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  1. #14
    Join Date
    Dec 2010
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    The Quad-Cities area (midwest).
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    Quote Originally Posted by rapida View Post
    Sorry for my ignorance, George2. Is each 6" supply 100 cfm max? Or with a bigger furnace and fewer supplies, each 6" supply can provide more than 100 cfm?

    I didn't understand what you meant by "tapping" into the existing living room supplies. Does it mean drawing 6" supplies directly from the 16"x8" without extending the length of the 16"x8" duct? If so, that was one of the contractors suggested to do. He didn't want to extend the 16"x8" duct because it will "increase too much air space for the furnace to handle". Was it a valid point?

    A mini-split system is a great idea as mentioned, but because you said you don't have the space or desire to go that route, I'll continue with our conversation on the ductwork.

    Adding extra 16"x8" will not effect the airflow anymore than the extra lengths of 6" that would be required if the main duct was not extended. It just depends on the lay-out. A 6" pipe will deliver about 120 cfm at .1 static pressure. Length of the duct and supplies will be a factor as well as the number of supplies. I use a round number of 100 cfm of airflow for a 6" pipe. This is a number I use to size the ductwork in my head. Using your house as an example, with the 8 - 6" supplies, I would size the duct to 18"x8". You want to add 3 more, the duct should start at 24"x8". We used to size the supplies (5", 6" or 7") according to the room size, but the cost of all the different materials (sizes) just became to costly.

    When you mentioned "tapping", what I have seen is contractors do is to put a tee on a existing supply and then extend to the addition from that point. This doesn't work well. It was a misunderstanding on my part....sorry.

  2. #15
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    Quote Originally Posted by rapida View Post
    On either coast or anywhere USDA zone 6 or above I'll just go with a mini-split. The problem is, in MN (zone 4) a mini-split is only half the solution because the heat pump will stop working before outside temp drops below 0F. That's 1-2 months here. If I have to supplement with baseboard heat I might just do the baseboards without any AC. Here AC is far less important than heat.

    None of the contractors did a load calc. Can I do it myself?

    I can't even find the blower capacity for the Carrier ICS 58MVC on the Carrier web site. Where else can I find that info?
    The blower size will be in the model number as a 42, 48 or 60. You have a ECM blower motor which is a good thing.

  3. #16
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Blower size on a carrier week be so getting like a 12, 14, 16, 20 at the end of the model number. The is the nominal capacity in hundreds of cfm. So a - 14 can support up to a 3.5 ton, a 12, 3 tons or 1200cfm. Carrier runs lower airflow on their systems.

    Sent from my SGPT12 using Tapatalk 2

  4. #17
    Join Date
    Mar 2013
    Posts
    16
    George2 and motoguy128, thanks for your input.

    The furnace model # is 58MVC080-F-10114. Is the blower size 14 and furnace 80,000 BTU?

    I did a load calculator using the tool at http://www.loadcalc.net/load.php. I got the heating load at 5,000 BTU and cooling load at 1,800 BTU for the sun room. Does it make sense? I had trouble putting in the info for the whole house, and kept getting 70,000 BTU for heating and 30,000 BTU for cooling the whole house. I am not sure whether this is right. Let's say if the 70,000 BTU is correct:

    80,000 BTU x 95% AFUE = 76,000 BTU
    70,000 BTU (house) + 5000 BTU (sun room) = 75,000 BTU

    So it's almost perfect match? Did I make any mistakes? If the load calculation for the house is wrong and I need over 71,000 BTU for the house alone, am I going to damage the furnace by adding another 5,000 BTU load from the sun room?

  5. #18
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    2,630
    Quote Originally Posted by rapida View Post
    George2 and motoguy128, thanks for your input.

    The furnace model # is 58MVC080-F-10114. Is the blower size 14 and furnace 80,000 BTU?

    I did a load calculator using the tool at http://www.loadcalc.net/load.php. I got the heating load at 5,000 BTU and cooling load at 1,800 BTU for the sun room. Does it make sense? I had trouble putting in the info for the whole house, and kept getting 70,000 BTU for heating and 30,000 BTU for cooling the whole house. I am not sure whether this is right. Let's say if the 70,000 BTU is correct:

    80,000 BTU x 95% AFUE = 76,000 BTU
    70,000 BTU (house) + 5000 BTU (sun room) = 75,000 BTU

    So it's almost perfect match? Did I make any mistakes? If the load calculation for the house is wrong and I need over 71,000 BTU for the house alone, am I going to damage the furnace by adding another 5,000 BTU load from the sun room?
    The blower number is missing........it's probably a 3.5 ton blower on the 80,000 but furnace. More than enough blower.

  6. #19
    Join Date
    Jul 2005
    Posts
    5,491
    Quote Originally Posted by rapida View Post
    George2 and motoguy128, thanks for your input.

    The furnace model # is 58MVC080-F-10114. Is the blower size 14 and furnace 80,000 BTU?
    Yes and yes.

    14 = 1400 cfm max.
    80 = 80,000 btu input rate (approximate)

    And yes to your previous question. The cfm through a 6" duct will depend upon the pressure drop across it and upon it's equivalent length.

