OH HVAC Contractor cheat sheet

Sensible heat formula: Q (Btu/h) = 1.08 × CFM × ΔT for standard air at sea level; latent heat: Q = 0.68 × CFM × ΔW (grains/lb).

Total heat of air: Q = 4.5 × CFM × Δh, where h is enthalpy in Btu/lb of dry air.

Superheat = suction line temperature minus saturated suction temperature at measured suction pressure; target 8-12°F at evaporator outlet for TXV systems.

Subcooling = saturated condensing temperature minus liquid line temperature; a low subcooling with bubbles in the sight glass indicates undercharge.

Refrigerant glide exists in zeotropic blends (R-410A, R-407C); use dew point for superheat and bubble point for subcooling on the same blend.

Standard airflow rule: 400 CFM per ton nominal cooling; latent capacity drops sharply below about 350 CFM/ton.

Duct static budget: typical residential supply static 0.1 in. w.c., return 0.05 in. w.c.; total external static pressure commonly 0.5 in. w.c.

Combustion air: Category I appliances need 50 cu ft per 1,000 Btu/h input for unconfined spaces; two permanent openings sized 1 sq in. per 1,000 Btu/h each.

Refrigerant safety groups per ASHRAE 34: A1 (R-410A, R-134a) lower toxicity, no flame propagation; A2L (R-32, R-454B) lower flammability.

Water column pressure: 1 psi = 2.31 ft of head; pump head in feet divided by 2.31 gives psi.

Hydronic heat delivery: Q (Btu/h) = 500 × GPM × ΔT for water; 485 × GPM × ΔT for 30% glycol, 450 for 50% glycol.

BTU output of a boiler equals GPM × 500 × ΔT; a 20°F design ΔT is standard for residential baseboard loops.

Expansion tank sizing uses acceptance volume: bladder tanks sized from system volume, fill pressure, and maximum pressure; precharge equals fill pressure.

Relief valve setting must not exceed the working pressure rating of any component in the system; typical residential hydronic relief is 30 psi.

Backflow protection: an RPZ is required for high-hazard cross-connections; a double check valve assembly is allowed only for low hazard.

Fixture unit method per ASPE: 1 water closet = 2.5 WSFU, lavatory = 1 WSFU, bathtub = 4 WSFU; convert total WSFU to GPM using the Hunter curve.

Slope of horizontal drainage pipe less than 3 in. diameter is 1/4 in. per foot; 4 in. and larger may use 1/8 in. per foot.

Water heater T&P relief valve discharge must terminate not more than 6 in. above the floor or to the exterior and must not be trapped.

Ohm's law: E = I × R; power: P (watts) = E × I; single-phase P = E × I × PF for reactive loads.

Three-phase power: P = 1.732 × E × I × PF; use 1.732 for balanced three-phase calculations.

Motor full-load current comes from NEC Tables 430.248 (single-phase) and 430.250 (three-phase); branch-circuit conductors sized at 125% of FLC.

Motor overload protection is sized separately from short-circuit and ground-fault protection; overloads protect the motor, breakers protect the conductors.

Conductor ampacity must be corrected for ambient temperature and adjusted for more than three current-carrying conductors in a raceway.

Equipment grounding conductor sizing follows NEC Table 250.122 and is based on the rating of the overcurrent device, not the conductor ampacity.

Voltage drop single-phase: VD = 2 × K × I × L / CM; three-phase uses 1.732 in place of 2. K = 12.9 for copper, 21.2 for aluminum.

GFCI protection is required in bathrooms, garages, outdoors, kitchens, and within 6 ft of sinks; AFCI is required for most 120-volt branch circuits in dwellings.

Disconnecting means for a motor must be within sight of the motor and controller, and a nameplate-rated horsepower switch must be used.

ORC Chapter 4740 governs Ohio's heating, ventilating, air conditioning, and refrigeration contractors; the Ohio Construction Industry Licensing Board (OCILB) administers licensing.

A license is required to advertise or contract for HVAC, refrigeration, plumbing, hydronics, or electrical work in Ohio; local jurisdictions may not require a separate license for work covered by a state license.

Applicants for the HVAC contractor license must document at least 5 years of business experience in the trade, or equivalent education and experience acceptable to the board.

Examination is required and passing scores are set by the board; a passing exam result remains valid for a limited period before the license must be issued.

Continuing education is required for renewal; the board sets the hours and content categories, and certificates of completion must be retained.

Contractors must maintain a surety bond and proof of liability insurance as a condition of licensure and renewal.

Responsible person: the licensed contractor must be actively engaged in and responsible for the work; the license is not transferable to another person or entity.

Unlicensed practice is subject to civil penalties and injunctive action by the board, and the board may suspend, revoke, or refuse to renew a license for violations.

License renewal and reinstatement deadlines, fees, and late penalties are set by the board in administrative rule; a lapsed license cannot be used to pull permits.

