Q&A on how to determine the rated cooling capacity of an air conditioner or heat pump that you need.

This article series explains exactly how to determine how big your air conditioner or heat pump needs to be, and how to estimate the actual rated cooling capacity of an air conditioning system by examining various data tags and components.

FAQs: Determine Air Conditioning or Heat Pump Equipment Capacity

These questions & answers about translating A/C or heat pump numbers into actual cooling capacity and about how to figure out how big your air conditioner or heat pump needs to be were posted originally at RATED COOLING CAPACITY - so you certainly will want to review that article.

On 2019-02-17 by (mod) - how to use the cooling rule of thumb to calculate BTUs needed from Square Feet

Josen:

From the article above

A simple rule of thumb for relatively cool climates such as the Northeastern United States: one ton per 400 sq .ft. (Commercial) or one ton per 500 to 1000 sq .ft. (Residential)

Or we estimate an air conditioning requirement of one ton per 400 to 800 sq .ft. for Space Pak Systems.

15..15 = 232.5 sq.ft.

Using the 1 ton of cooling needed in a "typical" US home per 400-800 sq.ft. guideline,

We divide the actual square feet by the two "guideline" numbers of 400 and 800 sq.ft. per ton of A/C needed.

232/400 = 0.58 tons or converting to BTUH, 0.58 x 12,000 BTUH per ton = 6960 or rounded to 7000 BTUH using the 400 sq.ft. or "most cooling load needed"

to

232/800 = 0.29 tons or converting to BTUH, 0.29 x 12,000 BTUH per ton = 3,480 or rounding to 4000 BTUH for the least amount of cooling needed.

Naturally what your room really needs varies depending on factors like

1. the amount of solar gain in your room- window size, area, location, and extent of direct sunlight

2. building insulation and air leakage and other heat sources

3. personal choice

On 2019-02-17 by Josen

My bed room is 15.5×15×12 feet in size. Please say the sufficient ac capacity for my room

On 2017-07-05 by (mod) - get BTU number from model number?

K

It would help to know the brand.

On 2017-07-05 by Kadar

compress model number zr-72kcctfd522 how to find btu kindly advice

On 2017-06-11 by (mod) - How much cooling capacity do I need for 330,000 cubic ft. Building. T

Lance

The article above gives some rules of thumb about determining the cooling capacity needed for a building, but frankly, no one can give a more specific design-grade answer to a question about a building of unknown location, climate, sun exposure, design, number of floors, insulation level, and similar features that would make a rule-of-thumb guesstimate into something more precise.

For that you'll need an onsite HVAC design engineer or consultant - for me to make guesses from here in Genoa would be wild arm-waving and a disservice.

On 2017-06-11 by lance

How much cooling capacity do I need for 330,000 cubic ft. Building. To maintain 20 to 23degrees C

On 2017-04-24 by (mod) -

Chiboy I'm sorry but I don't understand the question.

kg is kilograms, a measure of weight.

"gas" - probably you mean "refrigerant gas" or "refrigerant" that might be in liquid or gas form. That's about a 1-ton cooling capacity system.

The volume of gas or charging weight of refrigerant if starting in liquid form depends not just on the horsepower of the compressor but on the physical volume for storage of refrigerant in the system including in the compressor, in the refrigerant tubing, and in the receiver if your compressor unit uses a receiver. So there's not one single right answer.

But help is at hand. Take a look at the air conditioner or heat pump itself, at its data tag where the specific refrigerant type and charge will be given.

On 2017-04-24 by Chiboy

What is the actual kg of gas for 1.5hp

On 2016-11-12 y Anonymous

how to calculate capacity of air cooled heat exchanger

On 2015-12-21 by (mod) -

Rick

As long as the refrigerant metering devices are properly sized and working you probably won't see an operating problem.

But an oversized system can result in other disappointments including:

1. inadequate dehumidification in cooling mode - the air cools down too quickly, the unit shuts off, and moisture is not removed. At the same time, the shorter run cycles mean that less air is being pushed through the air filters, so dust reduction (including allergens or other irritating particles) may be reduced too.

