Memorandum

To: Docket EPA-HQ-OAR-2013-0748

From: Gerald Wozniak, Margaret Sheppard, and Dave Godwin

EPA/Stratospheric Protection Division

Subject: Derivation of Charge Limits for Room Air Conditioners

Date: May 27, 2014

This document describes how EPA derived the refrigerant charge limits for room air 

conditioners and heat pumps proposed in “Protection of Stratospheric Ozone: Listing of 

Substitutes for Refrigeration and Air Conditioning and Revision of the Venting Prohibition for 

Certain Refrigerant Substitutes.”

Source documents for calculations

These charge limits are based upon calculations from formulas in Underwriters 

Laboratories (UL) standard 484, Room Air Conditioners. The formulas in Appendix F of the UL 

484 standard in turn are based upon the international industry standard International 

Electrotechnical Commission (IEC) 60335-2-40, “Particular Requirements for Electrical Heat 

Pumps, Air Conditioners and Dehumidifiers” (2005). Kataoka, et al. (2000) first derived these 

formulas and discussed their technical basis. These formulas are empirically derived, considering

molecular mass, lower flammability limit, refrigerant dispersion, leak rates, and the dimensions 

of the space that refrigerant leaks into. These formulas also were proposed to the IEC SC 61D 

and International Organization for Standardization (ISO) TC86 SC1 WG1 joint working groups 

to assist in setting standards for using flammable refrigerants in air conditioning equipment and 

dehumidifiers (Kataoka et al., 2000).

Formula used to establish limits

The formula from appendix F of UL 484 (section 1.6), “Requirements for Charge 

Limits,” is for appliances with charge amounts m1 < M < m2, where M is the refrigerant charge 

amount in appliance in kg, m1 is 4m3x the lower flammability limit (LFL) in kg/m3, and m2 is 

26m3x LFL. The formula for the maximum allowable charge size is as follows:
 = 2.5 ()



 h√

Where,

mmax = the maximum allowable charge size allowed for the space, in kg,

LFL = the lower flammability limit of the refrigerant in kg/m3,

h0 = the installation height of the indoor unit in m (0.6 m for an air conditioning (AC)

unit on the floor, 1.0 m for an AC unit in a window, 1.8 m for a wall-mounted AC 

unit, and 2.2 m for a ceiling-mounted AC unit)

A = the area of the room, in m2

The formulas are based upon the conservative assumption that the ceiling of the room is 

2.2 m (8 ft) high. The formulas are designed to prevent exceedance of 25% of the LFL.

EPA used the following methodology to derive the maximum allowable charge limits by

means of the aforementioned equation. This approach included examining the charge limit with

respect to the LFLs of different refrigerants, while taking into consideration variables such as the 

installation height (h0) of the AC unit and the area of the room.

Source of values in the formula for maximum allowable charge size

Lower Flammability Limit (LFL) values

EPA used the following information in calculating the lower flammability limit on the basis of 

mass per unit volume (kg/m3), abbreviated LFLm.

Refrigerant 

designation

IUPAC chemical 

name or blend 

composition

Molar mass 

(kg/kmol)

LFLm in

kg/m3

LFLv in % 

v/v

R-290 Propane 44.1 0.038 2.1%

R-32 Difluoromethane 52 0.306 14.4%

R-441A 290/600/600a/170 

(60/30/5/5)

48.44 0.041 2.05%

For R-290 and R-32, the LFLm values are listed in Appendix B of UL 484. For R-441A, EPA 

used the LFL as a percentage of volume per volume from A.S. Trust & Holdings’ SNAP 

submission (2.05%) and calculated the LFLm from the LFLv using the following formula:

LFLm = (MM/24.4) x LFLv x 1000

Where, 

LFLm = lower flammability limit in kg/m3(0.041),

MM = molecular mass in kg/mol (0.04844),

LFLv = lower flammability limit as a percentage volume (0.0205),

24.4 = conversion factor, 1 mole of a gas per 24.4 liters at standard temperature (32oF, 

0oC) and pressure (1 atmosphere, 101.325 kPa), based on the ideal gas law,
1000 = conversion factor, 1000 liters per m