Sensible heat formula: Q (Btu/h) = 1.08 × CFM × ΔT for standard air at sea level; latent heat: Q = 0.68 × CFM × ΔW (grains/lb).

Total heat of air: Q = 4.5 × CFM × Δh, where h is enthalpy in Btu/lb of dry air.

Superheat = suction line temperature minus saturated suction temperature at measured suction pressure; target 8-12°F at evaporator outlet for TXV systems.

Subcooling = saturated condensing temperature minus liquid line temperature; a low subcooling with bubbles in the sight glass indicates undercharge.

Refrigerant glide exists in zeotropic blends (R-410A, R-407C); use dew point for superheat and bubble point for subcooling on the same blend.

Standard airflow rule: 400 CFM per ton nominal cooling; latent capacity drops sharply below about 350 CFM/ton.

Duct static budget: typical residential supply static 0.1 in. w.c., return 0.05 in. w.c.; total external static pressure commonly 0.5 in. w.c.

Combustion air: Category I appliances need 50 cu ft per 1,000 Btu/h input for unconfined spaces; two permanent openings sized 1 sq in. per 1,000 Btu/h each.

Refrigerant safety groups per ASHRAE 34: A1 (R-410A, R-134a) lower toxicity, no flame propagation; A2L (R-32, R-454B) lower flammability.

Water column pressure: 1 psi = 2.31 ft of head; pump head in feet divided by 2.31 gives psi.

Hydronic heat delivery: Q (Btu/h) = 500 × GPM × ΔT for water; 485 × GPM × ΔT for 30% glycol, 450 for 50% glycol.

BTU output of a boiler equals GPM × 500 × ΔT; a 20°F design ΔT is standard for residential baseboard loops.

Expansion tank sizing uses acceptance volume: bladder tanks sized from system volume, fill pressure, and maximum pressure; precharge equals fill pressure.

Relief valve setting must not exceed the working pressure rating of any component in the system; typical residential hydronic relief is 30 psi.

Backflow protection: an RPZ is required for high-hazard cross-connections; a double check valve assembly is allowed only for low hazard.

Fixture unit method per ASPE: 1 water closet = 2.5 WSFU, lavatory = 1 WSFU, bathtub = 4 WSFU; convert total WSFU to GPM using the Hunter curve.

Slope of horizontal drainage pipe less than 3 in. diameter is 1/4 in. per foot; 4 in. and larger may use 1/8 in. per foot.

Water heater T&P relief valve discharge must terminate not more than 6 in. above the floor or to the exterior and must not be trapped.

Ohm's law: E = I × R; power: P (watts) = E × I; single-phase P = E × I × PF for reactive loads.

Three-phase power: P = 1.732 × E × I × PF; use 1.732 for balanced three-phase calculations.

Motor full-load current comes from NEC Tables 430.248 (single-phase) and 430.250 (three-phase); branch-circuit conductors sized at 125% of FLC.

Motor overload protection is sized separately from short-circuit and ground-fault protection; overloads protect the motor, breakers protect the conductors.

Conductor ampacity must be corrected for ambient temperature and adjusted for more than three current-carrying conductors in a raceway.

Equipment grounding conductor sizing follows NEC Table 250.122 and is based on the rating of the overcurrent device, not the conductor ampacity.

Voltage drop single-phase: VD = 2 × K × I × L / CM; three-phase uses 1.732 in place of 2. K = 12.9 for copper, 21.2 for aluminum.

GFCI protection is required in bathrooms, garages, outdoors, kitchens, and within 6 ft of sinks; AFCI is required for most 120-volt branch circuits in dwellings.

Disconnecting means for a motor must be within sight of the motor and controller, and a nameplate-rated horsepower switch must be used.

ORC Chapter 4740 governs Ohio's heating, ventilating, air conditioning, and refrigeration contractors; the Ohio Construction Industry Licensing Board (OCILB) administers licensing.

A license is required to advertise or contract for HVAC, refrigeration, plumbing, hydronics, or electrical work in Ohio; local jurisdictions may not require a separate license for work covered by a state license.

Applicants for the HVAC contractor license must document at least 5 years of business experience in the trade, or equivalent education and experience acceptable to the board.

Examination is required and passing scores are set by the board; a passing exam result remains valid for a limited period before the license must be issued.

Continuing education is required for renewal; the board sets the hours and content categories, and certificates of completion must be retained.

Contractors must maintain a surety bond and proof of liability insurance as a condition of licensure and renewal.

Responsible person: the licensed contractor must be actively engaged in and responsible for the work; the license is not transferable to another person or entity.

Unlicensed practice is subject to civil penalties and injunctive action by the board, and the board may suspend, revoke, or refuse to renew a license for violations.

License renewal and reinstatement deadlines, fees, and late penalties are set by the board in administrative rule; a lapsed license cannot be used to pull permits.

