Airxcel Suburban SF Series

This document describes the Suburban Gas Furnaces, specifically models SF-20Q, SF-25Q, SF-30Q, SF-35Q, SF-42Q, SF-20FQ, SF-25FQ, SF-30FQ, SF-35FQ, and SF-42FQ, designed for installation in recreational vehicles (RVs).

Function Description:

These furnaces provide heating for RVs by burning propane gas. They are designed to draw combustion air from the outside atmosphere and vent exhaust gases to the outside, preventing infiltration of combustion products into the living space. The units are controlled by a thermostat, which initiates blower operation and then the main burner ignition. A safety shut-off switch is integrated to prevent operation if the vent is covered. The furnace is designed for easy removal from the exterior of the RV for maintenance or replacement.

Important Technical Specifications:

Models: SF-20Q, SF-25Q, SF-30Q, SF-35Q, SF-42Q, SF-20FQ, SF-25FQ, SF-30FQ, SF-35FQ, SF-42FQ.
Fuel Type: Propane gas only. Conversion to natural gas is not supported.
Gas Supply Pressure: Minimum 11" W.C. (Water Column), Maximum 13" W.C. (Water Column).
Electrical System: Negative ground 12-volt D.C. system only. Not compatible with positive ground or 115-volt A.C.
Circuit Protection: Must be connected to a protected circuit fused for not more than 20 amps.
Wiring: All wires are 18 AWG unless otherwise specified. If original wires are replaced, they must be rated for at least 105°C. Recommended wire gauge is No. 12 for power supply to minimize voltage drop.
Ignition: Equipped with an electric igniter device with an energy consumption of 0.1 amp @ 12 volts D.C.
Ventilation: Requires two 2-1/4" or 2-3/4" diameter holes through the outer panel for exhaust and intake tubes. Minimum overlap for intake tube is 1/2", and for exhaust tube is 1-1/4". Extension tubes are available for various wall thicknesses (0" to 9").
Return Air Requirements:
- SF-20/25/30Q, SF-20FQ/25FQ/30FQ: 55 Sq. In.
- SF-35Q/35FQ: 55 Sq. In.
- SF-42Q/42FQ: 142 Sq. In. (can be reduced to 88 Sq. In. if 5 ducts are used).
- Return air must be from the living area of the coach, not from cargo areas or "Toy Boxes."
Ducting:
- Minimum open duct areas (Side, Top, Bottom) vary by model, e.g., SF-20Q/20FQ requires 25 Sq. In. for side ducts (2 x 4" ducts), 56 Sq. In. for top, and 56 Sq. In. for bottom.
- SF-42Q Bottom Duct requires a specific kit (Part No. 520753).
- Ducts terminating in dead air spaces or smaller than 2" diameter should not be counted in the required duct area.
- No outlet register should be placed within 18" of the return air opening, or directed towards it if installed at 90 degrees.
Clearances: Minimum 1/4" clearance where ducts pass through combustible construction (UL listed duct materials can be 0" clearance). A 6" minimum clearance is required between the furnace vent and any door when open.

Usage Features:

Safety First: Users are warned not to operate the furnace while the vehicle is in motion or being towed, or if the vent is covered.
Gas Leak Detection: If gas is smelled, evacuate the vehicle, shut off gas supply, avoid electrical switches, and contact a qualified service technician or fire department. Never check for leaks with an open flame; use soapy water.
Thermostat Control: The thermostat should be located approximately 4-1/2 feet above the floor, away from heat sources. It must have no voltage output to the return leg when in the "OFF" setting or no call for heat. Adjustable anticipators should be set at 0.7 amps, with adjustments in 0.5 amp increments for desired heating cycle length.
Start-up Procedure: Turn manual gas valve to "OFF," set thermostat above room temperature to start blower (allow 5 minutes for combustion chamber purge), then set thermostat below room temperature to turn blower off (allow 2 minutes). Open manual gas valve, set thermostat to desired temperature, and allow 30 seconds for main burner ignition.
Shut-down Procedure: Set thermostat to lowest setting, then to "OFF." Turn manual gas valve to "OFF."
Lock-out Feature: If the burner does not light after three attempts, the furnace will lock out, and the blower will remain off until the unit is reset by reactivating the thermostat or cycling power.

Maintenance Features:

Annual Inspection: The furnace should be inspected yearly by a qualified service agency before the heating season. This includes checking the installation, vent termination, combustion chamber, venting for physical soundness, and proper overlap of vent tubes.
Monthly Inspection (User): Owners should inspect the furnace monthly for soot on the vent. Soot indicates incomplete combustion and an unsafe condition; immediate shutdown and contact with a qualified service agency are required if soot is observed.
Cleaning: Keep the furnace clean, especially control compartments, burners, and circulating air passageways. The motor is permanently lubricated and requires no oiling.
Combustion Chamber Cleaning: To clean the combustion chamber, the furnace must be removed from the cabinet and manifold. The blower assembly and controls are removed, leaving only the chamber and firewall. Compressed air is then used to blow out soot or loose debris.
Gasket Inspection: All gaskets should be inspected for signs of leakage or deterioration and replaced if necessary to ensure tight seals for safe operation.
No Screens on Vent: Do not install screens over the vent, as they can become restricted and cause unsafe operation.
No Unauthorized Parts: Only factory-authorized parts should be used for repairs.
No Alterations: Do not alter or modify vent tubes or other components, as this can lead to unsafe operation.
Professional Service: Installation and service must be performed by a qualified installer, service agency, or gas supplier. Never attempt to repair damaged parts or the furnace yourself.

Warranty:

Two-Year Limited Warranty: Covers defects in material and workmanship under normal use and maintenance for two years from the date of purchase. Suburban will replace defective parts and pay a warranty service allowance to recommended service centers. Proof of purchase date is required.
Three-Year Limited Warranty on Heat Exchanger: Extends coverage for the heat exchanger for the third through fifth year after the date of original purchase, covering material and workmanship defects. Labor reimbursement is not included for this extended warranty.