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  1. #1
    Join Date
    Jul 2008
    Posts
    7

    Looking for a Second Opinion.

    This is kinda long - so i'll break it up into sections for you....

    Background Info:
    Let start by saying this is my first HAVC system I’ve ever had to purchase so I only know what I’ve read in regards to the various systems and the specs.

    Anyway – our current system is running a bit inefficiently and our electrical usage has gone up (not just the cost but the actual KW hours) over the past few years and continues to go up despite improvements we have made which included new dual pane windows.

    The current system is pushing at least 13-14 years old (it came with the house). And to make things worse, we have added square footage and re-configured a few walls since we moved in here 10 years ago. With that said – we decided to replace the roof mounted Heat pump.

    Size and Location
    The house is currently at about 2150 Sqft – dual pane windows throughout and is reasonably to well insulate. The house is located in the Metro Phoenix, AZ area

    The Search For a Contractor
    We started our search for a new system by calling in about 4 different companies and having each take a look at our house and suggest a new system and any changes (within reason) that may need to be made.

    Long story short (well not so short…) we are about 99% settled on a contractor that we feel comfortable with and checks out well with the BBB. The price was good (not the lowest, but not the highest either)

    Settled on a Contracor
    They suggested a few things the others didn’t suggest or flat out said we didn’t need. After doing some research (some on this site) I think what this contractor is suggesting makes sense and will be effective. But since I’m no expert, I figured I would ask the experts for a second opinion


    The Specs
    So here goes.

    Suggested unit:
    5 Ton
    2-stage heating and Cooling
    R-410A


    Suggested Changes:
    - Replace existing return for a larger grill
    - Added a second return
    - Total (combined) return are size - around 144sq inch

    - Add an additional vent to the master bedroom

    - Cut in a new roof jack for side by side configuration (current one is too small and is an over/under configuration)
    Replace the main trunk to the existing return air for a larger diameter and to accommodate the new return air.

    Attached to this post is a PDF of a quick drawing I did of the house with the location of existing vents and return air. It also shows the location of the new vents and the second return air. And… (is this enough info yet ) I also made an approximation of the layout and location of the duct work based on some basic visual inspection in the attic.

    Anyone want to take a shot at this and give me a second opinion?

    Thanks in advance
    Attached Images Attached Images
    Last edited by Tono; 07-24-2008 at 11:36 PM. Reason: spelling :-)

  2. #2
    Join Date
    Aug 2003
    Location
    Lincoln, Nebraska
    Posts
    1,051
    How did they determine the size of the unit? If it was done properly then it sounds like they have taken the time and effort to design a system that should work for you.

    The most important thing is to find a contractor that you are comfortable with. It sounds like you are on the right track.
    Its a good Life!

  3. #3
    Join Date
    Jul 2008
    Posts
    7
    Thanks for the reply...

    All but one of the contractors we had come out did the basic measurements of the overall house size and measured the existing return air grill as well as counted the windows.

    The particular contractor that we will likely go with went a step further and actually measured the size of all the windows (instead of just counting them) and then took the information he gathered back to their office and ran the info through some sort of load calculation program.

    After a few days they presented us with the actual printouts and work sheets they used to calculate the size unit we needed. They also gave use 2-3 options on the unit that fit the requirements and a rundown of the changes they where suggesting for the new vent and return grill.

    I should also note – that all the contractor that quoted on this all came back with a 5 ton unit – regardless of how they chose to calculate it.

    We like the contractor and we are comfortable with them – so I was just looking for a some confirmation we are making the correct choice in both unit size and duct changes since I have very little experience with this sort of thing…
    Last edited by Tono; 07-25-2008 at 10:28 AM.

  4. #4
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,960

    Can the heat-gain be reduced?

    Could you make any changes in your home that would reduce the heat-gain enough to go with a 4-ton system?

    There is new safe foam insulation that also reduces air infiltration.