Sensible heat formula: Q (Btu/h) = 1.08 × CFM × ΔT for standard air at sea level; latent heat: Q = 0.68 × CFM × ΔW (grains/lb).

Total heat of air: Q = 4.5 × CFM × Δh, where h is enthalpy in Btu/lb of dry air.

Superheat = suction line temperature minus saturated suction temperature at measured suction pressure; target 8-12°F at evaporator outlet for TXV systems.

Subcooling = saturated condensing temperature minus liquid line temperature; a low subcooling with bubbles in the sight glass indicates undercharge.

Refrigerant glide exists in zeotropic blends (R-410A, R-407C); use dew point for superheat and bubble point for subcooling on the same blend.

Standard airflow rule: 400 CFM per ton nominal cooling; latent capacity drops sharply below about 350 CFM/ton.

Duct static budget: typical residential supply static 0.1 in. w.c., return 0.05 in. w.c.; total external static pressure commonly 0.5 in. w.c.

Combustion air: Category I appliances need 50 cu ft per 1,000 Btu/h input for unconfined spaces; two permanent openings sized 1 sq in. per 1,000 Btu/h each.

Refrigerant safety groups per ASHRAE 34: A1 (R-410A, R-134a) lower toxicity, no flame propagation; A2L (R-32, R-454B) lower flammability.

Water column pressure: 1 psi = 2.31 ft of head; pump head in feet divided by 2.31 gives psi.

Hydronic heat delivery: Q (Btu/h) = 500 × GPM × ΔT for water; 485 × GPM × ΔT for 30% glycol, 450 for 50% glycol.

BTU output of a boiler equals GPM × 500 × ΔT; a 20°F design ΔT is standard for residential baseboard loops.

Expansion tank sizing uses acceptance volume: bladder tanks sized from system volume, fill pressure, and maximum pressure; precharge equals fill pressure.

Relief valve setting must not exceed the working pressure rating of any component in the system; typical residential hydronic relief is 30 psi.

Backflow protection: an RPZ is required for high-hazard cross-connections; a double check valve assembly is allowed only for low hazard.

Fixture unit method per ASPE: 1 water closet = 2.5 WSFU, lavatory = 1 WSFU, bathtub = 4 WSFU; convert total WSFU to GPM using the Hunter curve.

Slope of horizontal drainage pipe less than 3 in. diameter is 1/4 in. per foot; 4 in. and larger may use 1/8 in. per foot.

Water heater T&P relief valve discharge must terminate not more than 6 in. above the floor or to the exterior and must not be trapped.

Ohm's law: E = I × R; power: P (watts) = E × I; single-phase P = E × I × PF for reactive loads.

Three-phase power: P = 1.732 × E × I × PF; use 1.732 for balanced three-phase calculations.

Motor full-load current comes from NEC Tables 430.248 (single-phase) and 430.250 (three-phase); branch-circuit conductors sized at 125% of FLC.

Motor overload protection is sized separately from short-circuit and ground-fault protection; overloads protect the motor, breakers protect the conductors.

Conductor ampacity must be corrected for ambient temperature and adjusted for more than three current-carrying conductors in a raceway.

Equipment grounding conductor sizing follows NEC Table 250.122 and is based on the rating of the overcurrent device, not the conductor ampacity.

Voltage drop single-phase: VD = 2 × K × I × L / CM; three-phase uses 1.732 in place of 2. K = 12.9 for copper, 21.2 for aluminum.

GFCI protection is required in bathrooms, garages, outdoors, kitchens, and within 6 ft of sinks; AFCI is required for most 120-volt branch circuits in dwellings.

Disconnecting means for a motor must be within sight of the motor and controller, and a nameplate-rated horsepower switch must be used.

ORC Chapter 4740 governs Ohio's heating, ventilating, air conditioning, and refrigeration contractors; the Ohio Construction Industry Licensing Board (OCILB) administers licensing.

A license is required to advertise or contract for HVAC, refrigeration, plumbing, hydronics, or electrical work in Ohio; local jurisdictions may not require a separate license for work covered by a state license.

Applicants for the HVAC contractor license must document at least 5 years of business experience in the trade, or equivalent education and experience acceptable to the board.

Examination is required and passing scores are set by the board; a passing exam result remains valid for a limited period before the license must be issued.

Continuing education is required for renewal; the board sets the hours and content categories, and certificates of completion must be retained.

Contractors must maintain a surety bond and proof of liability insurance as a condition of licensure and renewal.

Responsible person: the licensed contractor must be actively engaged in and responsible for the work; the license is not transferable to another person or entity.

Unlicensed practice is subject to civil penalties and injunctive action by the board, and the board may suspend, revoke, or refuse to renew a license for violations.

License renewal and reinstatement deadlines, fees, and late penalties are set by the board in administrative rule; a lapsed license cannot be used to pull permits.

