Page 1 of 2 12 LastLast
Results 1 to 13 of 18
  1. #1
    Join Date
    Jul 2013
    Posts
    21

    3Ton vs 4Ton and other questions

    My Heatpump died this week. 11 Years old. And I'm getting a few quotes.
    1)Some of the rooms in the upstairs (AH is in basement - 2 floors below) get little or no air from the registers. I have asked the contractors to let me know if I can upgrade from the current 3 ton and if it would make a difference. A couple of the contractors measured the ducts and recon I can go to 4 ton and that I would get more air movement.
    House is 2600sq with another 1200sq for finished basement if it matters
    Would it make a difference? Price seems to be about $ more.
    Some of the contractors checked the returns and registers and no problem there (i.e. its not a problem with return air).

    2)Next I'm seeing a 20%-30% premium for Carrier over Trane (in part I think the guys that install Carrier seems to be bigger operations and thus cost more). In short I realize the price differential is probably not just equipment cost. But I still would like to know if Carrier is worth the premium ITO life expectancy and cost of ownership over the life.

    3)I'm getting some discrepancy on heatpack. Some quote 10kw, most 15kw and others quote 20kw. How do I figure out which it is? And should I run away from quotes that got it wrong?

    4)SEER 13/14 vs 15: Costs savings over an assumed 10yr life would not pay for the price differential. Is it worth it?

    5)Last question that I'm just not understanding from the contractors: 2 stage compressor vs 1 stage (current unit is 1 stage with variable fan on the AH). Again - is it worth it?

    Thanks!
    Last edited by beenthere; 07-14-2013 at 01:15 PM. Reason: Price difference

  2. #2
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,701
    What concerns me is that you're not getting airflow to the second floor now. There is a reason and it's not the equipment. Going with a 4 ton on ductwork that can't handle (maybe) 3 ton won't be good.

    Before I can answer the other questions, I need to know the ductwork size (riser) to the second floor. I should ask, before I assume, where are the registers in the home (on all the levels)? Where, and what size, are the returns?

  3. #3
    Join Date
    Jan 2008
    Posts
    2,031
    Chances are, 4 tons will make your problem worse.
    "Hey Lama, hey, how about a little something, you know, for the effort." And he says, "there won't be any money, but when you die, on your deathbed, you will receive total consciousness." So I got that goin' for me, which is nice. - Carl Spackler

  4. #4
    Join Date
    Jul 2013
    Posts
    21
    Quote Originally Posted by George2 View Post
    What concerns me is that you're not getting airflow to the second floor now. There is a reason and it's not the equipment. Going with a 4 ton on ductwork that can't handle (maybe) 3 ton won't be good.

    Before I can answer the other questions, I need to know the ductwork size (riser) to the second floor. I should ask, before I assume, where are the registers in the home (on all the levels)? Where, and what size, are the returns?
    I'll try and answer - pardon if I do not have the lingo down:
    From the AH there are 2 main supply lines going out in separate directions (length of the house). The one measures 20x8 and the other 16x8. This is the TOTAL of supply for all registers. I cannot tell (due to 95%+ finished basement) where the riser(s) are to the second floor. I have seen a few of the ducts go through the first floor wall to the second floor when doing work on the house. Its regular 6"duct flattened to fit the 3.5" cavity. So my assumption is that the second floor registers uses individual ducts from the 2 main supply lines. But I could be wrong.

    Registers (evenly spaced and most in the floors and the rest low on the walls (in bathrooms)): Basement 7, 1st floor 9, 2nd floor 8 (all 4x10 or 6x10)
    Returns: Basement - a 8" and 6" round, 1st floor 9x8", 2nd floor 13x8 ( I can easily widen the 1st floor one to 13x8")

  5. #5
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,701
    Quote Originally Posted by fstr View Post
    I'll try and answer - pardon if I do not have the lingo down:
    From the AH there are 2 main supply lines going out in separate directions (length of the house). The one measures 20x8 and the other 16x8. This is the TOTAL of supply for all registers. I cannot tell (due to 95%+ finished basement) where the riser(s) are to the second floor. I have seen a few of the ducts go through the first floor wall to the second floor when doing work on the house. Its regular 6"duct flattened to fit the 3.5" cavity. So my assumption is that the second floor registers uses individual ducts from the 2 main supply lines. But I could be wrong.

    Registers (evenly spaced and most in the floors and the rest low on the walls (in bathrooms)): Basement 7, 1st floor 9, 2nd floor 8 (all 4x10 or 6x10)
    Returns: Basement - a 8" and 6" round, 1st floor 9x8", 2nd floor 13x8 ( I can easily widen the 1st floor one to 13x8")
    Thank you for the quick response. You did well, I understand. The main problem that jumps at me is the oval supplies to the second floor. A 6" round pipe will supply about 110 CFM. The oval that you have supplies about half of that.

    So, the second floor is barely getting a (1) ton of A/C. All the other pipes (1st floor and basement) I think should be round. That would give you enough supplies for a 3.5 ton, not a 4 ton. I'm not recommending a size yet, I'm just point out your ductwork problems.

    I need more help understanding the return air. I get the 6" and 8" pipes (350 CFM). Is the 9"x8" and the 13"x8" duct sizes or grille/register sizes?