2. increased operating costs - from short on-off cycling

3. possibly complaints from occupants if the indoor temperature changes too rapidly or too frequently - a variation on the "short cycling" complaint cited just above

4. Some experts say that occupants may complain of noise - a unit larger than needed may be noisier than needed; I haven't come acoss this complaint.

Here is a nice article on the topic:

Levins, William P., C. Keith Rice, and Van D. Baxter. Modeled and measured effects of compressor downsizing in an existing air conditioner/heat pump in the cooling mode. No. CONF-960606--2. Oak Ridge National Lab., TN (United States), 1996.

On 2015-12-20 y Rick McCall

I inspected a 12 year old, RHEEM ,split heat pump system. The condenser unit's model number is RMPC-042JAZ, indicating to me that it has a cooling capacity of 3 and a half tons. The air handler unit in the attic however appears to be a 2 ton unit.

Since I know that the attic unit should be at least equal in size to the compressor unit, how negatively is this system's performance affected?

On 2015-10-06 by Anwar

How to find out capacity in btu from model number if model number like that LBC362GSA4

On 2015-06-09 by Jim

I have a trane heat pump on my house. It's model number is TWR036C100A3 From this can I assume it's a 3 ton unit from the "36" in the Model#?

On 2015-05-11 by (mod) -

Athmaro, the room temperature produced by an air conditioner depends on specific site conditions such as the building heat gain, outdoor temperatures, sun exposure, amount of glass or windows, ventilation, building size, occupancy, layout, condition of the HVAC duct system, etc. so there is not a single answer.

However if the cooling capacity of the air conditioning system is adequate it will bring the room temperature to the set point on the thermometer and it should be capable of keeping it within a few degrees of that number under most conditions.

Refrigeration gauges and test equipment are used by HVA service technicians and require specific training to use and interpret.

The cooling capacity of the equipment (such as the 1.5 ton capacity you mention) is the manufacturer's rated capacity and is found on the equipment data tag. The actual cooling ability of the system in a specific installation depends on specific site conditions, of which I list some examples just above.

On 2015-05-11 by Athmarao.N.R.

For 1.5 ton capacity a/c -when setting no 16 to xxx-what will be temp prevails in the room during functionig.Also how to check the gass r22 quantity -is there any gauge available and how to acertain for 1.5 ton capacity.

How to ask technician to go about. brand-Fujiair-Malaysia made.

Question: my air conditioner utility bills are too high

(June 16, 2014) Luthenia@gmail.com said:

My air conditioner is not cooling my apartment adequately.

When I set the thermostat at 75 degrees the unit continously runs and the temp does not get below 80 degrees inside at the peak of the day.

The maintenance team looked at the condenser (outside) and found no leaks and said the freon level is where it should be.

Although they have not checked the lines from the condenser to the air handler (inside) for blockage or leaks. Please advise on how to proceed. Also my utility bill is too high.

Reply:

Luthenia,

I'm not sure how the refrigerant "level" was checked (by just looking I wouldn't know the answer to that supposition), but if the refrigerant charge is correct in the unit then most likely it is not leaking refrigerant.

Question: how often do you need to charge your A/C Unit?

(June 21, 2014) Anonymous said:

how do you know when you need to charge your a/c unit

Reply:

Recharging AC refrigerant is not a normal nor regular maintenance chore. Rather, refrigerant may be needed if there has been a leak - and of course it makes sense to find and fix the leak first. Charging is also needed as part of any system repair that nvolves opening the refrigerant oping system.

Question: an AC technician told me what sized system I needin BTUH

(July 16, 2014) LB said:

The central air unit for a 1950's built house in Tucson, AZ is rated at 36,000 btuh. The brick ranch-style house is 1260 sq. ft. with no shade from the E,S, or W.

