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Old 02-25-2013, 12:27 PM   #106
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Will the size of my ducts have to be changed?


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Originally Posted by digitalplumber View Post
Thats interesting, I always assumnned that the purpose of a manual j was for it to ultimately tell YOU the total cfm necessary based on the numbers you entered?

So do you then look at the final Sensible and Latent cooling BTU's and compare these 2 to determine if your original unit size is correct??

Do you have to enter a number there?
Dp--I was just thinking about this when you posted it to me a while back.>>>>>>> But I have seen more and more where some experts have said that sometimes they need to re-evaluate the load calc and listen more to the customer. <<<<<<

I really enjoy the fact that they have an online program for homeowners to do their own load calcs but I have found I have to go over it with a fine tooth comb to hope that I come up with the right size unit for my house.
I am almost like a danger to myself being a green horn. I have no experience in doing this but it is all I can do short of hiring someone.

Anyway to get to my point I was reading FAQ and they talk about external shading and internal shading. Originally I took credit for windows/patio doors in my house and outside credit for how long the sun is hitting certain windows etc,...

The program says that on a beautiful summer day I would probably have all the blinds open so they said do not take credit for either external or internal shading. Leave both at 0%. After making the necessary changes (unchecking all the boxes) my total heat gain went from 20,874 BTUH to 24,911 BTUH

And the laugher is I live by myself and most of the time 80% of the blinds are going to be left closed in my house. But I do understand I am getting "worst case scenario" advice from the program.Now I have to decide what to do with that information. The good part is I understand it where if I hired someone to do the load calc for me I don't think it would register in my mind just looking at a finished load calc on paper.


The additional BTUHs just from eliminating external/internal shading has bumped me up to a 2 ton unit. But I learned that now I have the knowledge that my 2 ton at this point is plenty when the drapes/blades are closed and still the 2 ton unit will fight the good fight to keep things cool when all the blinds are open.
Not finished reading all the information on the load calc site yet. Not finished with the decision making on the load calc site yet. Still learning things.


Last edited by Pawl; 02-25-2013 at 01:10 PM.
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Old 02-25-2013, 03:35 PM   #107
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Will the size of my ducts have to be changed?


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Originally Posted by Pawl View Post
Dp--I was just thinking about this when you posted it to me a while back.>>>>>>> But I have seen more and more where some experts have said that sometimes they need to re-evaluate the load calc and listen more to the customer. <<<<<<

I really enjoy the fact that they have an online program for homeowners to do their own load calcs but I have found I have to go over it with a fine tooth comb to hope that I come up with the right size unit for my house.
I am almost like a danger to myself being a green horn. I have no experience in doing this but it is all I can do short of hiring someone.

Anyway to get to my point I was reading FAQ and they talk about external shading and internal shading. Originally I took credit for windows/patio doors in my house and outside credit for how long the sun is hitting certain windows etc,...

The program says that on a beautiful summer day I would probably have all the blinds open so they said do not take credit for either external or internal shading. Leave both at 0%. After making the necessary changes (unchecking all the boxes) my total heat gain went from 20,874 BTUH to 24,911 BTUH

And the laugher is I live by myself and most of the time 80% of the blinds are going to be left closed in my house. But I do understand I am getting "worst case scenario" advice from the program.Now I have to decide what to do with that information. The good part is I understand it where if I hired someone to do the load calc for me I don't think it would register in my mind just looking at a finished load calc on paper.


The additional BTUHs just from eliminating external/internal shading has bumped me up to a 2 ton unit. But I learned that now I have the knowledge that my 2 ton at this point is plenty when the drapes/blades are closed and still the 2 ton unit will fight the good fight to keep things cool when all the blinds are open.
Not finished reading all the information on the load calc site yet. Not finished with the decision making on the load calc site yet. Still learning things.

Check back in with us after all is said and done!
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Old 02-25-2013, 04:35 PM   #108
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Will the size of my ducts have to be changed?


Quote:
Originally Posted by digitalplumber View Post
Thats interesting, I always assumnned that the purpose of a manual j was for it to ultimately tell YOU the total cfm necessary based on the numbers you entered?

So do you then look at the final Sensible and Latent cooling BTU's and compare these 2 to determine if your original unit size is correct??

Do you have to enter a number there?
The program has no way of knowing the SHR of the equipment you are going to use. Nor does it decide that your going to use a heat pump instead of a gas furnace or vice versa. You could be using a gas furnace, which can't be gotten in the exact size your house needs. So you may be using the next size up. So you have to enter the CFM for both heating and cooling, and then size the duct for the one needing the most air.
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Old 02-26-2013, 07:33 AM   #109
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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 program has no way of knowing the SHR of the equipment you are going to use. Nor does it decide that your going to use a heat pump instead of a gas furnace or vice versa. You could be using a gas furnace, which can't be gotten in the exact size your house needs. So you may be using the next size up. So you have to enter the CFM for both heating and cooling, and then size the duct for the one needing the most air.