Sensible heat formula: Q (Btu/h) = 1.08 × CFM × ΔT for standard air at sea level; latent heat: Q = 0.68 × CFM × ΔW (grains/lb).

Total heat of air: Q = 4.5 × CFM × Δh, where h is enthalpy in Btu/lb of dry air.

Superheat = suction line temperature minus saturated suction temperature at measured suction pressure; target 8-12°F at evaporator outlet for TXV systems.

Subcooling = saturated condensing temperature minus liquid line temperature; a low subcooling with bubbles in the sight glass indicates undercharge.

Refrigerant glide exists in zeotropic blends (R-410A, R-407C); use dew point for superheat and bubble point for subcooling on the same blend.

Standard airflow rule: 400 CFM per ton nominal cooling; latent capacity drops sharply below about 350 CFM/ton.

Duct static budget: typical residential supply static 0.1 in. w.c., return 0.05 in. w.c.; total external static pressure commonly 0.5 in. w.c.

Combustion air: Category I appliances need 50 cu ft per 1,000 Btu/h input for unconfined spaces; two permanent openings sized 1 sq in. per 1,000 Btu/h each.

Refrigerant safety groups per ASHRAE 34: A1 (R-410A, R-134a) lower toxicity, no flame propagation; A2L (R-32, R-454B) lower flammability.

Water column pressure: 1 psi = 2.31 ft of head; pump head in feet divided by 2.31 gives psi.

Hydronic heat delivery: Q (Btu/h) = 500 × GPM × ΔT for water; 485 × GPM × ΔT for 30% glycol, 450 for 50% glycol.

BTU output of a boiler equals GPM × 500 × ΔT; a 20°F design ΔT is standard for residential baseboard loops.

Expansion tank sizing uses acceptance volume: bladder tanks sized from system volume, fill pressure, and maximum pressure; precharge equals fill pressure.

Relief valve setting must not exceed the working pressure rating of any component in the system; typical residential hydronic relief is 30 psi.

Backflow protection: an RPZ is required for high-hazard cross-connections; a double check valve assembly is allowed only for low hazard.

Fixture unit method per ASPE: 1 water closet = 2.5 WSFU, lavatory = 1 WSFU, bathtub = 4 WSFU; convert total WSFU to GPM using the Hunter curve.

Slope of horizontal drainage pipe less than 3 in. diameter is 1/4 in. per foot; 4 in. and larger may use 1/8 in. per foot.

Water heater T&P relief valve discharge must terminate not more than 6 in. above the floor or to the exterior and must not be trapped.

Ohm's law: E = I × R; power: P (watts) = E × I; single-phase P = E × I × PF for reactive loads.

Three-phase power: P = 1.732 × E × I × PF; use 1.732 for balanced three-phase calculations.

Motor full-load current comes from NEC Tables 430.248 (single-phase) and 430.250 (three-phase); branch-circuit conductors sized at 125% of FLC.

Motor overload protection is sized separately from short-circuit and ground-fault protection; overloads protect the motor, breakers protect the conductors.

Conductor ampacity must be corrected for ambient temperature and adjusted for more than three current-carrying conductors in a raceway.

Equipment grounding conductor sizing follows NEC Table 250.122 and is based on the rating of the overcurrent device, not the conductor ampacity.

Voltage drop single-phase: VD = 2 × K × I × L / CM; three-phase uses 1.732 in place of 2. K = 12.9 for copper, 21.2 for aluminum.

GFCI protection is required in bathrooms, garages, outdoors, kitchens, and within 6 ft of sinks; AFCI is required for most 120-volt branch circuits in dwellings.

Disconnecting means for a motor must be within sight of the motor and controller, and a nameplate-rated horsepower switch must be used.

ORC Chapter 4740 governs Ohio's heating, ventilating, air conditioning, and refrigeration contractors; the Ohio Construction Industry Licensing Board (OCILB) administers licensing.

A license is required to advertise or contract for HVAC, refrigeration, plumbing, hydronics, or electrical work in Ohio; local jurisdictions may not require a separate license for work covered by a state license.

Applicants for the HVAC contractor license must document at least 5 years of business experience in the trade, or equivalent education and experience acceptable to the board.

Examination is required and passing scores are set by the board; a passing exam result remains valid for a limited period before the license must be issued.

Continuing education is required for renewal; the board sets the hours and content categories, and certificates of completion must be retained.

Contractors must maintain a surety bond and proof of liability insurance as a condition of licensure and renewal.

Responsible person: the licensed contractor must be actively engaged in and responsible for the work; the license is not transferable to another person or entity.

Unlicensed practice is subject to civil penalties and injunctive action by the board, and the board may suspend, revoke, or refuse to renew a license for violations.

License renewal and reinstatement deadlines, fees, and late penalties are set by the board in administrative rule; a lapsed license cannot be used to pull permits.

