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  1. #1

    New HVAC installation - advice

    This forum and the pros that contribute are excellent. What a tremendous resource. I've read a ton of posts to help with a BIG decision i have to make in a few weeks. There are many posts about similar situations but none exactly like mine. Below is a brief description of my situation. Hopefully there are some of you out there that can steer me in the right direction.

    Background:
    I live in Houston, TX and am buying a house that was built in 1962. It is a 1.5 story ranch with 3376 total sq ft (2217 sq ft downstairs, and 1159 sq ft upstairs). The front faces north and trees shade about 1/3 of the house. There are approx 13 windows down and 6 up; most are single pane with some of the larger ones being double pane. The existing Amana HVAC system was installed in 1993 and has a single 5 ton condenser and 80,000 btu furnace. The furnace/airhandler is located in the top attic. Ducts are the original insulation-wrapped tin and are in good shape. I have not lived in this house and have no idea how it heats and cools with the current system. We are having new insulation installed in the attic so it will be up to current r-value standards.

    Situation:
    The Amana system is shot and needs to be replaced before next summer. I plan on having a new system installed when we move in, which is where the dilemma starts. I am on a limited budget so money is factor, but so is comfort. I want to find the happy medium between comfort and cost. We plan on being in the house for a while.

    Here are the conclusion's I've made so far:
    1) I definitely want a 2-stage condenser coupled with a variable speed air handler.
    2) I like the Trane system in my current house. It's a XL19i and has been bullet proof. I wouldn't mind staying with Trane.
    3) I'd like to keep the existing ducts since they are in good shape and to cut down on cost.
    4) The sq ft of the house is right on the cusp of being too much for a single 5-ton unit.
    5) We've had 2 HVAC companies look at the house and are awaiting quotes. Both felt that a single system properly zoned will work.

    Here are my questions:
    1) Are the conclusions mentioned above accurate?
    2) Will a single system with 2 zones (upstairs on one zone and downstairs on the the other) adequately cool the house?
    3) If I go with a zoned system how can I know it's being installed correctly?
    4) Should I broaden my scope outside the Trane name?

    I am just at a loss for what to do. I don't want to make a bad decision and regret it later. But i also don't want to break the bank. Any advice or guidance you guys can offer is GREATLY appreciated. Thank you in advance for your time.

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,238
    Two heat pumps
    unless you find someone who KNOWS and IS EXPERIENCED AT ZONING
    __ DESIGN __ INSTALL __ & CONTROLS __

    ___You may be suprised at the
    __ 'low' cost difference between two systems
    __ and one system with zoning THAT NEEDS significant duct modifications.
    _______________________ INQUIRE. ____________
    Or does one system with zoning cost more?

    Heating requirements are rather small with ~1,000 Heating Degree Days (HDD)

    Station: HOUSTON HOBBY AIRPORT, TX, US (95.28W,29.64N)
    Station ID: KHOU
    ………
    Month
    ___Starting .. HDD …… CDD (Cooling Degree Days)
    4/1/2010 … …est…… 300
    5/1/2010 … …est…… 400
    6/1/2010 0 ……… 547
    7/1/2010 0 ……… 560
    8/1/2010 0 ……… 640
    9/1/2010 2 ……… 465
    10/1/2010 40 ……… 267 3,179
    11/1/2010 179 ……… 88
    12/1/2010 294 ……… 49
    1/1/2011 376 ……… 14
    2/1/2011 317 1166 76
    3/1/2011 70 ……… 148
    4/1/2011 22 ……… 311
    5/1/2011 13 ……… 396
    6/1/2011 0 ……… 592
    7/1/2011 0 ……… 624
    8/1/2011 0 ……… 695
    9/1/2011 0 ……… 497 Annual
    10/1/2011 46 ……… 247 3,362
    11/1/2011 152 ……… 119
    12/1/2011 314 ……… 31
    1/1/2012 216 ……… 53
    2/1/2012 192 874 50
    3/1/2012 55 ……… 176
    4/1/2012 14 ……… 258
    5/1/2012 0 ……… 404
    6/1/2012 0 ……… 550
    7/1/2012 0 ……… 531
    8/1/2012 0 ……… 607
    9/1/2012 1 ……… 398 Annual
    10/1/2012 69 ……… 216 2,964
    11/1/2012 136 ……… 114
    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
    dan sw fl - thanks for the feedback. Curious why 2 different authorized Trane "comfort specialists" would tell me a single 2 zone system would be adequate.

  4. #4
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,145
    You are better off with 2 lower end systems than a single high end system, for both comfort and energy use. Work WITH the physics of "heat rises". You will run your A/C upstairs much earlier in the year than the downstairs. Reverse is true for heat, you won't need to turn on upstairs heat until it gets really cold outside. In Houston you might not even need heat upstairs at all.

