The document provides various HVAC formulas and conversion factors essential for heating, ventilation, and air conditioning calculations. It includes formulas for calculating CFM, BTU, horsepower, and efficiencies, along with gas laws and properties of materials. Additionally, it outlines unit conversions between imperial and metric measurements, encompassing linear, area, volume, and heat equivalents.

1. HVAC FORMULAS
CFM = ______BTU/Hr / ( 1.08 x Temperature Difference)
TON OF REFRIGERATION -
The amount of heat required to melt a ton (2000 lbs.) of ice at 32°F
288,000 BTU/24 hr.
12,000 BTU/hr.
APPROXIMATELY 2 inches in Hg. (mercury) = 1 psi
WORK =
Force (energy exerted) X Distance
Example: A 150 lb. man climbs a flight of stairs 100 ft. high
Work = 150 lb. X 100 ft.
Work = 15,000 ft.-lb.
ONE HORSEPOWER =
33,000 ft.-lb. of work in 1 minute
ONE HORSEPOWER =

2. 746 Watts
CONVERTING KW to BTU:
1 KW = 3413 BTU’s
Example: A 20 KW heater (20 KW X 3413 BTU/KW = 68,260 BTU’s)
CONVERTING BTU to KW
3413 BTU’s = 1 KW
Example: A 100,000 BTU/hr. oil or gas furnace
(100,000 / 3413 = 29.3 KW)
COULOMB =
6.24 X 1018 (1 Coulomb = 1 Amp)
OHM'S LAW =
E = I x R
I = E / R
R = E / I
Where:
E = voltage (emf)
I = Amperage (current)

3. R = Resistance (load)
WATTS (POWER) =
volts x amps or P = E x I
P(in KW) = (E x I) / 1000
U FACTOR =
Reciprocal of R factor
1 / R = U
Example:
If R = 19:
U = 1 / 19 = .05 (BTU’s transferred / 1 Sq.Ft. / 1ºF / 1 Hour)
VA
(how the secondary of a transformer is rated) = volts X amps
Example: 24V x .41A = 10 VA

4. ONE FARAD CAPACITY =
1 amp. stored under 1 volt of pressure
MFD (microfarad) =
1 MFD = 1 Farad / 1,000,000
LRA (Locked rotor amps) =
LRA = FLA x 5 (NOTE: This is a commonly used rule-of-thumb, not a direct conversion)
TEV (shown in equilibrium)
46.7# (Bulb Pressure) = 9.7# (Spring Pressure) + 37# (Evaporator Pressure)
Where:
Bulb Pressure = opening force
Spring and Evaporator Pressures = closing forces
RPM of motor = (60Hz x 120) / (No. of Poles)
1800 RPM Motor – slippage makes it about 1750
3600 RPM Motor – slippage makes it about 3450

5. DRY AIR =
78.0% Nitrogen
21.0% Oxygen
1.0% Other Gases
WET AIR =
Same as dry air plus water vapor
SPECIFIC DENSITY = 1 / Specific Volume
SPECIFIC DENSITY OF AIR = 1 / 13.33 = .075 lbs./cu.ft.
STANDARD AIR =
24 Specific Heat (BTU’s needed to raise 1 lb. 1 degree)
SENSIBLE HEAT FORMULA (Furnaces):
BTU/hr. – Specific Heat X Specific Density X 60 min./hr. =
X CFM X DT
.24 X .075 X 60 X CFM X DT = 1.08 X CFM X DT

6. ENTHALPHY = h =
Sensible heat + Latent heat
TOTAL HEAT FORMULA
(for cooling, humidifying or dehumidifying)
BTU/hr. = Specific Density X 60 min./hr. X CFM X Dh
= 0.75 x 60 x CFM x Dh
= 4.5 x CFM x Dh
Where Dh = Change in Enthalpy
RELATIVE HUMIDITY =
Moisture present / Moisture air can hold
SPECIFIC HUMIDITY =
Grains of moisture per dry air
7000 GRAINS in 1 lb. of water

7. DEW POINT =
When wet bulb equals dry bulb
TOTAL PRESSURE (Ductwork) =
Static Pressure + Velocity Pressure
CFM =
Area (sq. ft.) X Velocity (ft. min.)
HOW TO CALCULATE AREA
Rectangular Duct
A = L x W
Round Duct
A = (Pi)r² ...or...(Pi)D²/4
RETURN AIR GRILLES –
Net free area = about 75%
3 PHASE VOLTAGE UNBALANCE =
(100 x maximum deg. from average volts) / Average Volts