Sensible heat formula: Q (Btu/h) = 1.08 × CFM × ΔT for standard air at sea level; latent heat: Q = 0.68 × CFM × ΔW (grains/lb).

Total heat of air: Q = 4.5 × CFM × Δh, where h is enthalpy in Btu/lb of dry air.

Superheat = suction line temperature minus saturated suction temperature at measured suction pressure; target 8-12°F at evaporator outlet for TXV systems.

Subcooling = saturated condensing temperature minus liquid line temperature; a low subcooling with bubbles in the sight glass indicates undercharge.

Refrigerant glide exists in zeotropic blends (R-410A, R-407C); use dew point for superheat and bubble point for subcooling on the same blend.

Standard airflow rule: 400 CFM per ton nominal cooling; latent capacity drops sharply below about 350 CFM/ton.

Duct static budget: typical residential supply static 0.1 in. w.c., return 0.05 in. w.c.; total external static pressure commonly 0.5 in. w.c.

Combustion air: Category I appliances need 50 cu ft per 1,000 Btu/h input for unconfined spaces; two permanent openings sized 1 sq in. per 1,000 Btu/h each.

Refrigerant safety groups per ASHRAE 34: A1 (R-410A, R-134a) lower toxicity, no flame propagation; A2L (R-32, R-454B) lower flammability.

Water column pressure: 1 psi = 2.31 ft of head; pump head in feet divided by 2.31 gives psi.

Hydronic heat delivery: Q (Btu/h) = 500 × GPM × ΔT for water; 485 × GPM × ΔT for 30% glycol, 450 for 50% glycol.

BTU output of a boiler equals GPM × 500 × ΔT; a 20°F design ΔT is standard for residential baseboard loops.

Expansion tank sizing uses acceptance volume: bladder tanks sized from system volume, fill pressure, and maximum pressure; precharge equals fill pressure.

Relief valve setting must not exceed the working pressure rating of any component in the system; typical residential hydronic relief is 30 psi.

Backflow protection: an RPZ is required for high-hazard cross-connections; a double check valve assembly is allowed only for low hazard.

Fixture unit method per ASPE: 1 water closet = 2.5 WSFU, lavatory = 1 WSFU, bathtub = 4 WSFU; convert total WSFU to GPM using the Hunter curve.

Slope of horizontal drainage pipe less than 3 in. diameter is 1/4 in. per foot; 4 in. and larger may use 1/8 in. per foot.

Water heater T&P relief valve discharge must terminate not more than 6 in. above the floor or to the exterior and must not be trapped.

Ohm's law: E = I × R; power: P (watts) = E × I; single-phase P = E × I × PF for reactive loads.

Three-phase power: P = 1.732 × E × I × PF; use 1.732 for balanced three-phase calculations.

Motor full-load current comes from NEC Tables 430.248 (single-phase) and 430.250 (three-phase); branch-circuit conductors sized at 125% of FLC.

Motor overload protection is sized separately from short-circuit and ground-fault protection; overloads protect the motor, breakers protect the conductors.

Conductor ampacity must be corrected for ambient temperature and adjusted for more than three current-carrying conductors in a raceway.

Equipment grounding conductor sizing follows NEC Table 250.122 and is based on the rating of the overcurrent device, not the conductor ampacity.

Voltage drop single-phase: VD = 2 × K × I × L / CM; three-phase uses 1.732 in place of 2. K = 12.9 for copper, 21.2 for aluminum.

GFCI protection is required in bathrooms, garages, outdoors, kitchens, and within 6 ft of sinks; AFCI is required for most 120-volt branch circuits in dwellings.

Disconnecting means for a motor must be within sight of the motor and controller, and a nameplate-rated horsepower switch must be used.

ORC Chapter 4740 governs Ohio's heating, ventilating, air conditioning, and refrigeration contractors; the Ohio Construction Industry Licensing Board (OCILB) administers licensing.

A license is required to advertise or contract for HVAC, refrigeration, plumbing, hydronics, or electrical work in Ohio; local jurisdictions may not require a separate license for work covered by a state license.

Applicants for the HVAC contractor license must document at least 5 years of business experience in the trade, or equivalent education and experience acceptable to the board.

Examination is required and passing scores are set by the board; a passing exam result remains valid for a limited period before the license must be issued.

Continuing education is required for renewal; the board sets the hours and content categories, and certificates of completion must be retained.

Contractors must maintain a surety bond and proof of liability insurance as a condition of licensure and renewal.

Responsible person: the licensed contractor must be actively engaged in and responsible for the work; the license is not transferable to another person or entity.

Unlicensed practice is subject to civil penalties and injunctive action by the board, and the board may suspend, revoke, or refuse to renew a license for violations.

License renewal and reinstatement deadlines, fees, and late penalties are set by the board in administrative rule; a lapsed license cannot be used to pull permits.