    Two stage helps, however, it is much easier to get 2nd stage adequate airflow & a properly heat-loaded evaporator coil on a 4-ton, rather than on a 5-ton.

    In your situation, that is what I personally would do, were it my home.

    A factor to consider is, how well would a 4-ton handle the lighter load hours? What is your response concerning the light load condition situations with a 4-ton verses a 5-ton 2-stage unit?

    I really like the blue print, BTUHs, & CFMs to each room could be on the pdf. - udarrell

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    Was the old unit a 5 ton.

    If not, are they increasing the size of your supply duct to handle the extra air the 5 ton will move.
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  6. #6
    Join Date
    Jul 2008
    Posts
    7
    Quote Originally Posted by udarrell View Post
    Could you make any changes in your home that would reduce the heat-gain enough to go with a 4-ton system?
    I’m not really sure – I do know that the attic is full of blown in insulation and it’s pretty deep – alteast 16 inches and deeper

    There is new safe foam insulation that also reduces air infiltration.

    Quote Originally Posted by udarrell View Post
    Two stage helps, however, it is much easier to get 2nd stage adequate airflow & a properly heat-loaded evaporator coil on a 4-ton, rather than on a 5-ton.

    In your situation, that is what I personally would do, were it my home.
    I’m going to meet with the contractor today – so I’ll ask those questions

    Quote Originally Posted by udarrell View Post
    A factor to consider is, how well would a 4-ton handle the lighter load hours? What is your response concerning the light load condition situations with a 4-ton verses a 5-ton 2-stage unit?
    Well – right now our old unit is a 4 ton. I have no idea what the SEER/EER rating is on it though since it came with the house and is at least 12-13 years old. During the summer, it struggles to keep the house near 80 deg both day and night. During lighter load times of year it, for the most part, works ok.

    I did have a concern about the 5ton short cycling which is one o the reasons I felt comfortable going with the variable speed – which I think helps that a bit (correct me if I’m wrong - please )


    Quote Originally Posted by udarrell View Post
    I really like the blue print, BTUHs, & CFMs to each room could be on the pdf. - udarrell
    That a good idea – maybe I can had my drawing to the contractor and get them to put that info down on the sheet for me

  7. #7
    Join Date
    Jul 2008
    Posts
    7
    Quote Originally Posted by beenthere View Post
    Was the old unit a 5 ton.

    If not, are they increasing the size of your supply duct to handle the extra air the 5 ton will move.
    Old unit is a 4 ton

    yes they are increasing the supply duct. This particular contractor was the only one out of the 4 that came out who suggested it. There quote inlcuded:

    - cutting new roof jack to accommodate a side-by-side elbow (currently have an over-under)
    - replacing main supply duct down to the existing return air (increasing the size)

  8. #8
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by udarrell View Post
    Could you make any changes in your home that would reduce the heat-gain enough to go with a 4-ton system? Two stage helps, however, it is much easier to get 2nd stage adequate airflow & a properly heat-loaded evaporator coil on a 4-ton, rather than on a 5-ton.In your situation, that is what I personally would do, were it my homeA factor to consider is, how well would a 4-ton handle the lighter load hours? What is your response concerning the light load condition situations with a 4-ton verses a 5-ton 2-stage unit?l
    when its 100 degrees outside he is gonna be upset that the system wont cool the house

    then your gonna say sorry you should of gotten the 5 ton

    the proper response to your question about light loads is

    being a 2 speed system you won't have to worry about how the system handles lighter loads

    also as stated ductwork must be able to handle a 5 ton!



    .

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    Quote Originally Posted by Tono View Post
    - replacing main supply duct down to the existing return air (increasing the size)
    The supply duct, and return are 2 different ducts.
    If replacing duct to the existing return. That is return duct, not supply.

    I would ask them about the supply duct.

    Under sized supply duct, can make your system noisey.
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  10. #10
    Join Date
    Jul 2008
    Posts
    7
    Quote Originally Posted by beenthere View Post
    The supply duct, and return are 2 different ducts.
    If replacing duct to the existing return. That is return duct, not supply.