The original system was swamp cooler w/ductwork added on the roof to reach a later addition, the ground-based ac unit was retro fitted to this system to cool 2 bedrooms, 2 baths, large living room, large kitchen, dining area and den.

An AC tech told me the system should be 42,000 btuh to properly cool with out running constantly on peak days...which it does. Your thoughts?

Reply:

I can't second-guess your on-site AC technician who knows and sees more than we can from just the text of your question. But in general, we don't want to over-size an air conditioner or heat pump. Doing so risks that the system will cool the building so quickly that it will not adequately dehumidify the indoor air.

Question: can't find specifications on cooling area square feet that factor in building ceiling heighbt

(July 17, 2014) rick robinson said:

I am wanting to buy a portable A/C - heating unit, both at 14,000 b.t.u."s.
I want to put it in my garage. w.15'x 15'x 9' high. I don't find specs. on square feet with the height. Is that enough b.t.u.'s for that area ?

Reply:

LB,

While we give some general rules of thumb for determining AC capacity required for a home, Tucson is indeed an area of plenty of solar gain (and a dry climate which makes swamp coolers work pretty well). I figure we ought to take the advice of your service tech who has direct experience in your local area.

In humid climates, over-sizing an AC unit can in fact cause it to fail to dehumidify properly. But in Tucson where the air is dry to start with, that's less of a concern than having adequate cooling.

If you go with the smaller unit you'll find that on the hottest days of the year it may run constantly, possibly being on the margin of adequacy.

Finally, the high ceiling is only a foot higher than most rooms - I don't think that's a big factor.

Question: relationship of RLA and electrical motor horsepower

(Aug 2, 2014) Eng.M.Mossad2010@gmail.com said:

from the part of " FROM EQUIPMENT RLA # - Air Conditioning Equipment Capacity from Equipment RLA Numbers " in the article above can we find a relation between the equipment's RLA and the HP "horse power " for the Compressor motor?

Reply: relationship of RLA, LRA and FLA motor ratings & converting to horsepower

Mossad: for a specific air conditioner or heat pump motor I'd obtain the horsepower rating first by looking at the BTUh rating on the data tag or encoded in the model number. For example, 18,000 BTUh is equivalent to 2 HP (horsepower) or 24,000 = 2.5 HP.

Formula to Convert Electrical Amps to Horspower

1 HP (horsepower) = 745.7 Watts (round to 746 W)

How to Calculate Horsepower from Motor Amperage

We can easily express Amps in a formula to obtain horsepower as follows:

AMPS = ( Horsepower x 746 ) / Voltage

Example: For a 220V electric motor with a 40-Amp LRA or FLA rating

40A = (Horsepower x 746) / V

40 = (HP x 746) / 220 -

then using simple algebra we calculate that this is a 12 horsepower motor based on its LRA or FLA rating.

Complete details are at ELECTRIC MOTOR HORSEPOWER & CIRCUIT WIRE SIZE

Question: installed larger AC but now takes longer to cool the building

(Aug 6, 2014) cookie77037@gmail.com said:

I had a new AC system installed recently in a 900 SqFt home. They upped me from a 2.5 Ton to a high efficiency 3 ton.

They also up sized the blower and now the fab suction has a high air and blower noise and the air coming out of the registers is really coming out at a pretty high velocity relative to the old system.

The system seems to run a longer time now and I am wondering if the blower is over sized for the ducting and the air is retuning to the unit immediately instead of dispersing and cooling the rooms. Sort of short circuiting the process.

Reply:

Cookie

What sounds odd to me is to install a larger capacity AC system yet find that it runs longer to cool the building than previously. Something's probably wrong. Perhaps the air velocity is too great for the design of the cooling coil. I'd give the installing company a call, speak with the service manager, and ask for help by an experienced senior technician.

Question: encoding of cooling capacity on air conditioners & heat pumps

(Sept 6, 2014) jerry said:
I Cant Seem To Get It ,BTUs,Or Tons, Ser No,edcm168896 And Modle No, e1fb036s06a

(Oct 11, 2014) omar said:
Can I get the cooling capacity from serial number

Reply:

Not from the serial number but from the model number on the data tag.

