ICC M1 Residential Mechanical Inspector Exam
2026 | Actual Exam Prep + Verified Answers
Bundle
1. What is the minimum required clearance between a gas-fired furnace and combustible
material unless listed otherwise?
A. 0 inches
B. 1 inch
C. 6 inches
D. 12 inches
Answer: C. 6 inches
Clearances are typically specified by manufacturer, but 6 inches is a common default
minimum when not listed.
2. What type of vent is required for Category IV appliances?
A. Type B vent
B. Masonry chimney
C. Plastic vent
D. Single-wall metal vent
Answer: C. Plastic vent
Category IV appliances are condensing and require corrosion-resistant vent materials like
PVC.
3. What is the minimum slope for horizontal drainage piping?
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
Answer: C. 1/4 inch per foot
This ensures proper flow and prevents solids from settling in the pipe.
4. Combustion air can be supplied from indoors when the volume is at least how many
cubic feet per 1,000 BTU/hr?
A. 25
B. 50
C. 75
D. 100
Answer: B. 50
The code requires 50 cubic feet per 1,000 BTU/hr for indoor combustion air.
5. What is the minimum thickness of metal duct for a dryer exhaust?
A. 0.010 inch
B. 0.015 inch
C. 0.016 inch
D. 0.020 inch
Answer: B. 0.015 inch
Dryer ducts must be rigid and smooth with minimum thickness for safety and durability.
,6. What is the maximum length of a dryer exhaust duct without a booster fan?
A. 25 feet
B. 35 feet
C. 50 feet
D. 75 feet
Answer: A. 25 feet
The standard maximum length is 25 feet, adjusted for fittings.
7. What is the minimum required clearance for a chimney from combustible framing?
A. 1 inch
B. 2 inches
C. 3 inches
D. 4 inches
Answer: B. 2 inches
Masonry chimneys typically require a 2-inch air space clearance.
8. What is the primary purpose of a draft hood?
A. Increase efficiency
B. Control combustion air
C. Prevent downdrafts
D. Stabilize draft
Answer: D. Stabilize draft
Draft hoods regulate airflow and prevent excessive draft affecting combustion.
9. What type of system uses refrigerant to transfer heat?
A. Hydronic system
B. Forced air system
C. Vapor compression system
D. Radiant system
Answer: C. Vapor compression system
This is the standard refrigeration cycle used in HVAC systems.
10. What is the minimum R-value for duct insulation in unconditioned spaces?
A. R-4
B. R-6
C. R-8
D. R-10
Answer: C. R-8
Energy codes commonly require R-8 insulation in unconditioned areas.
11. What is the purpose of a condensate trap?
A. Increase airflow
B. Prevent gas leakage
C. Drain condensation
D. Prevent air leakage
Answer: D. Prevent air leakage
It blocks air movement while allowing condensate drainage.
12. What is the maximum temperature for a water heater thermostat?
A. 100°F
B. 120°F
C. 140°F
, D. 160°F
Answer: C. 140°F
Many codes limit thermostats to 140°F to prevent scalding.
13. What is required for appliances located in attics?
A. Lighting only
B. Flooring only
C. Access and service space
D. No requirements
Answer: C. Access and service space
Safe access and working clearance are required for maintenance.
14. What is the minimum size of combustion air openings?
A. 1 sq in per 1,000 BTU
B. 1 sq in per 2,000 BTU
C. 1 sq in per 4,000 BTU
D. 1 sq in per 5,000 BTU
Answer: C. 1 sq in per 4,000 BTU
This applies when air is taken from indoors.
15. What type of joint is required for gas piping?
A. Welded
B. Threaded
C. Glued
D. Press-fit only
Answer: B. Threaded
Steel gas piping typically uses threaded fittings.
16. What is the purpose of a backdraft damper?
A. Increase airflow
B. Prevent reverse airflow
C. Improve efficiency
D. Reduce noise
Answer: B. Prevent reverse airflow
It ensures air flows in only one direction.
17. What is the required slope for horizontal vent connectors?
A. Downward
B. Level
C. Upward 1/4 inch per foot
D. Upward 1/2 inch per foot
Answer: C. Upward 1/4 inch per foot
This helps exhaust gases flow properly.
18. What material is prohibited for dryer ducts?
A. Aluminum
B. Galvanized steel
C. Flexible plastic
D. Stainless steel
Answer: C. Flexible plastic
Plastic ducts pose a fire hazard and are not allowed.
