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Old 02-21-2013, 07:34 AM   #61
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Will the size of my ducts have to be changed?


What kind of furnace/heat are you putting in: Electric, Gas or a heat pump with backup strips?

Tons, per se, relates to AC size and BTU's relates to heat. Heat (Gas and Electric) usually requires less cfm to a room, versus AC cfm. I believe and will be corrected, that a heat pump uses same cfm for heat and cool mode.

So your outside AC condensor is rated at 2 tons and your furnace/blower is rated at a number from the manual j, just say 80,000 BTU for heat (80 or 90% efficiency) and will have a fan speed adjustment for the AC size. (As BT has stated above will need to be adjusted.)

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Old 02-21-2013, 08:57 PM   #62
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Will the size of my ducts have to be changed?


Is cfm measured by the amount of pressure coming out of each supply register?
My old heater (1975) uses natural gas and is rated at 100,000 BTUH with a bonnet capacity of 80,000 BTUH. I dont know how much calculating went into homes back in 1975.

Last edited by Pawl; 02-21-2013 at 09:01 PM.
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Old 02-21-2013, 09:42 PM   #63
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Will the size of my ducts have to be changed?


I found some weather data for my area where the point of meaurement was 2.5 miles away. I was hoping HVAC people I find can use this in figuring out correct tonnage. Maybe you guys can take these numbers and give me some insight. Is 6 years far enough to go back to get some useful averages?

Days over 89 degrees during each year below:

2007 - (5 days) 91 degrees 2x, 95 degrees 1x, 96 degrees 1x, 97 degrees 1x
2008 - (20 days) 90 degrees 4x, 91 3x, 92 1x, 93 3x,94 2x, 95 4x, 97 1x, 99 1x, 100 1x
2009 - (18 days) 90 degrees 3x, 91 1x, 92 3x, 93 5x, 94 2x, 96 1x, 97 1x, 99 1x, 102 1x
2010 - (14 days) 90 degrees 1x, 91 1x, 92 4x, 93 1x, 94 1x, 95 2x, 96 1x, 98 1x, 103 1x, 109 1x
2011 - (9 days) 91 degrees 4x, 92 3x, 94 1x, 100 1x
2012 - (16 days) 90 degrees 2x, 91 1x, 92 3x, 93 3x, 94 2x, 96 2x, 99 2x, 102 1x
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
89 degree days during each year below:

2007 - 6 days
2008 - 5 days
2009 - 4 days
2010 - 1 day
2011 - 3 days
2012 - 5 days

88 degree days during each year below:

2007 - zero
2008 - 2 days
2009 - 1 day
2010 - 3 days
2011 - 3 days
2012 - 10 days

87 degree days during each year below:

2007 - 4 days
2008 - 9
2009 - 1
2010 - 3
2011 - 2
2012 - 6

86 degree days during each year below:

2007 - 10 days
2008 - 11
2009 - 7
2010 - 4
2011 - 4
2012 - 6

85 degree days during each year below:

2007 - zero days
2008 - 3
2009 - 1
2010 - 1
2011 - zero
2012 - 7

84 degree days during each year below:

2007 - 10 days
2008 - 5
2009 - 3
2010 - 3
2011 - 6
2012 - 8

83 degree days during each year below:

2007 - zero days
2008 - 4
2009 - 5
2010 - 4
2011 - 3
2012 - 8

82 degree days during each year below:

2007 - 10 days
2008 - 15
2009 - 11
2010 - 6
2011 - 8
2012 - 6

81 degree days during each year below:

2007 - zero days
2008 - 3
2009 - 12
2010 - 3
2011 - 6
2012 - 10

80 degree days during each year below:

2007 - 9 days
2008 - 11
2009 - 15
2010 - 3
2011 - 4
2012 - 4

Last edited by Pawl; 02-22-2013 at 03:49 AM.
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Old 02-22-2013, 03:17 AM   #64
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Will the size of my ducts have to be changed?


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Originally Posted by digitalplumber View Post
Will a 1.5 work, dont know sounds like my scenario with the 3 ton. It worked mostly, but would run a very long time on the hot days and just be ok. If that bothers you, then I suggest you go to 2 tons and make sure you can be comfortable on the extreme days.

REMEMBER i am speaking to you as a homeowner to another homeowner, I am not an expert.
As one homeowner to another my issue here is I have never had air conditioning in my house using ducts so I have nothing to compare it too. I just had the smaller/larger window units,box fans,and ceiling fans, I have a much better understanding of what I am looking for after reading everything on this site. That is why I thought I would try to find the weather pattern for where I live and see if that would help add to a more informed decision.