3

Installation Height (h0) values

Appendix F in the UL 484 standard sets four installation heights for a unit: 0.6 m for an 

AC unit on the floor, 1.0 m for an AC unit in a window, 1.8 m for a wall-mounted AC unit, and 

2.2 m for a ceiling-mounted AC unit. In terms of determining if concentrations are small enough 

to remain below the LFL if the refrigerant is released, a greater compressor height h0 corresponds 

with better mixing of the refrigerant throughout a room. For example, a release of refrigerant 

near the ceiling will be more thoroughly mixed and there will be lower concentrations than if the 

same refrigerant charge is released close to the floor.

EPA established the tables of proposed charge limits with h0 values that correspond to the 

following room air conditioner types:

 h0=0.6 m: packaged terminal air conditioners (PTACs), packaged terminal heat 

pumps (PTHPs), and portable air conditioners (all units on or near floor)

 h0=1.0 m: window AC units

 h0=1.8 m: wall-mounted AC units

 h0=2.2 m: ceiling-mounted AC units
Correlation of AC unit capacity and room area 

After determining the LFLm and installation heights the EPA used approximation of 

appropriate capacities for cooling a given area. The capacities for cooling a given area of a room 

is based upon the following table from EnergyStar 2014:

Area To Be Cooled (ft2) Capacity Needed (BTUs/hour) 

100 up to 150 5,000

150 up to 250 6,000

250 up to 300 7,000

300 up to 350 8,000

350 up to 400 9,000

400 up to 450 10,000

450 up to 550 12,000

550 up to 700 14,000

700 up to 1,000 18,000

1,000 up to 1,200 21,000

1,200 up to 1,400 23,000

1,400 up to 1,500 24,000

1,500 up to 2,000 30,000

2,000 up to 2,500 34,000

EPA used the correlations below in associating capacity with room area. We used a 

conversion factor of 0.092903 m2/ft2. EPA established the tables of proposed charge limits with 

respect to the minimum area required for a maximum charge that correspond to the room air 

conditioner type.
Area To Be Cooled

range (ft2) min (ft2) max (ft2) min (m

2

) max (m

2

) Capacity

(BTU/hr)

100 up to 150 100 150 9.3 13.9 5,000

150 up to 250 150 250 13.9 23.2 6,000

250 up to 300 250 300 23.2 27.9 7,000

300 up to 350 300 350 27.9 32.5 8,000

350 up to 400 350 400 32.5 37.2 9,000

400 up to 450 400 450 37.2 41.8 10,000

450 up to 550 450 550 41.8 51.1 12,000

550 up to 700 550 700 51.1 65.0 14,000

700 up to 1,000 700 1,000 65.0 92.9 18,000

1,000 up to 1,200 1000 1,200 92.9 111.4 21,000

1,200 up to 1,400 1200 1,400 111.5 130.1 23,000

1,400 up to 1,500 1400 1,500 130.1 139.4 24,000

1,500 up to 2,000 1500 2,000 139.4 185.8 30,000

2,000 up to 2,500 2000 2,500 185.8 232.3 34,000

Sources of uncertainty in capacity value 

EPA’s EnergyStar program website also suggests some adjustments to capacity to 

address additional factors that may increase or decrease cooling capacity needed for a room:

o If the room is heavily shaded, reduce capacity by 10 percent.

o If the room is very sunny, increase capacity by 10 percent.

o If more than two people regularly occupy the room, add 600 BTUs for each additional 

person.

o If the unit is used in a kitchen, increase capacity by 4,000 BTUs.

