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  1. #27
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    5,990
    Quote Originally Posted by wally_walrus View Post
    Sorry, I'm at it again... Here are the numbers:

    Component Btuh/ft² Btuh % of load
    Walls - ---- 1.3 --- 8927 --- 20.9
    Glazing --- 30.6 ----- 5941 --- 13.9
    Doors - ---- 9.4 -- ---- 548 --- 1.3
    Ceilings --- 2.5 ----- 2158 --- 5.1
    Floors - --- 5.5 ----- 4694 --- 11.0
    Infiltration-- 37.1 --- 9391 --- 22.0
    Ducts ------- --- --- 0 --- 0
    Hydronic --- --- ---- - 0 --- 0
    Humidification ------ - 0 --- 0
    Ventilation ----- --- 11016 -- 25.8
    Adjustments ---- -- -- 0
    Total -------------- 42674 --- 100.0

    So what does everyone think of a slightly undersized two stage 40K input 39K output, given ventilation won't ever reach 120CFM and HRV efficiency is ~50%?

    Is this reason to put a disclaimer in the contract that warranty might be affected? I'd like to purchase an extended warranty
    42,674
    -5,500
    37,174 < 39,000 BTU/Hr
    __ + you have additional baseboard heater.


    + Walls: 8,927 BTUh/ 1.3 Btu/Sq Ft = 6,867 sq. ft.

    1,800 sq. ft condo with one side attached will only have about 1,400 sq feet of exterior walls. __ So, something seems to be incorrect here.
    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

  2. #28
    Quote Originally Posted by 54regcab View Post
    Can it be set to automatically do so below a certain outdoor temperature?
    That would be awesome, and it's interesting that you asked - I just recently read the PDF manual for the VP IAQ on Honeywell website and one feature was that you can lock out ventilation above and / or below a certain outdoor temp. But mine does not have that option in the menu (possibly older firmware? I've had it for about 4 years), or it is disabled due to other setting

  3. #29
    Quote Originally Posted by dan sw fl View Post
    42,674
    -5,500
    37,174 < 39,000 BTU/Hr
    __ + you have additional baseboard heater.


    + Walls: 8,927 BTUh/ 1.3 Btu/Sq Ft = 6,867 sq. ft.

    1,800 sq. ft condo with one side attached will only have about 1,400 sq feet of exterior walls. __ So, something seems to be incorrect here.
    I don't know how he came to this figure, but I provided the blueprints of the house, also mentioned it is a two storeys and has a basement. Are the basement walls supposed to be included in the square footage?

  4. #30
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    5,990
    Quote Originally Posted by wally_walrus View Post
    I don't know how he came to this figure, but I provided the blueprints of the house, also mentioned it is a two storeys and has a basement. Are the basement walls supposed to be included in the square footage?
    Basement walls are typically exposed to ground which is about minimum of 45'F, not -10'F.

    Q = A * dt /R
    A = ~ 900 sq. feet
    dt = 70 - 45 = 25 with walls entirely below grade.
    R =~ 5, unfinished
    Q =~ 4,500 BTU/Hr, IF R =5, half that if basement is finished with R>10.
    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

  5. #31
    Quote Originally Posted by dan sw fl View Post
    Basement walls are typically exposed to ground which is about minimum of 45'F, not -10'F.

    Q = A * dt /R
    A = ~ 900 sq. feet
    dt = 70 - 45 = 25 with walls entirely below grade.
    R =~ 5, unfinished
    Q =~ 4,500 BTU/Hr, IF R =5, half that if basement is finished with R>10.

    Thanks for pointing this out! I just emailed him asking this very question

  6. #32
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,632
    Quote Originally Posted by 54regcab View Post
    IMHO you won't even need the room heater, I think man J has enough fudge factor built in to cover the colder than design temperature nights.
    Sounds like a tight enclosure with no load left or right, and you want energy bill bragging rights? I mean, sounds like you are already assured of hitting the black circle, you are now dialing the sight to hitting DEAD CENTER?