How can you know what equipment you are going to use if you dont know all of the other data and plug it into a manual j type program? That is what I always hear from you guys?

I'm really confused now????????
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Old 02-26-2013, 04:23 PM   #110
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Will the size of my ducts have to be changed?


Quote:
Originally Posted by digitalplumber View Post
How can you know what equipment you are going to use if you dont know all of the other data and plug it into a manual j type program? That is what I always hear from you guys?

I'm really confused now????????
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Your confused? Just when I think its starting to make sense?

With the load calculation program I clicked on the tools section at the top of the page and then clicked on CFM per room calculation, then I have to choose either one air handler for the whole house or one air handler for each zone. I chose one air handler for the whole house.
Then I have to enter "the CFM of the equipt chosen for this house" by the cfm numbers the program offers. I dont have an ac unit yet.
Anyway I think the range of cfm numbers offered by the program are based on the outside design temp (80)/ inside design temp (43) numbers because the range of cfm choices to choose from start at 500 cfm all the way up to 1100 cfm with 50 cfm increments (500,550.600, etc,.... up to 1100 cfm). It seems like this range of cfm increments is based on choosing 80 degrees earlier in Design Conditions.
But if I change from 80 degrees to 89 degrees under Outside Design conditions for Summer and leave the other 3 temperatures as they are the range of cfm increments to choose from change.
With 89 degrees selected they now go from 700 cfm (previously 500 cfm @80 degrees) to 1300 cfm (previously 1100 cfm @80 degrees) with not a big change in the overall cfm increase per room as you can see in the cooling and heating columns in the pictures I provided.

Outside Design
80 S -- 43 W
Inside Design
75 S -- 72 W

This is the only way I can start to understand what I am trying to do with not having any experience in this field is going over any reading material I can find many times and reading your feed back to help me see the whole picture and if I am on the right track.
I think from what I see on the cfm calculations paperwork here the duct size I will need for a 2 ton unit or 2.5 ton or 3 ton is not going to change a lot or at all because the amount of cfm increases doesnt seem to change the overall amounts of cfm needed for each room alot.
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Old 02-26-2013, 04:30 PM   #111
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Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Your confused? Just when I think its starting to make sense?

With the load calculation program I clicked on the tools section at the top of the page and then clicked on CFM per room calculation, then I have to choose either one air handler for the whole house or one air handler for each zone. I chose one air handler for the whole house.
Then I have to enter "the CFM of the equipt chosen for this house" by the cfm numbers the program offers. I dont have an ac unit yet.
Anyway I think the range of cfm numbers offered by the program are based on the outside design temp (80)/ inside design temp (43) numbers because the range of cfm choices to choose from start at 500 cfm all the way up to 1100 cfm with 50 cfm increments (500,550.600, etc,.... up to 1100 cfm). It seems like this range of cfm increments is based on choosing 80 degrees earlier in Design Conditions.
But if I change from 80 degrees to 89 degrees under Outside Design conditions for Summer and leave the other 3 temperatures as they are the range of cfm increments to choose from change.
With 89 degrees selected they now go from 700 cfm (previously 500 cfm @80 degrees) to 1300 cfm (previously 1100 cfm @80 degrees) with not a big change in the overall cfm increase per room as you can see in the cooling and heating columns in the pictures I provided.

Outside Design
80 S -- 43 W
Inside Design
75 S -- 72 W

This is the only way I can start to understand what I am trying to do with not having any experience in this field is going over any reading material I can find many times and reading your feed back to help me see the whole picture and if I am on the right track.
I think from what I see on the cfm calculations paperwork here the duct size I will need for a 2 ton unit or 2.5 ton or 3 ton is not going to change a lot or at all because the amount of cfm increases doesnt seem to change the overall amounts of cfm needed for each room alot.

But my point is, if you know the equipment you are installing???? why use this program???? This seems like it is backwards??? I know the pros are sitting back LTAO , but I am really confused now.

See I thought that this is what this program, everyone raves about needing, did for you. You enter all of the info you have about the home that it needs, then it spits out the BTUS for cooling and heating and you buy based on that.

BTW could you go to that web page I listed and enter some dat and see if it gets close to the program you are using?
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Old 02-26-2013, 05:32 PM   #112
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Will the size of my ducts have to be changed?


BTW could you go to that web page I listed and enter some dat and see if it gets close to the program you are using?[/QUOTE]

would you give me that site again? I am going to scroll back through your old posts and look for it again
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Old 02-26-2013, 06:10 PM   #113
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Will the size of my ducts have to be changed?


Quote:
Originally Posted by digitalplumber View Post
How can you know what equipment you are going to use if you dont know all of the other data and plug it into a manual j type program? That is what I always hear from you guys?

I'm really confused now????????
You need to choose equipment that can meet the sensible and latent loads the program list.

You can take 2-2 ton units, one from one manufacturer and another from a different manufacturer, and they won't have the same sensible and latent capacities. One may need its blower slowed down to get the latent a home needs. Or may need the blower sped up to get the sensible the house needs.