Sensible heat formula: Q (Btu/h) = 1.08 × CFM × ΔT for standard air at sea level; latent heat: Q = 0.68 × CFM × ΔW (grains/lb).

Total heat of air: Q = 4.5 × CFM × Δh, where h is enthalpy in Btu/lb of dry air.

Superheat = suction line temperature minus saturated suction temperature at measured suction pressure; target 8-12°F at evaporator outlet for TXV systems.

Subcooling = saturated condensing temperature minus liquid line temperature; a low subcooling with bubbles in the sight glass indicates undercharge.

Refrigerant glide exists in zeotropic blends (R-410A, R-407C); use dew point for superheat and bubble point for subcooling on the same blend.

Standard airflow rule: 400 CFM per ton nominal cooling; latent capacity drops sharply below about 350 CFM/ton.

Duct static budget: typical residential supply static 0.1 in. w.c., return 0.05 in. w.c.; total external static pressure commonly 0.5 in. w.c.

Combustion air: Category I appliances need 50 cu ft per 1,000 Btu/h input for unconfined spaces; two permanent openings sized 1 sq in. per 1,000 Btu/h each.

Refrigerant safety groups per ASHRAE 34: A1 (R-410A, R-134a) lower toxicity, no flame propagation; A2L (R-32, R-454B) lower flammability.

Water column pressure: 1 psi = 2.31 ft of head; pump head in feet divided by 2.31 gives psi.

Hydronic heat delivery: Q (Btu/h) = 500 × GPM × ΔT for water; 485 × GPM × ΔT for 30% glycol, 450 for 50% glycol.

BTU output of a boiler equals GPM × 500 × ΔT; a 20°F design ΔT is standard for residential baseboard loops.

Expansion tank sizing uses acceptance volume: bladder tanks sized from system volume, fill pressure, and maximum pressure; precharge equals fill pressure.

Relief valve setting must not exceed the working pressure rating of any component in the system; typical residential hydronic relief is 30 psi.

Backflow protection: an RPZ is required for high-hazard cross-connections; a double check valve assembly is allowed only for low hazard.

Fixture unit method per ASPE: 1 water closet = 2.5 WSFU, lavatory = 1 WSFU, bathtub = 4 WSFU; convert total WSFU to GPM using the Hunter curve.

Slope of horizontal drainage pipe less than 3 in. diameter is 1/4 in. per foot; 4 in. and larger may use 1/8 in. per foot.

Water heater T&P relief valve discharge must terminate not more than 6 in. above the floor or to the exterior and must not be trapped.

Ohm's law: E = I × R; power: P (watts) = E × I; single-phase P = E × I × PF for reactive loads.

Three-phase power: P = 1.732 × E × I × PF; use 1.732 for balanced three-phase calculations.

Motor full-load current comes from NEC Tables 430.248 (single-phase) and 430.250 (three-phase); branch-circuit conductors sized at 125% of FLC.

Motor overload protection is sized separately from short-circuit and ground-fault protection; overloads protect the motor, breakers protect the conductors.

Conductor ampacity must be corrected for ambient temperature and adjusted for more than three current-carrying conductors in a raceway.

Equipment grounding conductor sizing follows NEC Table 250.122 and is based on the rating of the overcurrent device, not the conductor ampacity.

Voltage drop single-phase: VD = 2 × K × I × L / CM; three-phase uses 1.732 in place of 2. K = 12.9 for copper, 21.2 for aluminum.

GFCI protection is required in bathrooms, garages, outdoors, kitchens, and within 6 ft of sinks; AFCI is required for most 120-volt branch circuits in dwellings.

Disconnecting means for a motor must be within sight of the motor and controller, and a nameplate-rated horsepower switch must be used.

ORC Chapter 4740 governs Ohio's heating, ventilating, air conditioning, and refrigeration contractors; the Ohio Construction Industry Licensing Board (OCILB) administers licensing.

A license is required to advertise or contract for HVAC, refrigeration, plumbing, hydronics, or electrical work in Ohio; local jurisdictions may not require a separate license for work covered by a state license.

Applicants for the HVAC contractor license must document at least 5 years of business experience in the trade, or equivalent education and experience acceptable to the board.

Examination is required and passing scores are set by the board; a passing exam result remains valid for a limited period before the license must be issued.

Continuing education is required for renewal; the board sets the hours and content categories, and certificates of completion must be retained.

Contractors must maintain a surety bond and proof of liability insurance as a condition of licensure and renewal.

Responsible person: the licensed contractor must be actively engaged in and responsible for the work; the license is not transferable to another person or entity.

Unlicensed practice is subject to civil penalties and injunctive action by the board, and the board may suspend, revoke, or refuse to renew a license for violations.

License renewal and reinstatement deadlines, fees, and late penalties are set by the board in administrative rule; a lapsed license cannot be used to pull permits.