See DATA TAGS on AIR CONDITIONERS

On 2012-10-16 by B.A BASHARAT

Carrier D4DH52500EWK
HOW MUCH KELO GASS R22

On 2012-08-24 by Anonymous

My house is 2484 sq ft. Will Carrier 24ABB336A003 be adequate?

On 2012-08-14 by ml

My 20 year old heat pump is undersized and neither heats nor cools well or efficiently. My utility bills are so high I'm considering selling our home. How much energy savings could I realistically see with a properly sized, newer more efficient unit? We have a 1400 sq. ft. split level house with cathedral ceilings and small 2 ton unit.

On 2012-05-30 by (mod) - Trane TTX760A100A2 cooling capacitdy

Anon, according to Carson Dunlop's Technical Reference Guide (available in the references section at the end of this article) after 2005 the company was reluctant to release general information about date code patterns for their equipment - if you contact them with a specific serial number they will check their records. Trane in the U.S. is at 903-581-3200.

More generally, looking at the number you provided,

TT - indicates a split cooling system
Usually the 5th and 6th characters indicate M BTUH of cooling capacity so for your unit, it looks like

60A = 60,000 BTUs

On 2012-05-29 by Anonymous

Hi I want to replace my Trane TTX760A100A2, do you know what size unit this is?
Thanks

On 2011-08-24 by JC

How do you figure the tonnage based on the amount of condensation the system creates.

On 2011-08-19 by Charles

What are the consequences if the Condenser Unit and the Evaporator Cooler are differnet sizes?

On 2011-07-24 by (mod) -

Alan I can't say with so little information but before deciding that the total cooling capacity is not enough for your home make sure that the equipment is working properly - see the article titled

DIAGNOSE AIR CONDITIONER PROBLEMS found in the ARTICLE INDEX


Chris: should be fine, wired, charged, etc. properly.

On 2011-07-23 by Alan D.

Is a 17 or 18 split adequate for a two unit home? We can not get our brand new home to cool below 77.

On 2011-07-18 by chris

i just got a carrier 4 ton 16 sree out side and a goodman inside 4 ton should these work good together

On 2011-06-02 by (mod) -

Sizing HVAC blower fan motors:

Good question, Chris. If there is no information on the old fan motor itself, and no information about the motor on the equipment data tag (check on the blower fan assembly housing as well as inside the blower cabinet) I can think of one optimum solution to sizing the new blower fan motor and one backup approach:

1. With the brand, model, and serial number of the air handler itself, a quick consult with the installation and service manual, or easier, a quick telephone call to the manufacturer's technical support hot line (usually an 800 number) is how I'd assure I was selecting the proper replacement motor.

2. Companies such as DiversiTech (diversitech dot com or Telephone: 1.800.995.2222) offer electric motors that can support multiple horsepower ratings, allowing rotation direction to be swapped with a simple wiring change, and that provide two rotation speeds (such as we find in blower motors for an air handler that supports both heating and cooling mode).

If another reader has a suggestion on sizing blower fan motors when there is no information data tag on the motor we'd welcome seeing it here.

On 2011-06-02 by Chris

When I encounter a unit, and the fan motor is not working, and there is no tag on the motor, or unit, I want to properly size the new fan motor, for that unit. What is the way to do that?

...

Continue reading at RATED COOLING CAPACITY - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• AIR CONDITIONER TEMPERATURE MEASUREMENT for a discussion of what temperatures to expect at different points in the air conditioning system.
• AIR CONDITIONER BTU CHART - table of BTU requirements by cooling area size & other parameters
• LOST COOLING CAPACITY for diagnosis of poor air conditioner performance, and see This website answers all questions about air conditioning and heat pump systems.
• SEER RATINGS & OTHER DEFINITIONS

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RATED COOLING CAPACITY FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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