    Which furnace goes lowest? Don't some 60's drop to 20? (my car might go 100, doesn't mean I ever drive it that fast. Look to turndown)

    I would DEFINITELY remove the thermostat from decision making bias. This is a 15-20 year decision, to me specifying a non communicating stat would require a LOT of convincing.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  7. #33
    Quote Originally Posted by tedkidd View Post
    Sounds like a tight enclosure with no load left or right, and you want energy bill bragging rights? I mean, sounds like you are already assured of hitting the black circle, you are now dialing the sight to hitting DEAD CENTER?

    Which furnace goes lowest? Don't some 60's drop to 20? (my car might go 100, doesn't mean I ever drive it that fast. Look to turndown)

    I would DEFINITELY remove the thermostat from decision making bias. This is a 15-20 year decision, to me specifying a non communicating stat would require a LOT of convincing.
    Hi tedkidd, I did search through many tech specs but none of the 60K two stage that I could find does LESS THAN 65 - 70 % in low fire. If they came in the 35 - 40 % my quest would have been over. I read some of your blogs elsewhere and see you're a big proponent of sizing to match the load, you actually mean modulating (with a communicating stat) is the ONLY way to achieve this?

    I would still like to hear your clear opinion on a slightly undersized two stage unit

  8. #34
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    3,948
    I'd look really close at the rheem/ruud/thermalzone 45k in/42k out 2 stage furnace with variable speed blower.

  9. #35
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,632
    Since manual j seems to oversize using a .77 factor, how would you define undersize?

    If it were me, I'd do it all day.

    Will you be leaving the thermostat alone or using setback?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  10. #36
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    3,948
    Quote Originally Posted by tedkidd View Post
    Since manual j oversizes be so .77 factor, how would you define undersize?

    Will you be leaving the thermostat alone or using setback?
    Oversizing just so that you can do setback makes no sense to me...

  11. #37
    Quote Originally Posted by 54regcab View Post
    I'd look really close at the rheem/ruud/thermalzone 45k in/42k out 2 stage furnace with variable speed blower.
    Quote Originally Posted by tedkidd View Post
    Since manual j seems to oversize using a .77 factor, how would you define undersize?

    If it were me, I'd do it all day.

    Will you be leaving the thermostat alone or using setback?
    Quote Originally Posted by wally_walrus View Post
    So what does everyone think of a slightly undersized two stage 40K input 39K output? Is there a way to interlock an additional heater (electric perhaps) to the furnace so that it adds a couple K BTU on the coldest day? Or the only solution is manually turning an electric heater ON? I'm trying to stay with the contractor that seems the most competent, but even he (the salesman) is hesitant going with 40K

    Like mentioned I could also reduce the ventilation, as well as will replace the water heater with a High Eff. direct vented model and will be able to close off two more holes in the envelope (make up supply air and chimney)

    Unfortunately we don't have a lot of choices when it comes to contractors up here, most customers are government employees clueless and with large pockets
    By "undersize" I mean 39,000 output on a 42,674 load (calculated using significant fudge factor). But I get your point, I just have to convince my contractor that that's what I want

    I'd love to find a GOOD Rheem installer up here, unfortunately there's only 3 listed and was advised by someone in the industry to stay away from them. I actually asked the contractor I've been working with for some time if he would be comfortable installing a 45K Rheem for me (he says Rheem is over-the-counter so anyone with a license can get it). Important - How can I get an extended (10 years) labour warranty with Rheem?

    I will most likely leave the thermostat alone, but figured even if I was using setback my VisionPro IAQ (with outdoor temp sensor) does Intelligent Adaptive Recovery so will figure out how long in advance to start recovering (if it will setback at all)

    Thanks everyone

  12. #38
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    3,948
    Most manufacturers require you to register your product within 30 days of installation to get the extended warranty.

  13. #39
    Quote Originally Posted by 54regcab View Post
    Most manufacturers require you to register your product within 30 days of installation to get the extended warranty.
    From what my contractor told me, Rheem is an over-the-counter product and not dealer-only, so that's why I don't know how to actually buy the extended factory warranty. Is this something only the installer can order on my behalf? I understand it needs to be registered in order to be valid

    Also what's the best way to find how is parts distribution and availability for Rheem in my area?

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