    I would ask them about the supply duct.

    Under sized supply duct, can make your system noisey.
    OK - I had not realized that (as i said - I don't know much about it )

    I'll ask the contractor if they did any calculations specific to the exiting "supply" duct work vs just the "return" duct work and if not ask them to do so.

    Thanks for the info

  11. #11
    Join Date
    Jun 2005
    Location
    SW Wisconsin
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    4,960
    Quote Originally Posted by Airmechanical View Post
    when its 100 degrees outside he is gonna be upset that the system wont cool the house

    then your gonna say sorry you should of gotten the 5 ton
    ("The sizing of equipment ought to be thoroughly discussed & agreed to by all the resident A/C users.")

    the proper response to your question about light loads is
    being a 2 speed system you won't have to worry about how the system handles lighter loads -
    also as stated ductwork must be able to handle a 5 ton!
    My statement was to design the sizing of the equipment units & the duct system to meet the heat-gain calc load after all such load reductions have been made.

    The old 4-ton may have had many problems causing it not to effectively cool the home. The majority of the reasons that systems do not achieve their Nominal BTUH Ratings is due to lack of Best Practice Procedures during the initial installation & set-up.

    Phoenix AZ., well insulated 2150-sf home, listed summer outdoor design 107-F dry bulb 71-wet bulb, or under 25% RH, little or no outdoor humidity/latent load problem | Indoor design @ 50% RH, & 75-F; if a 4-ton will easily handle that load, we both know that we would not want to oversize to 5-ton.

    In high heat climates, the lower BTUH of the compressor compared to the condenser's BTUH Rating could also be factored into the equipment sizing equation.

    A 5-ton system demands a lot of airflow-duct-system accommodations, that are seldom easy to come by, in most residential situations. Duct system renovation can run up some rather large costs for a 5-ton system.

    I personally would Way Over-size Return-Air filter-racks, to keep the velocity & pressure drops lower, I would want two of those filter racks at Room Return entry points, even for a 4-ton system; No filter in the air handler.


    The initial cost will be considerable more for the 5-ton system, & that extra cost needs to be justified in every arena. Investments Reducing the heat-gain will reduce both A/C & heating utility bills; in that Phoenix climate heating should be minor compared to A/C costs. - udarrell

  12. #12
    Join Date
    Jul 2008
    Posts
    7
    Well - had my meeting with the contractor today and I feel we made the right choice. I went through all the questions and suggested raised in this thread and he was very willing to answer all my questions. He also explained everything – even created a few rough sketches to illustrate the changes they will be making to the duct system. I even had him go through his work sheets they created and explain how they came to the figures they did and it all seems to make sense.

    In regards to udarrell, I did bring up your thoughts on this, and after looking over the calculations, it did show the unit to by slightly oversized. I don’t remember the exact numbers but it was not excessive.

    For me this was OK though – because we seem to do some sort of remodel to the house about every year and half or so, and at some point, I know we will be adding more Square footage to the master bedroom and bath… It’s inevitable…

    Anyways - I went over the drawing with him and had him explain the exact changes/modification they will be making to the duct system and why each change was needed. I may update the illustration since it would be easier then trying to explain it all here. But the short version is, the changes and modifications being done are to specifically address the following:

    1- Better air distribution – adding a new vent and a second return
    2 - Some modification to the exiting duct system to help with point 1, and to accommodate the higher CFM the new larger unit will produce
    3 - Increasing total supply duct and vent sizes to accommodate the larger unit

    Before he left – he went through the house took some additional measurement and re-measured the existing return. He also got up in the attic and took measurements and notes. Based on the attic inspection he also made a minor modification to the way they will be modifying the existing ducts.

    I’ll keep this thread up to date as the install proceeds late next week

    Thanks again everyone…

  13. #13
    Join Date
    Jun 2008
    Posts
    72
    may I ask what tool did you use to draw the house layout. it looks nice!

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