The calculations used to derive the charge sizes in EPA’s proposed rule do not adjust for these 

additional factors.
Proposed charge limits 

Table A below illustrates the maximum design charge sizes (kg) for window air conditioners 

with an installation height equal to 1m for different cooling capacities. Table B illustrates the 

maximum design charge sizes (kg) for PTACs, PTHPs and portable air conditioning units with 

an installation height equal to 0.6 m. Table C illustrates the maximum design charge sizes (kg) 

for wall mounted AC units with an installation height equal to 1.8 m. Table D illustrates the 

maximum design charge sizes (kg) for ceiling-mounted AC units with an installation height 

equal to 2.2m. These tables clearly indicate that charge sizes will slightly increase as a result of 

the installation height of the unit. For example, the charge size of 1.73 kg for R-32 in Table A

(the lowest installation height) is much smaller than the charge size of 3.82 kg for R-32 in Table 

D (the highest installation height). It is also important to note that these charge sizes were 

derived with respect to the minimum room area for a given capacity and thus these calculations 

are based on a conservative analysis. For example, if the maximum room area was considered, it 

would yield a slightly higher maximum design charge size.

The UL standard indicates that the formula used above is for appliances with charge sizes in a 

given range of m1 and m2. As indicated on page 1 of this memo, m2 is 26 m3 x LFL. Therefore, 

the calculations of allowable charge size, shown in Tables A through D, must be checked to 

ensure the values remain below m2. Although this limit is not reached in Tables A and B, it is 

reached in Tables C and D; those values are marked with an asterisk (*). Specifically, these 

maximum charge limits will apply and supersede those in the Tables C and D:

 In Table E, for R-32, for capacities >= 18,000 BTU/hr: 7.956 kg.

 In Table E, for R-290, for capacities = 34,000 BTU/hr: 0.988 kg.

 In Table E, for R-441A, for capacities = 34,000 BTU/hr: 1.066 kg.

 In Table F, for R-32, for capacities >= 12,000 BTU/hr: 7.956 kg.

 In Table F, for R-290, for capacities >= 24,000 BTU/hr: 0.988 kg.

 In Table F, for R-441A, for capacities >= 23,000 BTU/hr: 1.066 kg.

Incorporating these results, Tables E and F present the maximum charge size limits for wallmounted and ceiling-mounted room air conditioners, respectively.
The proposed charge limits are stated below in Tables A, B, E and F. (Values published in the notice of proposed rulemaking are rounded to 

the nearest tenth of a kilogram, rather than the nearest gram.)

Table A. Maximum Design Charge Sizes for Window Air Conditioners

Refrigerant

Maximum design charge size (kg)

Associated cooling capacity (BTU/hr)

5,000 6,000 7,000 8,000 9,000 10,000 12,000 14,000 18,000 21,000 23,000 24,000 30,000 34,000

R-32 1.734 2.124 2.742 3.004 3.244 3.468 3.679 4.067 4.588 5.484 6.008 6.489 6.717 7.756

R-290 0.128 0.157 0.202 0.221 0.239 0.256 0.271 0.300 0.338 0.404 0.443 0.478 0.495 0.572

R-441A 0.141 0.172 0.222 0.243 0.263 0.281 0.298 0.330 0.372 0.445 0.487 0.526 0.544 0.629

Note: For use with self-contained air conditioning units or heat pumps with an evaporator at least 0.6 and no more than 1.0 m above the floor. (Assumes h0=1.0 

m) 

Cooling capacities between those in the table are to be linearly interpolated between the next smaller and larger capacities listed in the table.

Table B. Maximum Design Charge Sizes for Packaged Terminal Air Conditioners, 

Packaged Terminal Heat Pumps, and Portable Air Conditioning Units

Refrigerant

Maximum design charge size (kg)

Associated cooling capacity (BTU/hr)

5,000 6,000 7,000 8,000 9,000 10,000 12,000 14,000 18,000 21,000 23,000 24,000 30,000 34,000

R-32 1.041 1.274 1.645 1.802 1.947 2.081 2.207 2.440 2.753 3.290 3.605 3.893 4.030 4.653

R-290 0.077 0.094 0.121 0.133 0.144 0.153 0.163 0.180 0.203 0.243 0.266 0.287 0.297 0.343

R-441A 0.084 0.103 0.133 0.146 0.158 0.169 0.179 0.198 0.223 0.267 0.292 0.316 0.327 0.377

Note: For use with self-contained air conditioning units or heat pumps with an evaporator no more than 0.6 m above the floor. (Assumes h0=0.6 m) 