2026 | Actual Exam Prep + Verified Answers
Bundle
1. What is the minimum required clearance between a gas-fired furnace and combustible
material unless listed otherwise?
A. 0 inches
B. 1 inch
C. 6 inches
D. 12 inches
Answer: C. 6 inches
Clearances are typically specified by manufacturer, but 6 inches is a common default
minimum when not listed.
2. What type of vent is required for Category IV appliances?
A. Type B vent
B. Masonry chimney
C. Plastic vent
D. Single-wall metal vent
Answer: C. Plastic vent
Category IV appliances are condensing and require corrosion-resistant vent materials like
PVC.
3. What is the minimum slope for horizontal drainage piping?
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
Answer: C. 1/4 inch per foot
This ensures proper flow and prevents solids from settling in the pipe.
4. Combustion air can be supplied from indoors when the volume is at least how many
cubic feet per 1,000 BTU/hr?
A. 25
B. 50
C. 75
D. 100
Answer: B. 50
The code requires 50 cubic feet per 1,000 BTU/hr for indoor combustion air.
5. What is the minimum thickness of metal duct for a dryer exhaust?
A. 0.010 inch
B. 0.015 inch
C. 0.016 inch
D. 0.020 inch
Answer: B. 0.015 inch
Dryer ducts must be rigid and smooth with minimum thickness for safety and durability.
,6. What is the maximum length of a dryer exhaust duct without a booster fan?
A. 25 feet
B. 35 feet
C. 50 feet
D. 75 feet
Answer: A. 25 feet
The standard maximum length is 25 feet, adjusted for fittings.
7. What is the minimum required clearance for a chimney from combustible framing?
A. 1 inch
B. 2 inches
C. 3 inches
D. 4 inches
Answer: B. 2 inches
Masonry chimneys typically require a 2-inch air space clearance.
8. What is the primary purpose of a draft hood?
A. Increase efficiency
B. Control combustion air
C. Prevent downdrafts
D. Stabilize draft
Answer: D. Stabilize draft
Draft hoods regulate airflow and prevent excessive draft affecting combustion.
9. What type of system uses refrigerant to transfer heat?
A. Hydronic system
B. Forced air system
C. Vapor compression system
D. Radiant system
Answer: C. Vapor compression system
This is the standard refrigeration cycle used in HVAC systems.
10. What is the minimum R-value for duct insulation in unconditioned spaces?
A. R-4
B. R-6
C. R-8
D. R-10
Answer: C. R-8
Energy codes commonly require R-8 insulation in unconditioned areas.
11. What is the purpose of a condensate trap?
A. Increase airflow
B. Prevent gas leakage
C. Drain condensation
D. Prevent air leakage
Answer: D. Prevent air leakage
It blocks air movement while allowing condensate drainage.
12. What is the maximum temperature for a water heater thermostat?
A. 100°F
B. 120°F
C. 140°F
, D. 160°F
Answer: C. 140°F
Many codes limit thermostats to 140°F to prevent scalding.
13. What is required for appliances located in attics?
A. Lighting only
B. Flooring only
C. Access and service space
D. No requirements
Answer: C. Access and service space
Safe access and working clearance are required for maintenance.
14. What is the minimum size of combustion air openings?
A. 1 sq in per 1,000 BTU
B. 1 sq in per 2,000 BTU
C. 1 sq in per 4,000 BTU
D. 1 sq in per 5,000 BTU
Answer: C. 1 sq in per 4,000 BTU
This applies when air is taken from indoors.
15. What type of joint is required for gas piping?
A. Welded
B. Threaded
C. Glued
D. Press-fit only
Answer: B. Threaded
Steel gas piping typically uses threaded fittings.
16. What is the purpose of a backdraft damper?
A. Increase airflow
B. Prevent reverse airflow
C. Improve efficiency
D. Reduce noise
Answer: B. Prevent reverse airflow
It ensures air flows in only one direction.
17. What is the required slope for horizontal vent connectors?
A. Downward
B. Level
C. Upward 1/4 inch per foot
D. Upward 1/2 inch per foot
Answer: C. Upward 1/4 inch per foot
This helps exhaust gases flow properly.
18. What material is prohibited for dryer ducts?
A. Aluminum
B. Galvanized steel
C. Flexible plastic
D. Stainless steel
Answer: C. Flexible plastic
Plastic ducts pose a fire hazard and are not allowed.