    You could do a 2 ton heat pump upstairs since you won't use much heat. A Straight A/C with heat strips might even make more sense depending on installed cost difference and electric rates. You would have to determine payback time for each option. I'd go with the highest SEER single stage system (14 or 15 for most brands). Downstairs a 45k furnace with a 2 ton A/C. Not much need for A/C on the lower level and the gas furnace makes sense downstairs for heat.

    All system sizes are guesses, you will need to have a proper load calculation done to get correct size. Don't let contractors oversize you because they are scared to correctly size.

  5. #5
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,238
    Quote Originally Posted by crudedude View Post
    dan sw fl - thanks for the feedback. Curious why 2 different authorized Trane "comfort specialists" would tell me a single 2 zone system would be adequate.
    They are Not incorrect.

    There are at least a half dozen configurations that may ' be adequate'.

    2 systems follow the KISS principle better IMO.
    _____ K eep I t S imple & S incere. ______

    The Odds that more contractors can install 2 systems THAT WORK than
    _____________ Those Contractors who can install properly functioning Zoned systems is Enormous.
    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

  6. #6
    Great feedback. Thank you! So the consensus thus far is for separate systems. Can I use the existing duct work and modify it or does it need to be replaced (keeping cost in mind)?

  7. #7
    Not sure if recommendations are allowed. If they are, I am open to suggestions for a good and fair HVAC installer in Houston.

  8. #8
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,145
    You might be able to use the existing ductwork, or at least some of it. Depends a LOT on the existing installation.

  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,238
    Quote Originally Posted by crudedude View Post

    Great feedback. Thank you!

    So the consensus thus far is for separate systems.

    Can I use the existing duct work and modify it or does it need to be replaced (keeping cost in mind)?
    Consensus, L.O.L. 2 replies, sure?

    I'd say if one has 20 common responses out of 30 on an issue, one might call it a majority [ given there are Only 2 options].

    Consensus - I doubt that word can actually be applied to HVAC situations, and certainly not in ANY Internet Forum.
    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

  10. #10
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,517
    Limited budget and 2 speed Trane usually aren't used in the same sentence. Nor are putting 2 systems of any type in. My advice would be to move in and see what the issues are, then proceed. A 5 ton in 3300 sq. ft. in Houston, with single pane windows and bad insulation is at the very best stretching it. Unless you like your house 80 during the dog days of summer.
    I like DIY'ers. They pay better to fix.

  11. #11
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,145
    Quote Originally Posted by bmathews View Post
    Limited budget and 2 speed Trane usually aren't used in the same sentence. Nor are putting 2 systems of any type in. My advice would be to move in and see what the issues are, then proceed. A 5 ton in 3300 sq. ft. in Houston, with single pane windows and bad insulation is at the very best stretching it. Unless you like your house 80 during the dog days of summer.
    4 of the 5 tons will be sent downstairs and it will stay cool. It's the upstairs that will be roasting all summer.

  12. #12
    Join Date
    Apr 2010
    Location
    NC Sandhills
    Posts
    391
    is house on a slab or crawspace? Are the downstairs registers in the floor, sidewall or ceiling? With the age of the house I am sure the infiltration on the ducting will be high. I do not see a need to buy high SEER equipment and not address the other issues. Adding insulation is nice but will not help air leaking from ducts, are they accessable? Trane has the best zoning there is (IE no by-pass) but it only works with their higher end equipment and uses a variable speed blower with fully modulating dampers, and I doubt that will jive with your budget. I like zoning with smaller 2 story homes, but a house your size I would put in seperate systems. Ask the contractors for bids both ways even ask the ones who have already been out for a new bid with 2 systems. The price difference may not be as much as you think.

  13. #13
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,137
    with two systems duct work modifications will need to be done.
    returns will need to be added.

    so add that to the cost also.

    beware of companies that want to put 3 tons system upstairs
    and 4 tons downstairs. you'll get bids for that.

    I'm a big fan of zoned systems..one unit multiple t-stats,
    not multiple units. this may also be an option if you find someone
    experienced in these installs.

    from experience I know that we can heat & cool with one unit...
    if the house is air sealed, and ductwork is sealed.
    testing both would be my first step..before adding insulation
    in attic. once you add insulation..its going to add to the difficulty
    of air sealing.

    are any of the upstairs walls shared with the attic?
    if so the first step would be to insulate the walls
    then air seal them. see link of comprehensive air
    sealing details. pay attention to attic kneewalls..
    this would be similar to any attic walls shared with attic.

    http://www.southface.org/default-int...gkeypoints.pdf

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

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