12.2 Appliance Clearances to Combustibles, Access & Location Limits
Key Takeaways
- IFGC 2018 Table 308.2 takes an 18-inch side and rear clearance down to 6 inches with 24-gage sheet metal on a ventilated airspace, and to 9 inches above the appliance.
- IFGC 306.1 requires a level working space not less than 30 inches deep by 30 inches wide in front of the control side of every appliance.
- IFGC 303.3 bars appliances from sleeping rooms, bathrooms, toilet rooms, storage closets and surgical rooms except under six listed exceptions, including direct-vent units.
- A domestic dryer exhaust duct is limited to 35 feet, less 5 feet for each 4-inch radius mitered 90-degree elbow and 2 feet 6 inches for each mitered 45 (Table 614.8.4.1).
- IFGC 614.4 forbids screens at the dryer termination and prohibits connecting a dryer exhaust duct to any vent connector, vent or chimney.
12.2 Appliance Clearances to Combustibles, Access & Location Limits
Quick Answer: IFGC 2018 Section 303.3 prohibits appliances in sleeping rooms, bathrooms, toilet rooms, storage closets and surgical rooms -- or in any space that opens only into such rooms -- unless one of six specific exceptions applies. The first and broadest is a direct-vent appliance installed in accordance with its listing and the manufacturer's instructions.
Clearance and location questions are the easiest points in the 40-question Gas Appliances and Piping domain because the answers are tabulated. The trap is that two different rules are in play: clearance to combustibles, which protects the building from the appliance, and access and working space, which protects the technician's ability to service it.
Listed Clearances Versus Reduced Clearances
IFGC 305.8 sets the baseline: heat-producing appliances maintain the clearances specified in the listing and the manufacturer's instructions, and those clearances "shall be reduced only in accordance with Section 308." The same section warns that clearance means real, permanent clearance -- it must account for door swing, drawer pull, overhead projections or shelving, and window swing, and door stops, limits and closers may not be used to create the required clearance.
Section 308 offers exactly two legal ways to reduce a clearance:
- A reduced clearance protective assembly listed and labeled to UL 1618, installed per its listing; or
- One of the eight forms of protection in Table 308.2, which is a lookup, not a percentage you calculate.
Where a needed distance is not printed in the table you may interpolate between the listed distances, but you may never extrapolate below the range of the table. And no reduction is permitted at all where the appliance or equipment listing specifically prohibits it.
Table 308.2 -- Selected Values (2018 IFGC)
Column 1 is the clearance above the appliance or a horizontal connector; column 2 is the clearance from the sides and rear, a vertical connector and single-wall metal pipe.
| Form of protection applied to the combustible material | 36 in required: above / sides | 18 in required: above / sides | 12 in required: above / sides |
|---|---|---|---|
| 3-1/2 in masonry wall, no ventilated airspace | -- / 24 | -- / 12 | -- / 9 |
| 1/2 in insulation board over 1 in glass fiber or mineral wool batts | 24 / 18 | 12 / 9 | 9 / 6 |
| 24-gage sheet metal with ventilated airspace | 18 / 12 | 9 / 6 | 6 / 4 |
| 1/2 in insulation board with ventilated airspace | 18 / 12 | 9 / 6 | 6 / 4 |
The footnotes carry the installation principle, and they are examinable:
- Air gap: a wall protector mounted on a flat wall away from corners needs a minimum 1-inch air gap, with the bottom and top edges, or the side and top edges, or all edges left open so air can circulate. Keep not less than 1 inch between the protection system and the combustible wall or ceiling.
- Spacers and ties must be noncombustible, and no spacer or tie may be placed directly opposite the appliance or connector -- that would be a straight conduction path into the framing.
- Not less than 1 inch must remain between the appliance and the protector.
- Clearance is measured from the outer surface of the combustible material to the nearest point on the appliance, disregarding the protection applied to it.
