Help with replacement system, partial vs total, choice...
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  1. #1

    Help with replacement system, partial vs total, choice...

    Hi, this is my fist post, hope I include all the relevant info - this forum is super informative.

    I live in Houston, TX in a 2 story townhouse.

    House has 2 A/C systems (upper floor about 900 sq ft). The upstairs system (original, 13 years old) is a 10 SEER, 3.5 ton condenser, 4 ton furnace, and evaporator. The fan motor on the condenser is new and the system needed some freon 2 years ago and new capacitor (twice I think in the last 3-4 years).

    For upstairs, the plenum and evaporator areas have a lot of mildew as well as poor seals (gaps between parts in the attic) and I finally decided to do something (replace them). I am also a bit worried of the air quality. I use the 3M Ultra allergen filters in the return (30x20x1).

    My first dilemma is this:
    1. should I just replace the plenum and the evaporator to eliminate the existing mildew? This does not sound like it's going to eliminate the cause.
    OR
    2. Should I replace the evap and furnace with a variable speed unit with humidity sensor that would adjust the aiflow, hopefully preventing recurrence thereof

    My 2nd question:
    If i go for the furnace+evap, should I do the whole system? I expect we'll be in this house 5-7 more years, so if the current system is going to break during that time, I might as well change it. On the other hand I have a home warranty that will probably replace the compressor when it breaks.

    I talked with 2 companies listed in the EBSCO Research Best Pick report and they both described good quality work and quoted me 2 systems (to choose whatever parts I want):

    1. American Standard
    Furnace AUD2B080A9V3VB
    Evap. 4TXCB036BCH
    Condenser 4TTB4036E1000B
    Honeywell 8000 control panel
    Tech told me they install a humidity sensor in the furnace outlet that will be used to adjust fan speed as needed (var speed)
    Plus resealing all air outlets at drywall and the 2nd A/C unit (I asked for this)

    2. Carrier
    furnace md# 58cva.
    coil: csphp.
    controller will be the infinity - can also dynamically adjust blower speed to control humidity
    Plus same resealing as above
    Did not give me the P/N for the condenser, since I had primarily asked for the furnace + evap

    Carrier system (2nd company) is 3-4 thousand more expensive than the other -- why? is it worth it? (not sure if I'm allowed to post the actual price quotes). My electricity bills are not too high, so efficiency is not a big issue.

    It's a big chunk of money, so I would appreciate any advice/guidance on:
    - what should I replace?
    - Which system is a better value
    - anything important I am missing / missunderstanding?
    - anything else to ask the contractors?

    Thanks a lot in advance.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    Tech told me they install a humidity sensor in the furnace outlet that will be used to adjust fan speed as needed (var speed)
    Sounds like a cheapo humidifier humidistat hooked to the dehumidify on demand terminals of the furnace. It works but the Infinity control is certainly a lot more sophisticated. At least if you go Trane, get a Vision Pro IAQ or the like from the others.

  3. #3
    Join Date
    Jul 2006
    Location
    Virginia
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    4,600
    why in the crap are they wanting to put a 80000 btu furnace on 900 square ft also highly unlikely you need 3 tons of cooling I would want some one to perform a load calc and put in a correct size unit
    We really need change now

  4. #4
    Sorry, just realized my mistake: the upstairs is about 1200 sq ft, downstairs about 900 (+ garage). (not sure how to edit the original post)

    I am quite ignorant of this, what do you mean by "A Vision Pro IAQ" or the like.

    Any more insight on my questions? partial vs. whole system? One much better than the other?

    Thanks for the help.

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    A Vision Pro IAQ is a control by Honeywell with lots of features beyond what a regular thermostat has. In your case, it will stage the 2 stage gas furnace properly. But it will also work with the variable speed blower for extra dehumidification. Would be a lot nicer than a cheap humidistat in the return as the American Standard dealer is suggesting.