Sensible heat formula: Q (Btu/h) = 1.08 × CFM × ΔT for standard air at sea level; latent heat: Q = 0.68 × CFM × ΔW (grains/lb).

Total heat of air: Q = 4.5 × CFM × Δh, where h is enthalpy in Btu/lb of dry air.

Superheat = suction line temperature minus saturated suction temperature at measured suction pressure; target 8-12°F at evaporator outlet for TXV systems.

Subcooling = saturated condensing temperature minus liquid line temperature; a low subcooling with bubbles in the sight glass indicates undercharge.

Refrigerant glide exists in zeotropic blends (R-410A, R-407C); use dew point for superheat and bubble point for subcooling on the same blend.

Standard airflow rule: 400 CFM per ton nominal cooling; latent capacity drops sharply below about 350 CFM/ton.

Duct static budget: typical residential supply static 0.1 in. w.c., return 0.05 in. w.c.; total external static pressure commonly 0.5 in. w.c.

Combustion air: Category I appliances need 50 cu ft per 1,000 Btu/h input for unconfined spaces; two permanent openings sized 1 sq in. per 1,000 Btu/h each.

Refrigerant safety groups per ASHRAE 34: A1 (R-410A, R-134a) lower toxicity, no flame propagation; A2L (R-32, R-454B) lower flammability.

Water column pressure: 1 psi = 2.31 ft of head; pump head in feet divided by 2.31 gives psi.

Hydronic heat delivery: Q (Btu/h) = 500 × GPM × ΔT for water; 485 × GPM × ΔT for 30% glycol, 450 for 50% glycol.

BTU output of a boiler equals GPM × 500 × ΔT; a 20°F design ΔT is standard for residential baseboard loops.

Expansion tank sizing uses acceptance volume: bladder tanks sized from system volume, fill pressure, and maximum pressure; precharge equals fill pressure.

Relief valve setting must not exceed the working pressure rating of any component in the system; typical residential hydronic relief is 30 psi.

Backflow protection: an RPZ is required for high-hazard cross-connections; a double check valve assembly is allowed only for low hazard.

Fixture unit method per ASPE: 1 water closet = 2.5 WSFU, lavatory = 1 WSFU, bathtub = 4 WSFU; convert total WSFU to GPM using the Hunter curve.

Slope of horizontal drainage pipe less than 3 in. diameter is 1/4 in. per foot; 4 in. and larger may use 1/8 in. per foot.

Water heater T&P relief valve discharge must terminate not more than 6 in. above the floor or to the exterior and must not be trapped.

Ohm's law: E = I × R; power: P (watts) = E × I; single-phase P = E × I × PF for reactive loads.

Three-phase power: P = 1.732 × E × I × PF; use 1.732 for balanced three-phase calculations.

Motor full-load current comes from NEC Tables 430.248 (single-phase) and 430.250 (three-phase); branch-circuit conductors sized at 125% of FLC.

Motor overload protection is sized separately from short-circuit and ground-fault protection; overloads protect the motor, breakers protect the conductors.

Conductor ampacity must be corrected for ambient temperature and adjusted for more than three current-carrying conductors in a raceway.

Equipment grounding conductor sizing follows NEC Table 250.122 and is based on the rating of the overcurrent device, not the conductor ampacity.

Voltage drop single-phase: VD = 2 × K × I × L / CM; three-phase uses 1.732 in place of 2. K = 12.9 for copper, 21.2 for aluminum.

GFCI protection is required in bathrooms, garages, outdoors, kitchens, and within 6 ft of sinks; AFCI is required for most 120-volt branch circuits in dwellings.

Disconnecting means for a motor must be within sight of the motor and controller, and a nameplate-rated horsepower switch must be used.

ORC Chapter 4740 governs Ohio's heating, ventilating, air conditioning, and refrigeration contractors; the Ohio Construction Industry Licensing Board (OCILB) administers licensing.

A license is required to advertise or contract for HVAC, refrigeration, plumbing, hydronics, or electrical work in Ohio; local jurisdictions may not require a separate license for work covered by a state license.

Applicants for the HVAC contractor license must document at least 5 years of business experience in the trade, or equivalent education and experience acceptable to the board.

Examination is required and passing scores are set by the board; a passing exam result remains valid for a limited period before the license must be issued.

Continuing education is required for renewal; the board sets the hours and content categories, and certificates of completion must be retained.

Contractors must maintain a surety bond and proof of liability insurance as a condition of licensure and renewal.

Responsible person: the licensed contractor must be actively engaged in and responsible for the work; the license is not transferable to another person or entity.

Unlicensed practice is subject to civil penalties and injunctive action by the board, and the board may suspend, revoke, or refuse to renew a license for violations.

License renewal and reinstatement deadlines, fees, and late penalties are set by the board in administrative rule; a lapsed license cannot be used to pull permits.