- Mineral wool batts need a minimum density of 8 pounds per cubic foot and a melting point of 1,500 degrees F; insulation used in the assembly must have a thermal conductivity of 1.0 Btu-in/ft2-h-degree F or less.
- No reduction may interfere with combustion air, draft hood clearance and relief, or accessibility for servicing.
Worked example. An appliance is listed for 18 inches to combustibles at the sides and rear. You install 24-gage sheet metal on a 1-inch ventilated airspace, extended far enough in each direction that the protected zone equals the unprotected clearance (Figure 308.2(1)). Table 308.2 gives 6 inches -- a reduction of 12 inches, or 12/18 = 67 percent. Above the appliance the same protection takes 18 inches down to 9 inches, only 50 percent, which is why you must read the correct column instead of applying one percentage everywhere.
A listed appliance requires 18 inches of clearance to combustible material at the sides and rear. The installer applies 24-gage sheet metal over a 1-inch ventilated airspace on the wall. Under IFGC 2018 Table 308.2, what is the reduced side and rear clearance?
Access and Working Space
IFGC 306.1 requires appliances, control devices and heat exchangers to be accessible for inspection, service, repair and replacement without disabling a fire-resistance-rated assembly and without removing permanent construction, other appliances, or piping and ducts not connected to the unit being worked on. A level working space not less than 30 inches deep and 30 inches wide must be provided in front of the control side. IPC 502.5 repeats the same 30-inch by 30-inch rule for water heaters.
Getting to that space has its own dimensions. Rooms containing appliances need a door and unobstructed passageway not less than 36 inches wide and 80 inches high (306.2). Inside a dwelling unit, an appliance in a compartment, alcove, basement or similar space may be reached through an opening or door and a passageway not less than 24 inches wide and large enough to remove the largest appliance, provided the 30-inch-deep service space -- at least the height of the appliance, but never less than 30 inches -- exists with the door open.
Prohibited Locations and the Six Exceptions (303.3)
Learn the exception list, because exam items are usually written as "which installation is permitted."
| # | Permitted despite the prohibition |
|---|---|
| 1 | A direct-vent appliance installed per its listing and instructions |
| 2 | Vented room heaters, wall furnaces, vented decorative appliances, vented gas fireplaces and fireplace heaters in rooms meeting the volume criteria of Section 304.5 |
| 3 | One wall-mounted unvented room heater in a bathroom, equipped per Section 621.6, input not greater than 6,000 Btu/h |
| 4 | One wall-mounted unvented room heater in a bedroom, equipped per Section 621.6, input not greater than 10,000 Btu/h |
| 5 | An appliance in a space opening only into a bedroom or bathroom, used for no other purpose, with a solid weather-stripped door and approved self-closing device, and combustion air taken directly from the outdoors per 304.6 |
| 6 | A clothes dryer in a residential bathroom or toilet room with a permanent opening of not less than 100 square inches communicating with a space outside a sleeping room, bathroom, toilet room or storage closet |
Section 621.6 is the oxygen-depletion safety system (ODS) that shuts an unvented heater off as room oxygen falls -- exceptions 3 and 4 depend on it. Also note IFGC 303.5: furnaces and boilers installed in closets and alcoves must be listed for that installation.
Garages, Floors and Cooking Tops
Beyond the 18-inch ignition-source rule, three floor-related clearances get tested:
- 305.7 -- clearance from grade: an appliance at grade level sits on a level concrete slab or other approved material extending not less than 3 inches above adjoining grade, or is suspended not less than 6 inches above grade.
- 620.4 -- combustible floors: floor-mounted unit heaters shall not be installed on combustible floors unless listed for such installation. Suspended unit heaters carry 18 inches at the sides, 12 inches at the bottom and 6 inches above the top with an internal draft hood.
- 623.4 and 623.7 -- cooking appliances: domestic ranges on combustible floors sit on their own bases or legs at the label clearances, and household cooking appliances need not less than 30 inches of vertical clearance above the cooking top to combustible material and metal cabinets. That drops to 24 inches only where the underside is protected with 1/4-inch insulating millboard covered by 0.0122-inch sheet metal, a metal ventilating hood is installed, or a listed appliance or microwave is mounted above per its instructions.