  7. #20
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,630
    Quote Originally Posted by hvacrmedic View Post
    Yes and yes.

    14 = 1400 cfm max.
    80 = 80,000 btu input rate (approximate)

    And yes to your previous question. The cfm through a 6" duct will depend upon the pressure drop across it and upon it's equivalent length.
    I didn't even notice the numbers at the end. They have changed the model #s since I've sold Carrier. The condensed model # used to be: 58MVC042080. 42 (3.5 ton) was the blower size.

  8. #21
    Join Date
    Mar 2013
    Posts
    16
    How many cfm is it if the blower size is 42? Is it 1400 cfm or 4200 cfm?

  9. #22
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    Quote Originally Posted by rapida View Post
    How many cfm is it if the blower size is 42? Is it 1400 cfm or 4200 cfm?
    1,400 equals 3.5 tons. 400 cfm per ton

  10. #23
    Join Date
    Mar 2013
    Posts
    16
    Thanks again George2. But isn't 1,400 cfm too small for my house? I thought I need 1 cfm per sqft, and that's 4,400 cfm. If I go by 6" supplies at 100 cfm each, with 14 registers up and 9 registers down, I will need 2,500 cfm. Did I miss something? Why they don't match?

  11. #24
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    2,630
    Quote Originally Posted by rapida View Post
    Thanks again George2. But isn't 1,400 cfm too small for my house? I thought I need 1 cfm per sqft, and that's 4,400 cfm. If I go by 6" supplies at 100 cfm each, with 14 registers up and 9 registers down, I will need 2,500 cfm. Did I miss something? Why they don't match?
    We typically size the blower to the A/C needed. We try not to oversize the blower because of the air noise that can occur and the effect on the A/C. Your blower speed is set to the size of the A/C. Let's assume your A/C is a 3 ton. The blower is set to that 1,200 cfm setting for the A/C requirements. That will be the most air your furnace is moving. In the furnace mode, you're moving less air than that. You can change the blower speed to a higher setting in the continuous fan mode.

    With all the blower setting now available, noise, if the ductwork is correct, is not an issue. In other words, that furnace comes with a optional 5 ton blower (2,000 cfm). Under normal situations, a homeowner would not have a need for all that extra "power". But with the ECM motor and all the CFM settings available, that 5 ton blower even works with a 3 ton A/C. If said furnace had a PSC motor, that wouldn't be efficient.

    Your thinking is correct regarding the supplies verses the cfms available, but that is where balancing the airflow comes in. That is why I like zoning so much. It automatically increases the airflow (heating or cooling) to a particular area when the other zones are satisfied.
    Last edited by George2; 03-31-2013 at 06:23 AM. Reason: spelling

  12. #25
    Join Date
    Mar 2013
    Posts
    16
    Quote Originally Posted by George2 View Post
    We typically size the blower to the A/C needed. We try not to oversize the blower because of the air noise that can occur and the effect on the A/C. Your blower speed is set to the size of the A/C. Let's assume your A/C is a 3 ton. The blower is set to that 1,200 cfm setting for the A/C requirements. That will be the most air your furnace is moving. In the furnace mode, you're moving less air than that. You can change the blower speed to a higher setting in the continuous fan mode.
    Does it mean after I extend the duck work, if I have any problem with the temperatures not balanced, I can change the blower speed to high to reduce the temperature difference in the house?

    Quote Originally Posted by George2 View Post
    With all the blower setting now available, noise, if the ductwork is correct, is not an issue. In other words, that furnace comes with a optional 5 ton blower (2,000 cfm). Under normal situations, a homeowner would not have a need for all that extra "power". But with the ECM motor and all the CFM settings available, that 5 ton blower even works with a 3 ton A/C. If said furnace had a PSC motor, that wouldn't be efficient.

    Your thinking is correct regarding the supplies verses the cfms available, but that is where balancing the airflow comes in. That is why I like zoning so much. It automatically increases the airflow (heating or cooling) to a particular area when the other zones are satisfied.
    I thought zoning would help too. But those ICS thermostats are so expensive. George2, do you think I can first try without zoning, and if the comfort level in the sun room or house is not as desired, then add zoning?

    Does my plan sound good:
    1. extend the trunk line and reduce the size of the extended part to 6"x8" (so that the air to the living room is not "robbed" as much)
    2. add 3 supplies to the sun room from the extended trunk
    3. if temperature cannot reach desired level, add cold air return to the sun room
    4. if it still doesn't work, add zones (do I have to have 3 zones since I have 3 branches, or can I just zone the 2 branches for the main level?)

  13. #26
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,481
    Sun rooms by their design are horribly hard to keep comfortable. Aside from a seperate "mini-split" you'll probably not be happy with the results however as it sounds like you want to take the cheapest approach...uh....forget something that will really work. Just let the existing system try and keep up with this addition and assume you'll not be happy with the comfort level. I remember we had a customer who built a large sun room/entertainment room onto his house. I figured the loss/gain and installed a SEPERATE 3 1/2 ton heat pump for this sun room alone. It was a beautiful addition, and they were very pleased (and use the room a lot to entertain!). Do it the cheapest way possible and you'll probably not be happy.

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