Sensible heat formula: Q (Btu/h) = 1.08 × CFM × ΔT for standard air at sea level; latent heat: Q = 0.68 × CFM × ΔW (grains/lb).

Total heat of air: Q = 4.5 × CFM × Δh, where h is enthalpy in Btu/lb of dry air.

Superheat = suction line temperature minus saturated suction temperature at measured suction pressure; target 8-12°F at evaporator outlet for TXV systems.

Subcooling = saturated condensing temperature minus liquid line temperature; a low subcooling with bubbles in the sight glass indicates undercharge.

Refrigerant glide exists in zeotropic blends (R-410A, R-407C); use dew point for superheat and bubble point for subcooling on the same blend.

Standard airflow rule: 400 CFM per ton nominal cooling; latent capacity drops sharply below about 350 CFM/ton.

Duct static budget: typical residential supply static 0.1 in. w.c., return 0.05 in. w.c.; total external static pressure commonly 0.5 in. w.c.

Combustion air: Category I appliances need 50 cu ft per 1,000 Btu/h input for unconfined spaces; two permanent openings sized 1 sq in. per 1,000 Btu/h each.

Refrigerant safety groups per ASHRAE 34: A1 (R-410A, R-134a) lower toxicity, no flame propagation; A2L (R-32, R-454B) lower flammability.

Water column pressure: 1 psi = 2.31 ft of head; pump head in feet divided by 2.31 gives psi.

Hydronic heat delivery: Q (Btu/h) = 500 × GPM × ΔT for water; 485 × GPM × ΔT for 30% glycol, 450 for 50% glycol.

BTU output of a boiler equals GPM × 500 × ΔT; a 20°F design ΔT is standard for residential baseboard loops.

Expansion tank sizing uses acceptance volume: bladder tanks sized from system volume, fill pressure, and maximum pressure; precharge equals fill pressure.

Relief valve setting must not exceed the working pressure rating of any component in the system; typical residential hydronic relief is 30 psi.

Backflow protection: an RPZ is required for high-hazard cross-connections; a double check valve assembly is allowed only for low hazard.

Fixture unit method per ASPE: 1 water closet = 2.5 WSFU, lavatory = 1 WSFU, bathtub = 4 WSFU; convert total WSFU to GPM using the Hunter curve.

Slope of horizontal drainage pipe less than 3 in. diameter is 1/4 in. per foot; 4 in. and larger may use 1/8 in. per foot.

Water heater T&P relief valve discharge must terminate not more than 6 in. above the floor or to the exterior and must not be trapped.

Ohm's law: E = I × R; power: P (watts) = E × I; single-phase P = E × I × PF for reactive loads.

Three-phase power: P = 1.732 × E × I × PF; use 1.732 for balanced three-phase calculations.

Motor full-load current comes from NEC Tables 430.248 (single-phase) and 430.250 (three-phase); branch-circuit conductors sized at 125% of FLC.

Motor overload protection is sized separately from short-circuit and ground-fault protection; overloads protect the motor, breakers protect the conductors.

Conductor ampacity must be corrected for ambient temperature and adjusted for more than three current-carrying conductors in a raceway.

Equipment grounding conductor sizing follows NEC Table 250.122 and is based on the rating of the overcurrent device, not the conductor ampacity.

Voltage drop single-phase: VD = 2 × K × I × L / CM; three-phase uses 1.732 in place of 2. K = 12.9 for copper, 21.2 for aluminum.

GFCI protection is required in bathrooms, garages, outdoors, kitchens, and within 6 ft of sinks; AFCI is required for most 120-volt branch circuits in dwellings.

Disconnecting means for a motor must be within sight of the motor and controller, and a nameplate-rated horsepower switch must be used.

ORC Chapter 4740 governs Ohio's heating, ventilating, air conditioning, and refrigeration contractors; the Ohio Construction Industry Licensing Board (OCILB) administers licensing.

A license is required to advertise or contract for HVAC, refrigeration, plumbing, hydronics, or electrical work in Ohio; local jurisdictions may not require a separate license for work covered by a state license.

Applicants for the HVAC contractor license must document at least 5 years of business experience in the trade, or equivalent education and experience acceptable to the board.

Examination is required and passing scores are set by the board; a passing exam result remains valid for a limited period before the license must be issued.

Continuing education is required for renewal; the board sets the hours and content categories, and certificates of completion must be retained.

Contractors must maintain a surety bond and proof of liability insurance as a condition of licensure and renewal.

Responsible person: the licensed contractor must be actively engaged in and responsible for the work; the license is not transferable to another person or entity.

Unlicensed practice is subject to civil penalties and injunctive action by the board, and the board may suspend, revoke, or refuse to renew a license for violations.

License renewal and reinstatement deadlines, fees, and late penalties are set by the board in administrative rule; a lapsed license cannot be used to pull permits.