When it comes to leaning one way or the other on tonnage meaning if I have a choice to go up a half a ton after compiling all the information I might hold firm. After doing all this research my house is starting to remind me of that statement that people always make when they say your house is always cold.
Since 1989 I was a single dad with 3 daughters playing sports,girl scouts,homework and we were always on the go. As funny as this sounds I did not consciously notice on a daily basis how my house felt at different times of the year by whatever was going on.Too busy raising kids all the time. I was always on my feet doing something so some of the tendencies of this house are only being noticed now because I have the time but mostly because I am putting in air conditioning and its part of solving the what size do I need question.
I am noticing that my house seems to stay relatively cool now with the way it faces west,dbl pane windows, 3' deep eaves all around the house up and down insulation,only one window upstairs that gets full sun all day,the rest get 4-6 hrs of sun,I live alone most of the time, I am going to have a new unit with new ducts that are totally sealed and insulated and there are other things I can still do to seal up my house some more from air leaks. I will also have enough information in hand to show an HVAC installer that I have done my homework.
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Old 02-22-2013, 03:45 AM   #65
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Will the size of my ducts have to be changed?


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Originally Posted by beenthere View Post
The summer design temp is the 97 1/2% temp. meaning only 2.5% of the time in a normal summer will the temp get above the design temp.

Not sure how many years the design temp is calculated from.
On my current Manual J Calculations under "Design Conditions" I set the Outdoor Summer temperature at 89 degrees:

Days over 89 degrees during the 365 day year in my weather data research for my city:

2007 - 5 days = 1.4%
2008 - 20 days = 5.5%
2009 - 18 days = 4.9%
2010 - 14 days = 3.8%
2011 - 9 days = 2.5%
2012 - 16 days = 4.4%

Have I got this right?
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Old 02-22-2013, 03:55 AM   #66
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Will the size of my ducts have to be changed?


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Originally Posted by digitalplumber View Post
What kind of furnace/heat are you putting in: Electric, Gas or a heat pump with backup strips?

I assume I will be using a gas heater.

So your outside AC condensor is rated at 2 tons and your furnace/blower is rated at a number from the manual j, just say 80,000 BTU for heat (80 or 90% efficiency) and will have a fan speed adjustment for the AC size. (As BT has stated above will need to be adjusted.)
Looking at my Manual J calcs I posted on here what size heater unit would my house require?
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Old 02-22-2013, 05:35 AM   #67
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Will the size of my ducts have to be changed?


You don't have that many days over 89, that are much above 89. The tonnage an A/C is rated to have is done at 80įF indoor temp, and 95įF outdoor temp. So a 2 ton will barely meet your load on the hottest days, and may lose ground a little, but not much. if you want to be able to maintain 75 to 70 on the hottest days, you would need a 2.5 ton.
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Old 02-22-2013, 08:45 AM   #68
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Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
Is cfm measured by the amount of pressure coming out of each supply register?
My old heater (1975) uses natural gas and is rated at 100,000 BTUH with a bonnet capacity of 80,000 BTUH. I dont know how much calculating went into homes back in 1975.

Your manual j will determine each rooms cfm. then you have to try and match duct size for that requirement.
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Old 02-22-2013, 09:01 AM   #69
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Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
Looking at my Manual J calcs I posted on here what size heater unit would my house require?
looks like 40,000 btu?????
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Old 02-22-2013, 09:03 AM   #70
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Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
Looking at my Manual J calcs I posted on here what size heater unit would my house require?

the manual j i have from my home lists that information for each room, yours does not apparently.
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Old 02-22-2013, 04:16 PM   #71
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Will the size of my ducts have to be changed?


So, I also researched the Winter temperatures in my area.The point of measurement was 2.5 miles away from my house. Any thoughts on what I will need in the way of heating.