  6. #6
    Join Date
    Jul 2006
    Location
    Virginia
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    baldloonie is correct I would skip the humidistat and go with the iaq thermostat also still think that 80000 btu furnace is way to big .
    We really need change now

  7. #7
    BaldLoonie, catmanacman,

    Thanks for your help. I will ask for the IAQ control and also about a smaller size furnace. I think I'll go with the

    I have looked through the controller manuals and it seems to me they all have a simple relay connection to control the blower. What I don't understand is this: how is the variable speed controlled/varied? and how is the humidity controlled without changing or lowering the temperature (too much)? I would imagine by decreasing the airflow the air would cool more, thus extracting more water, but would not cool the house a lot more because of the reduced airflow...

    Would you please explain to me the different ways to dehumidify (or link to a resource) - preferably without lowering the house temperature much -- my main goal is to have less humidity in the system and minimize mildew... We usually keep our thermostat at 75-77 in the summer, and Houston is quite humid...
    Thanks.

  8. #8
    Join Date
    Jan 2004
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    Lancaster PA
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    Slowing the air flow doesn't lower the air temp proportionally, so it doesn't cool the house faster, but it does remove more moisture from the air.
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  9. #9
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    Teddy bear will probably weigh in on this one. It sounds like you would benefit from a whole house dehumidifier and to offset the added cost of the dehu you could go with a lower efficiency model (13/14 seer). A whole house dehu is the only true way to maintain a constant less than 50% humidity inside the home. Better Insulating and sealing the ductwork generally gains you better efficiency than a high end system. Also sealing up the house so that the outdoor humidity can't get into the house in the first place is a good step to better iaq. Check out this site www.comfortinstitute.org I would recommend changing all the components due to the EPA forcing the change in refrigerent a from r22 to r410a, soon you won't be able to get a r22 condenser and r22 refrigerent is getting astronomically more expensive while r410a is getting cheaper. If the compressor goes out in a few years and the r22 inside is lost or unusable due to contamination it may be cheaper to change everything out than to recharge with R22 and a new compressor. Hope this helps good luck

  10. #10
    Thanks for the suggestion. I have been reading through this site for hours and it seems this may be the best time to rethink my whole approach:

    So I will replace the whole A/C system for the upstairs but want to install something that makes sense and gives me the best IAQ.
    (checked actual living space sq ft: upper 1500 sq ft - 3 bedrooms, down: 940 sqft. House occupied mostly evening+night. Also, I am almost positive my house has no fresh air line)

    Based on the suggestions above and other posts on this site (esp. some of Teddy bear's posts) it seems a good solution for me may be:
    - ask the A/C contractor to run a new load calc, measure my leakage and reseal all ducting
    - install new complete A/C for upstairs with var. speed furnace, humidity controller (e.g. the Honeywell VisionPro IAQ), and a simple/low eff single stage compressor (in Houston it will run a lot during the summer, spring and fall, very hot and very humid most of the time).
    - to this add a whole house ventilating dehumidifier with a CO2 controller - how should I plumb this? - i saw a suggestion for intake from upstairs return (and fresh air as well, i assume) and output into the lower level (or both?) A/C ducting (plenums?).
    -- how does the ventilating dehum tie in the A/C control?

    Please let me know if this makes sense, any other suggestions, what would be a good setup for me, etc. How should I approach the contractors about this job, what should I ask them to do/design/propose? It's quite different from my initial request to replace the evaporator & furnace.

    Thanks a lot.

  11. #11
    Any thoughts on the best setup for Houston? Since i live in the middle of the city, outside air quality can be pretty poor during hot, moist, polluted summer days, so i was thinking, does it make sense to seal the house well and only bring fresh air late night?

    Also, how can I evaluate the contractors for quality of work and knowledge? I have read user reviews, but they are not too helpful... I asked the technicians about how they will install the system and was satisfied with what they said, but is there a better way to evaluate quality? Both are NATE certified, BBB well rated.

    I am trying to get as knowledgeable as possible before talking with the contractors again (the new system would be about $k and want to make a good decision). Thanks.
    Last edited by beenthere; 11-27-2012 at 04:38 PM. Reason: price

  12. #12
    Join Date
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    This is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.

    Further infractions may result in loss of posting privileges.
    Last edited by beenthere; 11-27-2012 at 04:38 PM. Reason: Non Pro * Member

  13. #13
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    jefft72, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.

    Your post has been deleted.
    Further infractions may result in loss of posting privileges.
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