All Products / Duct Furnaces / Indoor Separated-Combustion Gas-Fired Duct Furnace (DFS Series)

DFS Series

Indoor Separated-Combustion Gas-Fired Duct Furnace

Modine’s innovative indoor, separated-combustion gas-fired duct furnace series is expertly engineered to seamlessly integrate with standard air-handling systems for air conditioning, heating, or makeup air applications. The DFS series is specifically designed for buildings with hostile atmospheric conditions, such as high humidity or negative pressures.

With an impressive selection of 10 model sizes, we offer input ratings from 100,000 BTU/hr to 400,000 BTU/hr and airflow ratings from 556 to 14,500 CFM. This versatility ensures that our duct furnaces meet a wide array of heating needs with unmatched performance and efficiency.

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Product Details & Specifications

Key Features

ETL certification for commercial and industrial use in the US and Canada.
81% thermally efficient
20-gauge aluminized steel cabinet
115V control step-down transformer with 24V gas controls
409 Stainless steel heat exchanger and burner with stainless steel separator strip
Certified to 3.0” W.C. external static pressure
Single-stage intermittent pilot with continuous retry control system for natural or propane gas operation.
Right side access to burner and gas controls (when looking into the discharge) with slide-out burner drawer
High limit safety control
Control terminal board
Provide separate electrical, venting, and gas-control access with fully gasketed doors to seal components from the environment.
Combustion air is drawn completely from outside to ensure the unit always has a constant supply of fresh, clean air
Since combustion air is introduced from outside, off-cycle vent losses are essentially eliminated, further improving building efficiency
Horizontal or vertical two-pipe or concentric venting options
Designed, Engineered & Assembled in the USA

Options

Factory-Configured & Installed Options

Input Capacities: 100, 125, 150, 175, 200, 225, 250, 300, 350, or 400 MBH

Heat Exchanger, Burner, & Drip Pan Material: All 409 Stainless Steel

Control Stage Designation: Single Stage or 2-Stage / Modulating

Access Side: Left-Hand or Right-Hand control/piping access

Air Temperature Rise (ATR) Range:
- High Temperature Rise (20°F – 100°F)
- Low Temperature Rise (20°F – 60°F)

Gas & Ignition Configuration:
- Natural Gas with Continuous Retry Ignition Controller
- Propane Gas with Lockout Ignition Controller

Gas Valve Options:
- Single Stage
- Two Stage
- Electronic Modulation
- Electronic Modulation Primary (for multiple-furnace setups)
- Electronic Modulation Secondary (for multiple-furnace setups)
- Electronic Modulation with 0–10 VDC external input signal

Safety Switches:
- Standard or Premium Control Box (no additional gas pressure switches)
- High & Low Gas Pressure Switch (Premium Control Box option)

Supply Voltage: 115V/1Ph, 208V/1Ph, 230V/1Ph, 208V/3Ph, 230V/3Ph, 460V/3Ph, or 575V/3Ph (60Hz)

Control Power Transformer: None, 40 VA, 75 VA, or 150 VA

Factory-Installed Control Devices:
- Airflow Proving Switch (Differential pressure switch)
- Timed Freeze Protection (Includes low discharge thermostat and freeze protection timer)
- Supply Air Fire Stat (Shuts system down if local temperature exceeds 200°F)
- Control Relay (Double-Pole, Double-Throw)
- Time Delay Relay (Delays blower start for heat exchanger warm-up)
- Factory-Installed Duct Thermostat (Honeywell T678A1015 shipped with ductwork sensing tube)

Accessories

Field-Installed Accessories

Separated-Combustion Vent Termination Kits (Required for DFS units):
- Separate Vent Terminals for Two-Pipe Venting
- Horizontal Concentric Vent Kit
- Vertical Concentric Vent Kit
Thermostats, Sensors, & Adjusters:
- Single-Stage Heat Only Room Thermostat (without switching)
- Single-Stage Heat and Cool Room Thermostat (with switching)
- Two-Stage Digital Non-Programmable Heating Room Thermostat (with switching)
- Two-Stage 7-Day Programmable Room Thermostat (White Rodgers)
- Duct Thermostat: Johnson Controls Electronic Temperature Control (with field-installed temperature sensor and dual relay module)
- Duct Thermostat: Honeywell T678A1015 (Field-installed version with sensing tube)
- Maxitrol Electronic Modulating Discharge Air Sensor & Mixing Tube (55°–90°F or 80°–130°F range)
- Maxitrol Set Point Adjusters (TD121 or TD121A)
- Maxitrol Room Override Thermostat (T115, 40°–90°F range)
Transformers:
- Field-Installed Step-Down Transformer (250 VA, 460V-to-115V or 575V-to-115V transformer for power exhauster motor control)
System Controls & Components:
- 7-Day Electronic Programmable Time Clock
- Mild Temperature Thermostat (Dual relay with inlet air temperature sensor)
- Photoelectronic Duct Smoke Detector (For 0.5–2.5 ft or 2.5–5.0 ft duct widths)
- Natural Gas Pressure Regulator
- Summer/Winter Switch (Double-pole, double-throw switch to disable heating in summer)
Mounting & Condensate Hardware:
- Pipe Hanger Kit (4 adapters per kit to adapt hanger points to pipe suspension)
- Drain Connector Kit (Connects drain line to the condensate drain pan)

(Note: Field Natural-to-Propane gas conversion kits are not available for separated-combustion DFS units).

Warranty

75-935 Heating and Indoor Air Quality Product Warranty

Applications

Specifically designed for commercial and industrial buildings with harsh atmospheric conditions, such as high humidity or negative pressure, the DFS series is compatible with standard air handling systems for air conditioning, heating, or makeup air applications. Common applications include:

Commercial Office Buildings
Institutional Facilities
Mechanical rooms
Gymnasiums
Multi-Purpose Rooms
Cafeterias / Kitchen Hoods
Lab Exhaust Hoods
Bathroom / Locker Rooms
Paint / Coatings Facilities
Welding Booths
Warehouse Pressurization

Tech Documents

Outdoor Power-Vented Gas-Fired Duct Furnace

Indoor Power-Vented Gas-Fired Duct Furnace

Indoor Gravity-Vented Gas-Fired Duct Furnace