8. NET OIL PRESSURE =
Gross Oil Pressure – Suction Pressure
NOTE: The suction pressure must be measured at the crankcase, not the service valve
COMPRESSION RATIO =
Discharge Pressure Absolute / Suction Pressure Absolute
HEAT PUMP AUXILIARY HEAT –
Sized at 100% of load
ARI HEAT PUMP RATING POINTS =
47°F and 17°F
NON-BLEND REFRIGERANTS:
Constant Pressure = Constant Temperature during
Saturated Condition in an evaporator or condenser
BLENDS –

9. Changing Temperature during Saturated Condition in an evaporator or condenser (See Glide)
28 INCHES OF WC =
1 psi
NATURAL GAS COMBUSTION:
Excess Air = 50%
15 ft.3 of air to burn 1 ft.3 of methane produces:
16 ft.3 of flue gases:
1 ft.3 of oxygen
12 ft.3 of nitrogen
1 ft.3 of carbon dioxide
2 ft.3 of water vapor
Another 15 ft.3 of air is added at the draft hood
GAS PIPING (Sizing – CF/hr.) =
Input BTU’s
Heating Value
Example:
80,000 Input BTU’s
1000 (Heating Value per CF of Natural Gas)
= 80 CF/hr.

10. Example:
80,000 Input BTU’s
2550 (Heating Value per CF of Propane)
= 31 CF/hr.
FLAMMABILITY LIMITS
Propane Butane Natural Gas
2.4-9.5 1.9-8.5 4-14
COMBUSTION AIR NEEDED
(PC=Perfect Combustion)
(RC=Real Combustion)
Propane
23.5 ft.3 (PC)
36 ft.3 (RC)
Natural Gas
10 ft.3 (PC)
15 ft.3 (RC)

11. ULTIMATE CO2 13.7% 11.8%
CALCULATING OIL NOZZLE SIZE (GPH):
BTU Input = Nozzle Size (GPH)
140,000 BTU’s
OR
BTU Output
140,000 X Efficiency of Furnace
FURNACE EFFICIENCY:
% Efficiency = energy output / energy input
OIL BURNER STACK TEMPERATURE (Net) =
Highest Stack
Temperature minus
Room Temperature
Example: 520° Stack Temp. – 70° Room Temp. = Net Stack
Temperature of 450°
KELVIN TO CELSIUS:
C = K – 273

12. CELSIUS TO KELVIN:
K = C + 273
ABSOLUTE TEMPERATURE MEASURED IN KELVINS
SINE = side opposite
COSINE = side adjacent
Sin = hypotenuse
Cos = hypotenuse
TANGENT =
side opposite / side adjacent
PERIMETER OF SQUARE:
P = 4s
Where: P = Perimeter and s = side
PERIMETER OF RECTANGLE:
P = 2l + 2w P – Perimeter
l = length

13. w = width
PERIMETER OF SQUARE
P = a + b + c + d (P = Perimeter)
a = 1st side
b = 2nd side
c = 3rd side
d= 4th
side
PERIMETER OF CIRCLE:
C = (Pi)D = 2(Pi)r
Where:
C = Circumference
(Pi) = 3.1416
D = Diameter
r = radius
AREA OF SQUARE:
a = s² = s x s
A = Area
s = side

14. AREA OF RECTANGLE:
A = l x w
Where:
A = Area
l = length
w = width
AREA OF TRIANGLE:
A = 1/2bh
Where:
A = Area
b = base
h = height
AREA OF CIRCLE:
A = (Pi)r² = (Pi) D²/4
Where:
A = Area
(Pi) = 3.1416
r = radius
D = Diameter

15. VOLUME OF RECTANGULAR SOLID:
V = l x w x h
Where:
V = Volume
l = length
w = width
h = height
VOLUME OF CYLINDRICAL SOLID:
V = (Pi)r²h = (Pi) D²/4 x h
Where:
V = Volume
p = 3.1416
r = Radius
D = Diameter
h = height
CAPACITANCE IN SERIES:
C = 1 / (C1 + C2)

