 79-80F?

    Quote Originally Posted by dan sw fl View Post
    2588 A
    0.033333333 U
    130 T attic
    76 T room
    54 dT
    4658.4 Q = U * A * dT

    Subract 2,329 BTU/ hr from the calculated ~ 45,000
    to account for only 2,558/2 ceiling area.
    Thanks for confirming my thinking on this. However, I would need to subtract this from the 48.5k load calc since he's the one that used 2,588 for the ceiling area. So if I correct his numbers for the ceiling (2588/2 instead of 2588) and the people (6 instead of 8), then I'm looking at:
    48,512 (original load)
    - 2,329 (halve the ceiling area)
    - 1,060 (remove 2 people)
    =====
    45,123

    Which interestingly is the same figure the Lennox contractor came up with. This makes me feel better (understanding why the two are different) and based on your feedback, sounds likes 45k is the correct figure to use.

    Based on this, do you think the 4 ton will struggle to meet my target of 79-80F upstairs on the hottest days?

  13. #13
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,296
    You have stated that your current system gets the job done even with 1300CFM of airflow on a 5 ton unit. Actual output is significantly less than 5 tons due to restricted airflow, I don't see how your current system is getting any more than 4 tons delivered.. When the airflow is upped to 1600CFM the 4 ton condenser will be able to actually deliver the 4 tons of cooling.

    Also keep in mind that the downstairs won't call for cooling very often if the upstairs is already cool. Most of the A/C will be directed to the upstairs. If the upstairs ductwork can handle the full 1600CFM, all the better.

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