Days under 38 degrees during each year below:

2007 - ( 6 days under 38 degrees) 32 degrees 2x, 33 degrees 1x, 37 degrees 2x,
2008 - ( 10 days under 38 degrees) 34 degrees 1x, 35 degrees 2x, 36 degrees 2x, 37 degrees 5x,
2009 - ( 7 days under 38 degrees) 35 degrees 2x, 36 degrees 2x, 37 degrees 3x,
2010 - ( 5 days under 38 degrees) 33 degrees 2x, 36 degrees 1x, 37 degrees 2x,
2011 - ( 15 days under 38 degrees) 31 degrees 1x, 32 degrees 1x, 34 degrees 2x, 35 degrees 5x, 36 degrees 4x, 37 degrees 2x.
2012 - ( 11 days under 38 degrees) 33 degrees 1x, 35 degrees 3x, 36 degrees 2x, 37 degrees 5x,
2013 - ( 16 days under 38 degrees) 31 degrees 1x, 32 degrees 2x, 33 degrees 3x, 34 degrees 1x, 35 degrees 2x, 36 degrees 3x, 37 degrees 7x,
* the numbers seem to point out that in the last 3 years it is getting colder here
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
38 degree days during each year below:
2007 zero days
2008 - zero days
2009 - 3 days
2010 - 4 days
2011 - 2 days
2012 - 2 days
2013 - 5 days
39 degree days during each year below:
2007 - 8 days
2008 - 6 days
2009 - 4 day
2010 - 2 days
2011 - 16 days
2012 - 6 days
2013 - 3 days
40 degree days during each year below:
2007 - zero days
2008 - 1
2009 - 7
2010 - 5
2011 - 8
2012 - 3
2013 - 1
41 degree days during each year below:
2007 - 8
2008 - 5
2009 - 8
2010 - 11
2011 - 13
2012 - 12
2013 - 3
42 degree days during each year below:
2007 - 10
2008 - 9
2009 - 12
2010 - 11
2011 - 10
2012 - 5
2013 - 4
43 degree days during each year below:
2007 - zero
2008 - 3
2009 - 18
2010 - 12
2011 - 9
2012 - 15
2013 - 2
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Old 02-22-2013, 04:22 PM   #72
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Will the size of my ducts have to be changed?


Quote:
Originally Posted by digitalplumber View Post
the manual j i have from my home lists that information for each room, yours does not apparently.
The program I used for the manual J load calc has some different options for the information I can retrieve. Are you talking about the different items that are measured and inputted into the program for each room with that rooms measurements and square footage? Because I can post that information.

Last edited by Pawl; 02-22-2013 at 04:28 PM.
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Old 02-22-2013, 04:28 PM   #73
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Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
The program I used for the manual J load calc has some different options for the information I can retrieve. Are you talking about the different items that are measured and inputted into the program for each room with that rooms measurements and square footage?
Not sure as I do not have the program, but you need to know what that report says you need for each room, cfm, so that you can also determine duct size. I would assume that is in there somewhere based on all of the data you entered.

If that program has an expiration, I would print every possible report you can before it expires.
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Old 02-22-2013, 04:53 PM   #74
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Will the size of my ducts have to be changed?


This picture shows the existing heating supply register. Just for conversation I feel that the new supply register will have to be moved between this ceiling fan and the window you are looking at. I am just extending the supply ducting toward that window. Moving it will also create distance between supply and return.

That is the east side of my house which gets sun on this window from sunrise until about 11am. That is a small round recessed light in the picture. There are four in the ceiling.

The new return will be installed somewhere right above the entrance to this room in the ceiling. With it located in that spot it will put the return closer to the new AC unit area. The entrance to this room is at the end of the hallway. About 8' back down the hallway is the entrance to the original heater in the closet.

Is their an advantage to having the return ducts as close as possible to the AC unit? For example I would think in a bedroom you can mount these ceiling registers/vents anywhere you want but there is obviously a sweet spot for both which will be the most advantageous in performance.
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Old 02-22-2013, 05:00 PM   #75
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Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
This picture shows the existing heating supply register. Just for conversation I feel that the new supply register will have to be moved between this ceiling fan and the window you are looking at. I am just extending the supply ducting toward that window. Moving it will also create distance between supply and return.

That is the east side of my house which gets sun on this window from sunrise until about 11am. That is a small round recessed light in the picture. There are four in the ceiling.

The new return will be installed somewhere right above the entrance to this room in the ceiling. With it located in that spot it will put the return closer to the new AC unit area. The entrance to this room is at the end of the hallway. About 8' back down the hallway is the entrance to the original heater in the closet.

Is their an advantage to having the return ducts as close as possible to the AC unit? For example I would think in a bedroom you can mount these ceiling registers/vents anywhere you want but there is obviously a sweet spot for both which will be the most advantageous in performance.

Again, basing on what I have read. Your supply vents need to be over the windows as you have indicated. All rooms.

As far as the return air, across the room from them. A short path back to the return, I assume, is a great idea but maybe getting to worrysome to accomplish or not even a worry.. Remember, you are adding this to a room you did not have before so it has to help.

Hopefully the real experts will chime in soon.

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