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Help Sizing Carrier AC

Posted by pvansh (My Page) on
Wed, Apr 2, 14 at 22:13

Hi Folks,

First time poster here. I recently moved into a brand new 2-storey home in the suburbs of Toronto. The home is 4300sqft (not including basement). The basement is unfinished. We have 10ft ceilings on the main floor, 9ft on the 2nd floor. We also have a Vanee 60H HRV.

I have the following Carrier Comfort Series furnace installed in the house -- 59sc5a100s21-14. Based on my research, this is a 100k BTU furnace that has a 1400cfm blower (max cooling is 1545 cfm according to the manual).

My builder did a heat load calculation as part of the building permit. That calculation calls for a 3.56 ton AC. I have heard very mixed reviews from HVAC contractors here, ranging from 3.5T to 5T. It is clear that I cannot go ahead with a 5T (oversized, blower too weak), but I need some advice on where to end up between 3.5T and 4T. From my reading on this forum, it appears that 350cfm/ton is acceptable for Carrier. That would lead me to believe that I should be good with 4T, however some HVAC contractors have indicated I need AT LEAST 400cfm/ton to avoid freezing of the coil.

I am planning on purchasing the Carrier Infinity 24ANB6 AC.

I would greatly appreciate any expert advice on how to approach this. As I've said, I've heard mixed opinions from the HVAC contractors I've contacted thus far.

Thanks in advance!

Follow-Up Postings:

RE: Help Sizing Carrier AC

What are typical summer temps?

The furnace you have is low end builder grade 95% efficiency. It appears it has a conventional blower motor. This should be verified. If correct, you can not pair a high eff AC condenser like the Infinity with this furnace. You would be limited to a good basic sgl stage 13 SEER AC condenser with matching coil.

Probably not what you want to hear.

The blower motor rating/size on your furnace should be verified. It may have a higher rating than you think for AC cooling.


This post was edited by tigerdunes on Thu, Apr 3, 14 at 9:44

RE: Help Sizing Carrier AC

Thanks for the response. Our temps can get as high as 35-40 degrees Celsius with lots of humidity.

According to the Carrier manual, this is a single stage furnace with blower CFMs upto 1545. According to the manual it say it can cool 4-4.5T, however I am concerned whether this is achievable if static pressure is an issue.

Here is the manual for reference. I have the 100-14 :


RE: Help Sizing Carrier AC

Sounds like the furnace can handle the 4 ton condenser but that you are concerned your ductwork can not?

We lived in Rochester for 5 years and used the A/C for about 1 month per year. Given the short cooling season, I'd get the comfort or performance single stage outdoor condenser to match your indoor furnace.

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