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  1. #14
    This has been great information - Thank you!!

    I have one more question - I have a single stage Thermostat right now and am thinking about getting a 2 stage. I am sure the A/C is single stage - I assume this will work for both the 2 stage furnace and the single stage A/C but I could not find any info confirming this.

    Do you know which thermostat would work best - I found the Honeywell T8000 for $120 - is this a good deal?

    Thanks!

  2. #15
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,151
    The RGPE would best be controlled by the matching communicating stat but that is salty. 2nd best is a good 2 stage stat, like the TH8320. We don't comment on pricing. Just be sure you get the 2 stage, not the single stage and the dealer wires it up as such.

  3. #16
    Everyone has been a great help - Thank you

    I would also like to ask about combustible air - contractor said they will have to bring in 2 6" pipes to the furnace from outside for combustible air per code. My city uses the 2009 IBC/IRC and I have looked this over - it refers to requirements if you use combustible air but I cant see that it says it is required (but not the easiest documentation to read). My house was built in 1964 so is far from air tight. I did put a new roof on last year with new decking and have noticed that my attic fan pulls less air then it used to but is the combustible air really needed and required by code for an 80% furnace installation?

  4. #17
    Join Date
    Mar 2006
    Location
    Denver/Boulder
    Posts
    2,283
    Quote Originally Posted by sagcf View Post
    Hello,

    I have had multiple contractor estimates and multiple opinions on what I need and what will work correctly in my home. I am now confused.
    Very Common, Sagcf



    Question 1:
    I am thinking of going with a new Rheem 80% 2 stage Variable speed furnace 3 or 4 ton 75000 BTU but I have a 2 Ton A/C condenser with a 2 1/2 ton. The Rheen furnace is apparently 17" wide and the A/C coil is 21". One contractor said they would have to replace the A/C coil with a 17" coil - another contractors said they would be able to make the 21" coil work and there would be no air flow loss or problems.

    Which is correct and what ton size do I really need for my A/C to work without restriction?
    There may be other considerations, but if every other element of the system is appropriate, then the 21" coil would provide better airflow than the 17" coil. The reason for this is the configuration of the condensate pan inside the evaporator coil. There are complications to this statement, but properly installed, the 21" coil would be less restrictive than the 17" generally speaking

    NOTE:

    1)If there would be a benefit in redoing the return air drop or some other duct, the 21" coil might not be the best fit.

    2) as is common, people have forgotten to factor in high altitude considerations in Air conditioning. SAGCF doesn't need 800 CFM, they need more air. They need 880-960 CFM, not the "standard" sea level values.

    Question 2:
    I live in the Denver area so do I need to be sure the contractor uses a High Altitude conversion kit and adjust or replace the burner orifices?

    Thank you for any help you can provide!
    Most but not all furnaces are set for this altitude. However, changing out pressure switches to a more acceptable value is often required as part of the install.

    Unfortunately something that should always be done on an install is rarely done. Combustion Analysis and tuning.
    Combustion analysis is rarely done, and even less often, done well.


    Quote Originally Posted by sagcf View Post

    I have one more question - I have a single stage Thermostat right now and am thinking about getting a 2 stage.
    Do you know which thermostat would work best - I found the Honeywell T8000 for $xxx - is this a good deal?

    Thanks!
    If you get a two stage furnace it would be silly to have a single stage thermostat. I prefer the Ecobee, but a good Honeywell would work fine as well. I do NOT recommend "consumer grade" thermostats (this is what you buy at home depot)

    Quote Originally Posted by sagcf View Post
    Everyone has been a great help - Thank you

    I would also like to ask about combustible air - contractor said they will have to bring in 2 6" pipes to the furnace from outside for combustible air per code. My city uses the 2009 IBC/IRC and I have looked this over - it refers to requirements if you use combustible air but I cant see that it says it is required (but not the easiest documentation to read). My house was built in 1964 so is far from air tight. I did put a new roof on last year with new decking and have noticed that my attic fan pulls less air then it used to but is the combustible air really needed and required by code for an 80% furnace installation?
    There are two components to this requirement. The first dealing with the air available to the furnace for combustion. The second component comes into play when there isn't enough air available to the furnace from the first component of the code. That is where we bring in outside air to the furnace. If your contractor brought up combustion air, the odds are that you need it. I cannot be certain, but that is my guess.



    BROADER ISSUES:

    SAGCF,

    You have made mention of the size of the Furnace (75,000 BTUH) but you make no mention of how the size was picked, or any assessment of the ducts in your home.

    I would recommend that before an install take place, two technical aspects are covered.

    1) The furnace be sized according to ACCA Manual J (heat load calculation)

    2) The (TESP)Total External Static Pressure of your duct be tested. any significant issues should be reported to you. also you should have a conversation with your contractor concerning hot & cold spots in your home. Finally, your ducts should be given a visual once over (at a minimum) to look for signs of duct leakage.

    The first Item is time consuming, the second is not. Both are important in making a twenty year choice for your home.

    I hope this helps.
    What lies behind us and what lies before us are small matters compared to what lies within us.


    Two pressures, four temperatures = SUCCESS!


    Boulder Heating Contractor


    For Consumers:

    For HVACR Professionals:


  5. #18
    Join Date
    Mar 2006
    Location
    Denver/Boulder
    Posts
    2,283
    Quote Originally Posted by second opinion View Post
    Type in darctangant in the directory on this site. He is in Denver/Boulder. Quite knowledgeable
    Thanks for the mention SO!
    What lies behind us and what lies before us are small matters compared to what lies within us.


    Two pressures, four temperatures = SUCCESS!


    Boulder Heating Contractor


    For Consumers:

    For HVACR Professionals:


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