Under IFGC 2018 Section 303.3, which appliance installation is permitted in a bedroom?
Clothes Dryer Exhaust (IFGC Section 614)
A gas dryer is a fuel-burning appliance whose exhaust carries both moisture and products of combustion, so the duct rules are strict.
- 614.1: the exhaust system is independent of all other systems and discharges to the outside.
- 614.4: the duct terminates outdoors with a backdraft damper; screens shall not be installed at the termination; ducts shall not be connected or installed with sheet metal screws or other fasteners that obstruct flow; and a dryer exhaust duct shall not be connected to a vent connector, vent or chimney, nor extend into or through ducts or plenums. The terminal passageway must be undiminished with an open area of not less than 12.5 square inches (614.4.1).
- 614.8.1 and 614.8.2: the duct has a smooth interior, is metal not less than 0.016 inch thick and 4 inches nominal in diameter, is supported at 4-foot intervals, is assembled with the insert end pointing in the direction of airflow, and is never joined with fasteners protruding more than 1/8 inch into the inside of the duct. A screw point in the airstream is a lint hook.
- 614.8.3: the transition duct is a single length listed to UL 2158A, not more than 8 feet long, and not concealed within construction.
- 614.6: installations exhausting more than 200 cfm need makeup air, and a closet designed for a dryer needs an opening of not less than 100 square inches.
The 35-Foot Rule and Fitting Deductions
614.8.4.1 sets the maximum exhaust duct length at 35 feet, measured from the connection to the transition duct to the outlet terminal. Fittings are then deducted using Table 614.8.4.1:
| Fitting | Equivalent length |
|---|---|
| 4-inch radius mitered 45-degree elbow | 2 ft 6 in |
| 4-inch radius mitered 90-degree elbow | 5 ft |
| 6-inch radius smooth 45-degree elbow | 1 ft |
| 6-inch radius smooth 90-degree elbow | 1 ft 9 in |
| 8-inch radius smooth 45-degree elbow | 1 ft |
| 8-inch radius smooth 90-degree elbow | 1 ft 7 in |
| 10-inch radius smooth 45-degree elbow | 9 in |
| 10-inch radius smooth 90-degree elbow | 1 ft 6 in |
Worked example. A laundry duct needs two 90-degree elbows and one 45-degree elbow.
- Using 4-inch radius mitered fittings: 2 x 5 ft + 2.5 ft = 12.5 ft of deductions. Allowable straight duct = 35 - 12.5 = 22.5 feet.
- Using 8-inch radius smooth fittings instead: 2 x 1 ft 7 in + 1 ft = 3 ft 2 in + 1 ft = 4 ft 2 in. Allowable straight duct = 35 - 4.17 = 30.83 feet, about 30 ft 10 in.
Buying long-radius smooth elbows bought back more than 8 feet of run. Where the equivalent length exceeds 35 feet on a design permitted by the dryer manufacturer's instructions, 614.8.5 requires the equivalent length to be marked on a permanent label or tag within 6 feet of the exhaust duct connection.
Exam Trap: Two distractors live inside the 35-foot rule. First, candidates apply the 5-foot deduction to every 90-degree elbow; the 5 feet belongs only to a 4-inch radius mitered 90, while a 6-inch radius smooth 90 is 1 ft 9 in and an 8-inch radius smooth 90 is 1 ft 7 in. Second, candidates subtract the 8-foot transition duct from the 35 feet. They do not overlap: the 35 feet is measured from the connection to the transition duct to the terminal, so the transition duct sits upstream of the measurement.
A domestic gas clothes dryer exhaust uses three 4-inch radius mitered 90-degree elbows. Applying IFGC 2018 Table 614.8.4.1, what is the maximum permitted length of straight exhaust duct?