Cooling capacities between those in the table are to be linearly interpolated between the next smaller and larger capacities listed in the table.
Table C. Derived Maximum Design Charge Sizes for Wall-Mounted AC Units 

Refrigerant Maximum design charge size (kg)

Associated cooling capacity (BTU/hr)

5,000 6,000 7,000 8,000 9,000 10,000 12,000 14,000 18,000 21,000 23,000 24,000 30,000 34,000

R-32 3.122 3.823 4.936 5.407 5.840 6.243 6.622 7.321 8.259* 9.871* 10.814* 11.680* 12.090* 13.960*

R-290 0.230 0.282 0.364 0.399 0.431 0.460 0.488 0.540 0.609 0.728 0.797 0.861 0.891 1.029*

R-441A 0.253 0.310 0.400 0.438 0.473 0.506 0.537 0.593 0.670 0.800 0.877 0.947 0.980 1.132*

Note: For use with self-contained air conditioners or heat pumps with an evaporator at least 1.0 and no more than 1.8 m above the floor. (Assumes h0=1.8 m) 

Cooling capacities between those in the table are to be linearly interpolated between the next smaller and larger capacities listed in the table.

See Table E for maximum charge sizes for those above marked with an asterisk (*).

Table D. Derived Maximum Design Charge Sizes for Ceiling-Mounted AC Units: 

Refrigerant

Maximum Design Charge Size (kg)

Associated capacity (BTU/hr)

5,00

0

6,000 7,000 8,000 9,000 10,000 12,000 14,000 18,000 21,000 23,000 24,000 30,000 34,000

R-32 3.81

5

4.673 6.033 6.608 7.138 7.631 8.093* 8.948* 10.094

*

12.065

*

13.217

*

14.276

*

14.777

*

17.063*

R-290 0.28

1

0.344 0.445 0.487 0.526 0.563 0.597 0.660 0.744 0.889 0.974 1.052* 1.089* 1.258*

R-441A 0.30

9

0.379 0.489 0.536 0.579 0.619 0.656 0.725 0.818 0.978 1.071* 1.157* 1.198* 1.383*

Note: For use with self-contained air conditioners or heat pumps with an evaporator more than 1.8 m above the floor. (Assumes h0=2.2 m) 

Cooling capacities between those in the table are to be linearly interpolated between the next smaller and larger capacities listed in the table.

See Table F for maximum charge sizes for those above marked with an asterisk (*).
Table E. Maximum Design Charge Sizes for Wall-Mounted AC Units

Refrigerant Maximum design charge size (kg)

Associated cooling capacity (BTU/hr)

5,000 6,000 7,000 8,000 9,000 10,000 12,000 14,000 18,000 21,000 23,000 24,000 30,000 34,000

R-32 3.122 3.823 4.936 5.407 5.840 6.243 6.622 7.321 7.956 7.956 7.956 7.956 7.956 7.956

R-290 0.230 0.282 0.364 0.399 0.431 0.460 0.488 0.540 0.609 0.728 0.797 0.861 0.891 0.988

R-441A 0.253 0.310 0.400 0.438 0.473 0.506 0.537 0.593 0.670 0.800 0.877 0.947 0.980 1.066

 

Note: For use with self-contained air conditioners or heat pumps with an evaporator at least 1.0 and no more than 1.8 m above the floor. (Assumes h0=1.8 m) 

Cooling capacities between those in the table are to be linearly interpolated between the next smaller and larger capacities listed in the table.

Table F. Maximum Design Charge Sizes for Ceiling-Mounted AC Unit

Refrigerant

Maximum Design Charge Size (kg)

Associated capacity (BTU/hr)

5,000 6,000 7,000 8,000 9,000 10,000 12,000 14,000 18,000 21,000 23,000 24,000 30,000 34,000

R-32 3.815 4.673 6.033 6.608 7.138 7.631 7.956 7.956 7.956 7.956 7.956 7.956 7.956 7.956

R-290 0.281 0.344 0.445 0.487 0.526 0.563 0.597 0.660 0.744 0.889 0.974 0.988 0.988 0.988

R-441A 0.309 0.379 0.489 0.536 0.579 0.619 0.656 0.725 0.818 0.978 1.066 1.066 1.066 1.066

Note: For use with self-contained air conditioners or heat pumps with an evaporator more than 1.8 m above the floor. (Assumes h0=2.2 m) 

Cooling capacities between those in the table are to be linearly interpolated between the next smaller and larger capacities listed in the table.
Conversion to English units of measure

For the readers’ information, we provide the same maximum design charge sizes as above converted to ounces, using the conversion factor 35.274 oz/kg.