The program tells you what capacities, you have to select the equipment.
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Old 02-26-2013, 06:13 PM   #114
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Will the size of my ducts have to be changed?


Quote:
Originally Posted by Pawl View Post
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Your confused? Just when I think its starting to make sense?

With the load calculation program I clicked on the tools section at the top of the page and then clicked on CFM per room calculation, then I have to choose either one air handler for the whole house or one air handler for each zone. I chose one air handler for the whole house.
Then I have to enter "the CFM of the equipt chosen for this house" by the cfm numbers the program offers. I dont have an ac unit yet.
Anyway I think the range of cfm numbers offered by the program are based on the outside design temp (80)/ inside design temp (43) numbers because the range of cfm choices to choose from start at 500 cfm all the way up to 1100 cfm with 50 cfm increments (500,550.600, etc,.... up to 1100 cfm). It seems like this range of cfm increments is based on choosing 80 degrees earlier in Design Conditions.
But if I change from 80 degrees to 89 degrees under Outside Design conditions for Summer and leave the other 3 temperatures as they are the range of cfm increments to choose from change.
With 89 degrees selected they now go from 700 cfm (previously 500 cfm @80 degrees) to 1300 cfm (previously 1100 cfm @80 degrees) with not a big change in the overall cfm increase per room as you can see in the cooling and heating columns in the pictures I provided.

Outside Design
80 S -- 43 W
Inside Design
75 S -- 72 W

This is the only way I can start to understand what I am trying to do with not having any experience in this field is going over any reading material I can find many times and reading your feed back to help me see the whole picture and if I am on the right track.
I think from what I see on the cfm calculations paperwork here the duct size I will need for a 2 ton unit or 2.5 ton or 3 ton is not going to change a lot or at all because the amount of cfm increases doesnt seem to change the overall amounts of cfm needed for each room alot.
If you run a 3 ton A/c at only 800 CFM like you would for a 2 ton. You will end up with a frozen evap coil.

A 3 ton takes much larger duct then a 2 ton.
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Old 02-26-2013, 08:41 PM   #115
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Will the size of my ducts have to be changed?


http://www.loadcalc.net





Quote:
Originally Posted by Pawl View Post
BTW could you go to that web page I listed and enter some dat and see if it gets close to the program you are using?
would you give me that site again? I am going to scroll back through your old posts and look for it again[/QUOTE]
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Old 02-27-2013, 10:03 PM   #116
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Will the size of my ducts have to be changed?


I thought I had everything on my load calc but found a couple more things but hopefully this is the grand total but maybe not. I was reading through all the instructions from the program one more time and they mentioned if I get a low cooling load its because I might have done a couple of things they recommend not to do. The only one I did not do was eliminating all outside shading and inside window covers. They said calculate with inside windows not covered up.So I took them out and the total BTUH on Total Heat Gain went from 15,643 (1.5 tons) with shading,blinds,curtains,roll up shades included to 24,313 BTUH (2 tons) with shading,blinds,curtains,roll up shades NOT INCLUDED.
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Last edited by Pawl; 02-27-2013 at 10:30 PM.
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Old 02-27-2013, 10:06 PM   #117
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Will the size of my ducts have to be changed?


2nd copy
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Old 02-27-2013, 10:27 PM   #118
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Will the size of my ducts have to be changed?


I increased that outdoor Summer Temperature on the Manual J program to 86 degrees and it still showed I should use a 2 ton unit. When I increased it to 88 degrees it went to a 2.5 ton unit. I think 2 ton is looking like my choice. What do you think guys?

The Total Heat Loss is 37,849 BTUH. The program says to add 20% to that for a total of 45,419 BTUH. Do they round these amounts to 50,000?

My 1975 heating unit is rated at 100,000 BTUH (input) and 80,000 BTUH bonnet capacity. Of course the house had single pane windows,very little insulation from day one. The house was built in 1965 and this heater says 1975 on it. Maybe the original heater was rated lower and they purchased a larger one or maybe the original one took a dump. Maybe when they bought a new one they told them they wanted a larger one because the original one was not getting it done or the installer sold them a larger one.
My heater is over 30 plus years and it works okay but now I am going from a 100,000 BTUH / 80,000 bonnet capacity to a recommendation of 45,419 BTUH. Is that possible?
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Last edited by Pawl; 02-27-2013 at 10:53 PM.
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Old 02-27-2013, 10:29 PM   #119
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Will the size of my ducts have to be changed?


DP - I tried doing that load calc but I cant read the drop down window choices very well because I dont have right/latest internet explorer.
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Old 02-27-2013, 10:50 PM   #120
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Will the size of my ducts have to be changed?


Beenthere - They mention Arizona/Nevada in the program as an example of states located in a dry climate. I am just assuming California is included even though it is not mentioned. We dont have much humidity at all where I live. The program says latent gain is not included in a dry climate so when I am shopping that whatever unit I get is going to be based entirely on sensible gain. Correct?

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