Direct-Fired Indoor/Outdoor Make-up Air (MDB/MRB) - Modine HVAC

Direct-Fired Indoor/Outdoor Make-up Air (MDB/MRB)

Direct-Fired Indoor/Outdoor Make-up Air (MDB/MRB)

Designed to provide an economical and efficient means of supplying tempered make-up air. All units allow indoor or outdoor mounting and have a 100% thermal efficiency.  100% Make-up Air System is heated directly by the gas flame, eliminating the need for a heat exchanger and associated efficiency losses of indirect-fired equipment.

Return Air Direct-Fired Systems can be used as combination make-up air and heating/ventilating units, requiring the capability of operating with recirculated air as well as make-up air.

  • 100% thermal efficiency (92% sensible) results in lower fuel bills
  • Natural or propane gas manifolds are factory-assembled to provide flexible fuel options and reduce field-installation costs
  • Factory-wired electrical panel with numbered terminals significantly simplifies field wiring
  • 100% factory flame-tested
  • Weatherproof roof with drip ledge protects from water being drawn into the unit from the roof
  • 18-gauge galvanized steel casing provides high corrosion protection for long life
  • Adjustable drives through 10 HP simplify air balancing
  • Four access doors provide maximum access for easy adjustments and service
  • 22:1 firing rate turndown for optimum temperature control
  • Units are third party certified by ETL


Model MDB

  • Input ratings up to 7,425,000 Btu/hr
  • Maximum airflow capability of 60,000 CFM

Model MRB

  • Input ratings up to 5,500,000 Btu/hr
  • Maximum airflow capability of 41,000 CFM
  • Maximum return air capability of 75%
  • A minimum 25% outside air must always be supplied to the building

Both MDB & MRB

  • Painted unit casing
  • Inlet hood, unpainted* with or without filters – field installed for model sizes 125 and above
  • Insulated V-bank 2” filters section, unpainted* with permanent, throwaway, or Farr30/30 filters – field installed for model sized 125 and above and vertical units
  • Inlet damper, unpainted* – field installed for models sizes 125 and above and vertical units
  • Pillow block bearings – model sizes 110 and 118
  • Internal spring blower and motor vibration isolation – requires pillow block bearings
  • Extended grease lines – requires pillow block bearings
  • Dead front non-fused disconnect switch
  • High and low gas pressure switches
  • Building management system control options
  • Control power transformer for 208, 230, 460, or 575V supply voltage
  • Timed freeze protection
  • Mild temperature inlet on/off duct stat
  • Motor starter auxiliary contacts for starting exhaust fan
  • Double pole double throw (DPDT) control relays
  • Circuit analyzer for 10 to 12 points


  • NEMA 1 remote control panel
  • Discharge damper, unpainted*
  • Discharge louvers – 3- or 4-way, unpainted*
  • Evaporative cooler with pre-filter with 12” Celdek or Glasdek media – optional rain hood with filter
  • Evaporative cooler fill and drain kits, manual or automatic with optional freeze stat
  • Inlet stand, painted in 24” or 48” heights, with or without inlet screen – vertical units only
  • Vibration hanger – suspended units only
  • Vibration feet – slab mounted units only
  • Box style disconnect switch

*Painted options available

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