16. CAPACITANCE IN PARALLEL:
C = C1 + C2 + . . . . .
GAS LAWS:
Boyle’s Law: P1 V1 = P2 V2
Where:
P = Pressure (absolute)
V = Volume
Charles’ Law:
P1 / T1 = P2 / T2
Where:
P = Pressure (absolute)
T = Temperature (absolute)
General Gas Law:
(P1 x V1) / T1 = (P2 x V2) / T2
Where:
P = Pressure (absolute)
V = Volume

17. T = Temperature (absolute)
PYTHAGOREAN THEOREM:
c2 = a2 + b2
Where:
c = hypotenuse
a & b = sides
Capacity of Schedule 80 steel pipe in foot per length in US gallons:
1” = .0374
1-1/4” = .0666
1-1/2” = .0918
2” = .1535
2-1/2” = .22
3” = .344
4” = .5970
5” = .947
Example 2-1/2" pipe = .22 x 10 feet = 2.2 gallons capacity
Infrared Thermometer Adjustment Values:
Material/Emissivity
Aluminum
Bright/0.09

18. Anodized/0.55
Oxidized/0.2 to 0.3
Brass
Bright/0.03
Oxidized/0.61
Chromium
Polished/0.08
Copper
Bright/0.05
Oxidized/0.78
Iron and Steel
Polished/0.55
Oxidized/0.85
Nickel
Polished/0.05
Oxidized/0.95
Zinc
Bright/0.23
Oxidized/0.23
Brick
Building/0.45
Paints
White/0.9
Black/0.86
Oil Paints (all)/0.92

19. Roofing Paper /0.91
Rubber /0.94
Silica /0.42 to 0.62
Water /0.92
Weights and Specific Heats of Substances
Material/Weight (Ib./ft³)/Specific Heat (Btu/lb)
Gases
Air (normal temp)/0.075/0.24
Metals
Aluminum/166.5/0.214
Copper/552/0.094
Iron/480/0.118
Lead/710/0.030
Mercury/847/0.033
Steel/492/0.117
Zinc/446/0.096
Liquids
Alcohol/49.6/0.60
Glycerin/83.6/0.576
Oil/57.5/0.400
Water/62.4/1.000

20. Others
Concrete/147/0.19
Cork/15/0.48
Glass/164/0.199
Ice/57.5/0.504
Masonry/112/0.200
Paper/58/0.324
Rubber/59/0.48
Sand/100/0.195
Stone/138-200/0.20
Tar/75/0.35
Wood, Oak/48/0.57
Wood, Pine/38/0.47
Linear Measurement Equivalents (U.S. Conventional - SI Metric)
1 inch =
2.54 cm
25.4 mm
25400 µm
1 foot =
12"
0.304 m
30.48 cm

21. 1 yard =
3'
0.914 m
91.44 cm
1 micron =
0.0000394"
1 millimeter =
1000 µm
0.0394"
1 centimeter =
10 mm
0.3937"
1 meter =
100 cm
39.37"
1 kilometer =
1000m
0.62137 miles
Area Equivalents ( U.S. to Metric )

22. 1 in²=
0.0065m²
1 ft²=
144 in²
0.093 m²
1 yd²=
1296 in²=
9 ft²=
0.836 m²
Volume Equivalents ( U.S. and Metric )
1 in³=
0.016 L=
16.39 cm³
1 ft³=
1728 in³=
7.481 gal=
28.317 L=
0.0283 m³=
28317 cm³

23. 1 yd³=
27 ft³=
46656 in³
1 gal=
0.1337 ft³=
3.79 L=
231 in³=
3785 cm³
1 cm³=
0.0610237 in³
1 L=
61.03 in³
1000 cm³
0.2642 gal
Velocity Equivalents
1 mi/hr=
1.47 ft/sec
0.87 knot
1.61 km/hr

24. 0.45m/sec
1 ft/sec=
0.68 mi/hr
60 ft/min
0.59 knot
o 1.1 km/hr
0.305 m/sec
1 m/sec=
3.28 ft/sec
2.24 mi/hr
1.94 knot
3.6 km/hr
1 km/hr=
0.91 ft/sec
0.62 mi/hr
0.54 knot
0.28 m/sec
Heat Equivalents
1 Btu=

25. 252 calories
1054.4 J (Joules)
1 kcal (kilocalorie)=
1000 cal
4.1840 kJ
1 Btu/lb=
0.5556 kcal/kg
2.3244 kJ/kg
1kcal/kg=
1.8 Btu/lb
Btu/hr=
0.2931W