# Thread: Help choosing correct size

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## Help choosing correct size

We are in our first house and need to replace the existing a/c unit (a 20 yr old 2.5 ton Lennox, original from the build). Our home is located in Ottawa, Ontario, Canada, is 1700 square feet, all new windows, a fair amount of shade, and we have rather humid summers. Attic is R30, walls are siding with brick in the front and R19.

We've had 4 guys in for quotes and they are equally split on whether we need a 2 ton or a 2.5 ton unit.

Both Lennox (XC14) guys said 2.5 tons, and went only by eyeballing the square footage and that is house is 2 storeys.

The Bryant (116B) and Trane (XR15) guys said 2 tons would be sufficient since we don't have a ton of windows and only get sun on one side of the house (west), which is half shaded by trees.

We're afraid if we go with the 2.5 ton it might be oversized and not dehumidify properly. What should we do?

Many thanks

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[QUOTE=Clover1;15668551]

Our home is located in Ottawa, Ontario, Canada, is 1700 square feet, all new windows, a fair amount of shade, and we have rather humid summers.
Attic is R30, walls are siding with brick in the front and R19.

The Bryant (116B) and Trane (XR15) guys said 2 tons would be sufficient since we don't have a ton of windows and only get sun on one side of the house (west),
which is half shaded by trees.

We're afraid if we go with the 2.5 ton it might be oversized and not dehumidify properly.
What should we do? [/QUOTE]

1. Tell me How many windows on each side of house
N 1
S 2
E 3
W 4
__18 square feet each

2. U-value & S.H.G.C. of the new windows
Solar heat Gain Coefficient - guess 0.5

3. Ceiling R-30
4. Wall R-19
5. 850 Square Foot each floor
6. Summer design Temp - ASHRAE 1% ~84'F, 0.4% ~87'F [20'C = 68'F, 25'C= 77'F, 30'C = 86'F]
7. T'stat set 74'F
8. Other than that, I'll have to guess Semi-Loose for a 20 year old house.

http://www.climate-zone.com/climate/...tl-airport.htm

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Originally Posted by dan sw fl

1. Tell me How many windows on each side of house
N 1
S 2
E 3
W 4
__18 square feet each

2. U-value & S.H.G.C. of the new windows
Solar heat Gain Coefficient - guess 0.5

3. Ceiling R-30
4. Wall R-19
5. 850 Square Foot each floor
6. Summer design Temp - ASHRAE 1% ~84'F, 0.4% ~87'F [20'C = 68'F, 25'C= 77'F, 30'C = 86'F]
7. T'stat set 74'F
8. Other than that, I'll have to guess Semi-Loose for a 20 year old house.

http://www.climate-zone.com/climate/...tl-airport.htm
Windows are:

N- 2
S- 2
E- 3
W- 5 (3 shaded by trees)

I found that url you listed in an earlier thread and tried it before posting this, but honestly after the first page my brain went numb. I'm not very good with numbers!

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## SMALLER The Better ...

Originally Posted by Clover1
We are in our first house and
need to replace the existing a/c unit (a 20 yr old 2.5 ton Lennox, original from the build).

Our home is located in Ottawa, Ontario, Canada,
is 1700 square feet,
all new windows,
a fair amount of shade, and we have rather humid summers.
Attic is R30, walls are siding with brick in the front and R19.

What should we do?
SENSIBLE HEAT GAIN < 14,000 BTU/HR ... 2-Ton is MORE Than Adequate

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## S M A L L

Originally Posted by Clover1
Windows are:
N- 2 S- 2
E- 3 W- 5 (3 shaded by trees)

I found that you listed in an earlier thread and tried it before posting this,
but honestly after the first page my brain went numb.
I'm not very good with numbers!
___ 2 TONS ... KISS .... KEEP IT SIMPLE & SINCERE

Total # of windows: 12
Sensible 15,300
Latent _ 3,860
Total __ 19,160 BTU/HR

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Originally Posted by dan sw fl
___ 2 TONS ... KISS .... KEEP IT SIMPLE & SINCERE

Total # of windows: 12
Sensible 15,300
Latent _ 3,860
Total __ 19,160 BTU/HR

Thanks

I tried opening your attached pdf's, but get an error message: "Clover1, you do not have permission to access this page. This could be due to one of several reasons:
Your user account may not have sufficient privileges to access this page. Are you trying to edit someone else's post, access administrative features or some other privileged system?
If you are trying to post, the administrator may have disabled your account, or it may be awaiting activation."

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Originally Posted by Clover1
Thanks

I tried opening your attached pdf's, but get an error message:
Send me an email and I'll reply with attachment.

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This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

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Last edited by jpsmith1cm; 04-30-2013 at 05:26 AM. Reason: non AOP Pro Member

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Originally Posted by mickeykool
I had this issue too. I think it happens for those that have few posts. Just log out and view the post and you will be able to download the attachment. Worked for me.
Thank you, that worked!

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mickeykool

This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

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Originally Posted by mickeykool
This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

You can find the rules for posting and qualifications here.
THAT'S IRONIC.

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We decided today to go with the company that installs Bryant, they were one of the two that recommended a 2 ton unit, and they have a better payment plan. My husband was concerned with the 76dB rating, but they'll be installing it on an a/c pad rather than brackets which should help a bit.

At any rate, it should be quieter than the 20 year old unit!

Thanks guys

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This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

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Last edited by jpsmith1cm; 05-01-2013 at 05:46 AM. Reason: non AOP Pro member

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