Maximum Design Charge Sizes in Ounces for Window Units

Capacity (BTU/hr)

Refrigerant 5,000 6,000 7,000 8,000 9,000 1,0000 12,000 14,000 18,000 21,000 23,000 24,000 3,0000 34,000

R-32 61.17 74.92 96.72 105.96 114.44 122.35 129.77 143.46 161.85 193.45 211.91 228.89 236.92 273.57

R-290 4.51 5.52 7.13 7.81 8.44 9.02 9.57 10.58 11.93 14.26 15.62 16.87 17.47 20.17

R-441A 5.26 6.45 8.32 9.12 9.85 10.53 11.16 12.34 13.92 16.64 18.23 19.69 20.38 23.54

Maximum Design Charge Sizes in Ounces for PTACs/PTHPs

Capacity (BTU/hr)

Refrigerant 5,000 6,000 7,000 8,000 9,000 1,0000 12,000 14,000 18,000 21,000 23,000 24,000 3,0000 34,000

R-32 36.70 44.95 58.03 63.57 68.67 73.41 77.86 86.08 97.11 116.07 127.15 137.33 142.15 164.14

R-290 2.71 3.31 4.28 4.69 5.06 5.41 5.74 6.35 7.16 8.56 9.37 10.12 10.48 12.10

R-441A 3.16 3.87 4.99 5.47 5.91 6.32 6.70 7.41 8.35 9.99 10.94 11.82 12.23 14.12
Maximum Design Charge Sizes in Ounces for Wall-Mounted Units

Refrigerant Capacity (BTU/hr)

5,000 6,000 7,000 8,000 9,000 1,0000 12,000 14,000 18,000 21,000 23,000 24,000 3,0000 34,000

R-32 110.11 134.86 174.10 190.72 206.00 220.22 233.58 258.23 280.64 280.64 280.64 280.64 280.64 280.64

R-290 8.12 9.94 12.83 14.06 15.19 16.23 17.22 19.04 21.48 25.67 28.12 30.37 31.44 34.85

R-441A 8.93 10.93 14.11 15.46 16.70 17.85 18.94 20.93 23.62 28.23 30.92 33.40 34.57 37.60

Maximum Design Charge Sizes in Ounces for Ceiling Mounted Units

Capacity (BTU/hr)

Refrigerant 5,000 6,000 7,000 8,000 9,000 1,0000 12,000 14,000 18,000 21,000 23,000 24,000 3,0000 34,000

R-32 134.58 164.83 212.79 233.10 251.78 269.16 280.64 280.64 280.64 280.64 280.64 280.64 280.64 280.64

R-290 9.92 12.15 15.69 17.18 18.56 19.84 21.05 23.27 26.25 31.37 34.37 34.85 34.85 34.85

R-441A 10.91 13.36 17.25 18.90 20.41 21.82 23.14 25.59 28.86 34.50 37.60 37.60 37.60 37.60
References

Energy Star, “Properly Sized Room Air Conditioners.” Available at 

http://www.energystar.gov/?c=roomac.pr_properly_sized; accessed May 8, 2014.

IEC 60335-2-40, “Particular Requirements for Electrical Heat Pumps, Air Conditioners 

and Dehumidifiers.” 2005.

Kataoka, O., Yoshizawa, M. and Hirakawa, T. 2000. Allowable charge calculation 

method for flammable refrigerants. International Refrigeration and Air Conditioning 

Conference, Purdue University, West Lafayette IN, USA. 2000. Available online at 

http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1505&context=iracc

UL 484, Room Air Conditioners. Appendix F, “Requirements for Charge Limits.” 8

th

Edition. August 2012.