# Determining A/C size

Originally Posted By: egriffin
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I was looking at a fairly new Carrier A/C, but couldn’t find any indication of the size. Couldn’t find BTU, W or kw, or tons. Is there any particular way to determine size. It did have model and serial numbers.

Originally Posted By: tshields
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Divide the first two numbers after a letter in the sn# by 12. For example…

3j30kls4, 30 divided by 12 is 2.5 tons

Originally Posted By: Blaine Wiley
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On a carrier unit the tonnage is in the model number. I.E. 38Q042300 is a 3? ton unit (042 is 42000 BTU, 12000 BTU per A/C ton). That is actually true on any BDP unit.

Most manufacturers have the tonnage in the model number.

Originally Posted By: Vince Santos
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On Bryant it’s also the model number:

565BJ036 = 3ton

--
Desire is half of life, indifference is half of death.
--Kahlil Gibran

Originally Posted By: jpeck
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Except when you get to Carrier air handlers.

Now that becomes a problem. The 002 air handler can be used with many sizes of condenser units - talked to the factory just last week on this.

Carrier used to give the size in the air handler model number, then they changed the coding.

001
002
003
004
005
006

I was told that 001 was 1 1/2 ton. That 002 was 2 ton. That 003 was 2 1/2 ton. That 004 was 3 ton. That 004 was 3 1/2 ton. That 005 was 4 ton. That 006 was 5 ton. Yep, they said no 4 1/2 ton.

Then I call next week to clarify that I was told right. And find out I was told wrong.

The 002 can be used with condenser units from 2 ton to 4 ton, depending on various other things the a/c contractor is trying to accomplish. But the 003 can be used from 2 ton to 4 ton too.

I stopped asking as it really did not matter any more. I was told that the only way to know was to call the a/c company which installed the units and have them explain their sizing choice to me. That is not going to happen.

--
Jerry Peck
South Florida

Originally Posted By: Vince Santos
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Waayyy to much trouble in my opinion. I guess that would get an “unable to determine size” in my report. Of course it’s always nice to be able to go the extra mile for your client. I believe they would appreciate the effort. And of course a satified customer equates to more business.

Desire is half of life, indifference is half of death.

–Kahlil Gibran

Originally Posted By: roconnor
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Keep in mind that Jerry is talking about the air handler size. The compressor size, which is more important, should still be easy to determine from the model number …

Robert O’Connor, PE

Eagle Engineering ?

Eagle Eye Inspections ?

NACHI Education Committee

I am absolutely amazed sometimes by how much thought goes into doing things wrong

Originally Posted By: ekartal
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You can also divide the RLA rating by 7.

Erol Kartal

Originally Posted By: Vince Santos
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This may not be enough information but here is my question. I was wondering what the size of this unit would be?

Model # TTP048C100A3

Serial # K421KU9FF

I am thinking it is a 3.5 or 4 ton unit..
My next question is do you think this is oversized for a 2600 sq. foot home ??

--
Desire is half of life, indifference is half of death.
--Kahlil Gibran

Originally Posted By: jpeck
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Vince,

Model # TTP048C100A3

4 ton.

Most places, the rule of thumb is 500-600 sf per ton. That would put a 4 ton unit on the small side of 'OK' to 'too small'. Probably too small.

Down here, way too small. Down here, that should have 5-6 tons of a/c.

--
Jerry Peck
South Florida

Originally Posted By: roconnor
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Is that 2,600 s.f. of finished/conditioned space? If so it does appear to be undersized and evaluation by an AC specialist would be advised.

Robert O’Connor, PE

Eagle Engineering ?

Eagle Eye Inspections ?

NACHI Education Committee

I am absolutely amazed sometimes by how much thought goes into doing things wrong

Originally Posted By: dbowers
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Vince -

I'm in Kansas City and a 4 Ton A/C unit would be more than adequate for the average 2,600 sf house and you're in a cooler climate than I - BUT the only way to really know what is needed is to do have a competent HVAC contractor do a heat loss analysis on the home.

That requires doing things like knowing how many windows; which way does the house face; how much insulation; etc, etc. Its not a hard calculation for someone that knows how to do it - however, it can take an hour or two to do it properly.

The old rules of thimb on so much tonage per so many square feet are just that - rough guesstimates. In a hotter climate like Texas, Florida, etc the number will be lower - in a cooler climate they will be higher.

Originally Posted By: Vince Santos
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I think I should stop telling my client the size of the unit unless it’s very undersized of oversized. I don’t even know why I mentioned it during my last two inspections. On one of them my client called me a couple days later and said, “the only thing you left out of the report is if you think the unit is too large.” I made the mistake of saying out loud to him that it may be to big. From now on I will just get the numbers, determine the size and leave it at that. Unless like I said, it’s way to small or too big.

As I understand it, heat load calculations are out of the scope of a normal home inspection.

One thing I have been coming across a lot is my clients asking me how they should fix things. There are some things I think I do know how to fix as it seems obvious. For example, I saw chimney flashing the other day that was a wrong and I told my client how it should be done. Do you guys ever say how things should be fixed or just refer them to a licensed builder etc. and leave it at that?

--
Desire is half of life, indifference is half of death.
--Kahlil Gibran

Originally Posted By: Blaine Wiley
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I don’t give repair recommendations, but I’m sure there are many inspectors who do. I’ve been out of construction for quite a while, so there may just be a better way to do something that I haven’t kept up with!

I also just follow the basic HI guideline. Observe and report.

Originally Posted By: kmcmahon
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AS HI’s doing calcs to determine size is beyond our scope. Not that it’s bad, but it is beyond our scope and you better be sure of your calculations or you’ll be liable.

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