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  1. #1
    Join Date
    Jan 2005
    Location
    Dallas, TX
    Posts
    154

    Confused

    We are down to a final decision on our home -- the thermostats.

    - two 44k Carrier Performance-80 (58CTA series) dual stage burner, 3-speed blower furnaces
    - two 3 ton 12 SEER Performance-12 A/C units w/ TXV's on the coils.

    We are not using Infinity because our EnergyWise sizing for our ICF house states 40k furnaces and Infinity only come as small as 66K.

    So, for t-stats it's now Infinity vs. Thermidistat Programmable. I know the benefits of the Infinity w/ an Infinity variable blower -- we can't have that. So, here's where I am confused...

    The furnace talks about "ComfortFan" and how it "lets you control fan speed during continuous fan operation with the thermostat." But, the Thermidistat fan control is 'on/off/auto.' The Infinity fan control is 'low/med/hi/off/auto'

    So does ComfortFan work with either t-stat, and if so how?

    And if it works with a Thermidistat, then is an Infinity just overkill dollars to use w/ a 58CTA?

    Thanks!

  2. #2
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,304
    From what I've read in the past, to change the fan speed, you just switch the fan switch from on to auto, back to on, that'll change the fan speed.

    So each time you make a switch, it goes up the next speed.. When it switched again, it'll drop back down to low speed.

  3. #3
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Thermdistat and Infinity is a waste ,without the variable speed indoor fan,IMHO.

    You coul go with a 90%,58MVP furnace in the smaller size or use the 58CVA070-12,input=66,000high &43,500low.

    But the output is 54,000 high & 35,000 low.

    Is 40,000 the actual "load" or the furnace size needed?

    i.e. input versus output

  4. #4
    Join Date
    Jan 2002
    Location
    Ft.Worth,Tx
    Posts
    4,581
    I agree with dash, go with variable drive or just use a programable thermostat..Waste of money without variable drive,buying Carrier Humidistat.
    "Everyday above ground, is a good day".
    "But everyday that you have made a difference in someones life, may insure you stay above ground a little longer".<aircooled>

  5. #5
    Join Date
    Jan 2005
    Location
    Dallas, TX
    Posts
    154
    Originally posted by dash
    Thermdistat and Infinity is a waste ,without the variable speed indoor fan,IMHO.

    You coul go with a 96%,58MVP furnace in the smaller size or use the 58CVA070-12,input=66,000high &43,500low.

    But the output is 54,000 high & 35,000 low.

    Is 40,000 the actual "load" or the furnace size needed?

    i.e. input versus output
    There are three reasons we did not want to get into 96% units:
    - From what I have read and been told, I really don't think the extra money is worth it down here in our mild winters.
    - 2nd furnace will be in unconditioned garage space -- I thought 96% units had to be in conditioned space?
    - stacks through roof are already in place for 80% furnaces and I don't want to drill more holes through the concrete envelope for 96's.

    I'll have to check tonight -- I think 40,000 was the furnace size (at 80% efficiency), not the BTU output. But, I could be wrong.

    Assuming it is 40,000 size, making the output 36,000, would it be "energy foolish" to get the oversized 58CVA070-12? Would it be a non-issue that it would always running at the low-end 35,000 output and anything higher would rarely be needed?

    I certainly would spend the extra money for the superior humidity control if the heating side would work OK at those numbers.

    Remember, due to the thermal mass of the ICF walls, there is very little air leakage and no temperature swings like one gets with a stick house.

    Thanks!

  6. #6
    Join Date
    Sep 2003
    Location
    McKinney, TX
    Posts
    470
    Going with the 58CVA070-12 is the way to go. You will get the good humitity control in the summer and it will mostly run in low fire in the winter. There is nothing wrong with it running in low fire all of the time. Just tell yourself its extra support if we ever have a really tough winter. You can even use the infinity or thermidistat control usefully if you have that model. Its a no brainer to me.

  7. #7
    Join Date
    Jan 2005
    Location
    Dallas, TX
    Posts
    154
    Assuming it is 40,000 size, making the output 36,000, would it be "energy foolish" to get the oversized 58CVA070-12? Would it be a non-issue that it would always running at the low-end 35,000 output and anything higher would rarely be needed?

    I certainly would spend the extra money for the superior humidity control if the heating side would work OK at those numbers.
    Well, I think I can answer my own question as I have talked with our HVAC guys.

    They have said that it's actually to our advantage that, when heat is called for, the 58CVA070-12 will never likely have to run at the high end of the range, so we will not effectively be oversizing for our space. And, the fact that we have a 24ft vaulted living/dining area means that the variable speed unit will be all that more effective at conditioning that area evenly in heating and cooling seasons.

    So, we will be spending the extra money and getting two 58CVA070-12's along with two Infinity t-stats.

    Thanks very much for pointing me down this road! Anything more I should know before we take the plunge! ;-)

  8. #8
    Join Date
    Sep 2003
    Location
    McKinney, TX
    Posts
    470
    yeah, make sure the design the ductwork correctly.

  9. #9
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Originally posted by a/c-harris
    yeah, make sure the design the ductwork correctly.

    In other words,Be sure the do a Manual D,Duct Design.Manual D is from acca.org

  10. #10
    Join Date
    Jan 2005
    Location
    Dallas, TX
    Posts
    154
    Yes... we have all that... D & J.

    Thanks again gents!

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