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  1. #1
    Join Date
    Sep 2009
    Posts
    25

    Help with HVAC-CALC home owner load calcualtion

    Hi All,
    I'm trying to do load calculation with HVAC-CALC software. As a new home owner and a first time home owner I'm trying to understand all the aspects of the calculation. The first problem I've encountered is the duct insulation. The presenter of the learning video on the HVAC-CALC website selects R6. How can I check my duct insulation rating?

    Thanks

  2. #2
    Join Date
    Sep 2009
    Posts
    25
    Actually I'm not even sure I need to add the Duct component to the load calculation. The guy on the video says "if the furnace was in the basement and the duct vent was in the condition space we wouldn't add the Duct component at all". So I guess my first question is what is this duct vent and where is this condition space? My furnace is located in the basement and I don't know of any additional vents.

    For those of you who's interested to watch the video, here is the link:
    http://www.hvacmovies.com/movies/wholehouse/wh3a.html

    Thanks.

  3. #3
    Join Date
    Sep 2009
    Posts
    25
    I'm kind of answering my own questions here. I think I don't need the Duct component because the furnace is in the basement and the duct is inside the house so it doesn't contribute to the load.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,750
    If the duct is in conditioned space. It is not part of the load calc.
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  5. #5
    Join Date
    Sep 2009
    Posts
    25
    Quote Originally Posted by beenthere View Post
    If the duct is in conditioned space. It is not part of the load calc.
    Thanks beenthere,
    I wasn't sure what the conditioned space is. I figure it's the space that is already a part of the calculation.

    Now, how would I know the cavity insulation rating? The guy in the video selects R-13, the software manual reads "Select R-11 (3 in.). This is the standard insulation in the wall cavity of a wall with 2 X 4 studs". I selected R-11.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,750
    Unless you know different.
    Use R11.
    Pretty standard here for 2X4 walls. The batts could be rated at R13. But, when you allow for the studs. You lose some R value in the wall.
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  7. #7
    Join Date
    Sep 2009
    Posts
    25
    Okay I guess I'm done. Hopefully I did the numbers correctly. The only thing that I wasn't sure of was the Ceiling insulation. Mine is R-32. The available selections were 30 or 38, so I selected 30. I got the following results:
    Design Conditions: Toronto
    Indoor: Outdoor:
    Summer temperature: 75 Summer temperature: 87
    Winter temperature: 70 Winter temperature: -8
    Relative humidity: 55 Summer grains of moisture: 95
    Daily temperature range: Medium

    Building Component

    Infiltration 15,296
    Walls 19,746
    People 0
    Windows 3,588
    Misc 0
    Ceilings 2,291
    Floors 5,678
    Doors 1,120
    Skylights 0
    Glassdoors 0
    Fireplaces 4,370
    Duct 0

    Whole House 52,089

    So by adding 20% safety factor I get 62506 BTU. If a 96% efficiency 60000BTU furnace output is going to be 57600 BTU (right?) should I consider a 70000 BTU furnace or 60000BTU will be good enough? If 70000, will it be noisy considering the ducts are not big enough (as somebody told me)?

    Thanks.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,750
    I wouldn't add a 20% safety.

    60,000 should be plenty.
    Yes, a 70,000 could be loud with under sized ducts.
    A 70,000BTu 95% would need 1026CFM for a temp rise of 60 across the heat exchanger.
    A 60,000 BTU 95%, only needs 879 CFM for the same 60 rise.

    That air flow difference can make your ducts system louder.
    Or, the ducts could be small enough, that the furnace can't move enough air. And the furnace rides, or trips the high limit. Which would cause high heating bills.
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  9. #9
    Join Date
    Jul 2007
    Location
    Beautiful, Philadelphia, the City of Brotherly Love!
    Posts
    1,089
    Go one step better for the furnace, install a two stage unit. This way if you choose a 70k btu, it will mostly run on low fire. Personally I would not add 20% factor, just guess low on items you are not sure about. Usually I like to size condensing furnaces as close to the heat loss as possible. I find most folks tighten up the house and add insulation which reduces the heat loss, making the furnace over-sized, if they start out with too much furnace input to begin with.

  10. #10
    Join Date
    Sep 2009
    Posts
    25
    Thanks for your replies.
    I have interviewed 8 contructors. The one that I feel most comfortable with sells Bryant Trane and Rheem. I like the features that come with 60000 BTU Bryant 355AAV and Evolution Thermostat. This was also the least expensive option between the 3. I was thinking about York YP9C but couldn't find a contructor that I can trust. Then I had a few contructors that offered Amana/Goodman but it only comes with 70000BTU which seems too much according to my load calc. So that leaves me with Bryant I guess.

  11. #11
    Join Date
    Apr 2002
    Posts
    11,808
    a 2x4 wall in Canada is R12

    most common furnaces I used to sell in T-Bay were 60 and 75K, -8F sounds pretty chilly for Toronto

    something built in the early 70s in T-Bay would be about 2000 sqaure feet including basement to have a 52000 heat loss

    I would pass on the two stage myself, will have good results with a single stage sized on the money.

    As beenthere has warned you, the newer furnaces will probably move about 50% more air than the older furnaces with a pilot light.

    If your old furnace has a pilot light, you should consider upgrading mechanical ventialtion now
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  12. #12
    Join Date
    Sep 2009
    Posts
    25
    Quote Originally Posted by Carnak View Post
    a 2x4 wall in Canada is R12

    most common furnaces I used to sell in T-Bay were 60 and 75K, -8F sounds pretty chilly for Toronto
    I was going by max temperature both ways. Last year we had a few weeks that were at about -8F. Should I put the average temperature instead?

    something built in the early 70s in T-Bay would be about 2000 sqaure feet including basement to have a 52000 heat loss

    I would pass on the two stage myself, will have good results with a single stage sized on the money.

    As beenthere has warned you, the newer furnaces will probably move about 50% more air than the older furnaces with a pilot light.
    The house was build in 1987. Is moving 50% more good or bad? Will a single stage furnace move less air?

    If your old furnace has a pilot light, you should consider upgrading mechanical ventialtion now
    Okay the more I hear from you guys the less I want to replace my working furncace at all . I was trying to get some more camfort, filter the dust with a newer cleaning system, reduce the noice and save some money on the bills. But really, reading on forums about all the troubles people got into with the new furnaces and understand how careless most of the contructors are made me think - may be I should wait until my old furnace reeeeeely breaks.

    Yes, my old furnace has a pilot light. What does it mean "upgrading mechanical ventilation" and how is it related to the pilot light?

    thanks.

  13. #13
    Join Date
    Apr 2002
    Posts
    11,808
    For houses OF is a typical outdoor design condition in TO area, for a commercial building they would use -3F.

    A new furnace will move more air, more air in same ducts means more noise

    When you have a pilot light you usually have what is called a drafthood, an opening that lets room air get drawn up the chimney with the products of combustion. When the furnace is off in the winter, as in inbetween heat calls, room air still goes in that draft hood and up the chimney.

    So in cold weather that chimney ventilates the home 24/7. A home always has the same amount of air in it, so when room air goes up that chimney, cold dry outside air will infiltrate in to replace it.

    Cold air holds little moisture so this tends to and keeps the home dry in the winter, even to the point of needing a humidifier.Get the old wives saying 'gas heat is dry heat' because of this.

    When you upgrade the furnace there is no longer a draft hood and you lose that 24/7 ventilation effect in the winter. It is not uncommon after upgrading a furnace (without a ventilation upgrade) that the house suddenly becomes too humid in the winter and you get a problem with condensation on your windows.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

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