  6. #6
    Join Date
    Jul 2013
    Posts
    21
    Quote Originally Posted by George2 View Post
    Is the 9"x8" and the 13"x8" duct sizes or grille/register sizes?
    Both registers are 15x15", so the sizes I supplied are the actual duct sizes. They both sit on a sort-of central return "column" that runs straight down to the AH (this return terminates in the attic [I sealed it up last year as it was full of holes/gaps in the attic] and runs straight down to the AH. That's why I can easily widen the 1st floor return - no ducting needed.

  7. #7
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,701
    Quote Originally Posted by fstr View Post
    Both registers are 15x15", so the sizes I supplied are the actual duct sizes. They both sit on a sort-of central return "column" that runs straight down to the AH (this return terminates in the attic [I sealed it up last year as it was full of holes/gaps in the attic] and runs straight down to the AH. That's why I can easily widen the 1st floor return - no ducting needed.
    Okay, thanks. So, for the guys (experts?) that want to put in the 4 ton......you have about 3.5 ton (1,400 cfm) of airflow with all the 1st and 2nd floor registers wide open. It makes it awfully hard to balance the airflow, huh?

    Where it gets even more ugly is on the return side (as often it does). You have less than 3 ton of return. About 1,165 cfm. A 4 ton system needs 1,600 cfm.

  8. #8
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,701
    I've was in sales for 30 years after becoming a journeyman. I learned from the best. I've heard the line "the ductwork is okay" a hundred times. Then I take the time to show the homeowner the problems. But to me, that was the fun part of the job.

  9. #9
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,989
    Its regular 6"duct flattened to fit the 3.5" cavity. So my assumption is that the second floor registers uses individual ducts from the 2 main supply lines. But I could be wrong.
    Those 3.5" cavities could be a real problem to overcome...

    You need a MANUAL D RUN to see what can be done to provide enough ASP (Available Static Pressure) to the diffusers on 2nd floor.
    The takeoff areas & runs going to the 3.5" cavities may need considerable enlarging, with reducers at the correct points, to get enough pressure to & through those critical cavities...

    In the situation you are describing; you do not increase the tonnage of the system, however, you could if needed, increase the tonnage of the air handler's potential to generate static pressure airflow; that may not be necessary either.

    The way to provide more static to the supply air side is to reduce the negative on the return side to the entry of the blower wheel.

    That includes everything including any return air grille sizing & especially the up-sizing of Return Air filter areas to a total of 325-sq.ins., per ton of cooling to get the velocity through the filter to under 300-fpm. That will take at least 2 RA filter areas...

    If this increases the available static enough on the SA Side, with a little setting of branch dampers on ducts to the 1st floor, you might get enough airflow to the 2nd floor rooms.

    Increasing the A/C tonnage would call for more airflow & with shorter run times there could be a greater temp variation.
    Normally you usually do not oversize equipment Btuh when there are large room temp-differentials; longer runtimes are needed..

  10. #10
    Join Date
    Jul 2013
    Posts
    21
    I can see I need to find out how to calculate the CFM. And the information about static pressure is above my head.

    The main return at the AH is 12x20". Keep in mind I can enlarge or add to the return registers.

    George, you mention 1st and 2nd floor registers wide open. What about basement registers?

  11. #11
    Join Date
    Jul 2013
    Posts
    21
    Update on the returns: I figured based on previous comments that this is my limiting factor on system size and output so I opened all returns and did thorough investigation.
    First, as mentioned the main return at the AH is 12x20" So this is my max.
    The main return is divided in two (12x10" each). The one part of the return terminates on the 1st floor and the other on the second with openings of 9x8" and 13x8" respectively. Thus both registers are less than the duct they run through.
    The basement 6" return branches into the 8" return duct (so max between the 2 is 8", not 6" plus 8"). But better yet, the 8" duct splices into the return coming down from the 1st floor.

    Can someone please tell me the max cfm based on this info?

    I'm thinking I can ask when installing the new system to enlarge the return and add a dedicated return for the basement so that it does not tie into the 1st floor return. In addition I can enlarge the openings for the 1st and 2nd floor to 120sq inches each to maximize the use of the return ducts. Let me know if this is viable please.

  12. #12
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,701
    Quote Originally Posted by fstr View Post
    I can see I need to find out how to calculate the CFM. And the information about static pressure is above my head.

    The main return at the AH is 12x20". Keep in mind I can enlarge or add to the return registers.

    George, you mention 1st and 2nd floor registers wide open. What about basement registers?
    I'm not at home, so I'll have to write later on the return issue. Regarding the supplies being left wide open, that is the only way the 3 ton will work. But for balancing sake, with properly sized ductwork, you could close some of the 1st floor supplies to get more A/C to the 2nd floor.

    Obviously, the basement gets all the cold air it needs, so those registers stay closed during the summer.

  13. #13
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,989
    I can see I need to find out how to calculate the CFM. And the information about static pressure is above my head.
    It is actually very simple;[B] I have tested it numerous times; reducing the negative pressure on the Return suction side increases the airflow to those rooms needing it on the Supply side...the blades of the blower wheel are not in any way starved of air to push into the Supply Air plenum; which also ultimately pushes more air back to the blower's intake; result a lot more airflow where you want it with the same air handler/blower
    I know you understood that...the rest depends on duct size, diffusers, possible 90 turning vanes, etc.

    It needs the bulk of the Return Air Area in the rooms where it needs the most airflow to & from those rooms & very little where there is plenty of airflow now.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event