The Steffes Serenity furnace (4200 series) combines forced air heating with Electric Thermal Storage (ETS) technology to deliver reliable, consistent heat to every corner of your house. It is explicitly designed to replace your existing oil-burning or gas/electric furnace system. The Serenity’s exceptionally efficient operation utilizes low-cost, off-peak electricity to provide economical and comfortable heating.

Heating your home with Steffes’ Serenity Forced Air Furnace gives you:

  • Confidence that you are providing a consistently comfortable environment for your family.
  • Reassurance that you are contributing to a lower-carbon future for your children and community.
  • Comfort that you have chosen the most efficient and environmentally-friendly system for your home.

Steffes Electric Thermal Storage (ETS) systems work smarter, cleaner and greener to deliver increased warmth and reduced energy costs. Forced air, hydronic or room units – Steffes offers premiere heating solutions for any home configuration.

Explore Steffes ETS in our virtual home experience. This interactive walk-through illustrates how each Steffes system works with your home to increase comfort and efficiency.


With Heat Pump

Serenity System Installed with a Heat Pump

Heat pump systems are one of the most efficient methods of heating and cooling. Utilizing a Serenity Forced Air Furnace with a heat pump allows the heat pump’s high efficiency to be combined with off-peak electric rates making this heating and cooling system the lowest operation cost option. In addition, the Serenity ensures comfort regardless of outdoor temperature.

In heat pump applications, the Serenity replaces the resistance strip heat or secondary heat, which is typically required as a supplement or backup to heat pump systems, with low cost, off-peak stored heat. As outside temperatures decline the stored heat in the Serenity is used in conjunction with the heat pump’s heating capacity to satisfy comfort requirements. During on-peak hours or when the demand for heat is at the point where the heat pump alone cannot satisfy the heating requirements, the stored heat is used to supplement the heat pump. The Serenity allows the heat pumps efficiency to be utilized even during cooler outdoor temperatures.

The Serenity/Heat Pump system offers significant benefits:
  • Provides great comfort 24 hours a day
  • Provides for a high efficiency, low cost heating and cooling system all in one
  • Optimizes system performance by allowing the heat pump’s efficiency to be fully utilized
  • Eliminates the cool discharge air temperatures associated with heat pump systems during low outdoor temperatures
  • The Serenity/Heat Pump combination, when used with off-peak electric rates, is the most economical heating and cooling system available.
How the System Works
  1. The room thermostat in the home is set to desired comfort level. If room temperature decreases below the room thermostat set point, the system is energized to deliver heat.
  2. Upon a heat call from the room thermostat, the heat pump’s outdoor compressor unit is energized and warms the A-coil in the return air duct of the Serenity. At the same time, the Serenity’s supply air blower is energized.
  3. The supply air blower draws air from the home (shown at 68° F) across the air filter and the heat pumps A-coil extracting heat from the coil as it passes through it.
  4. A sensor monitors air temperature after the A-coil. If the air temperature is warm enough to provide comfort to the homeowner (generally 90° F or higher), the supply air blower simply delivers the warm heat into the home through the supply air duct. Air temperature after coil in the diagram is shown at 85° F.
  5. If air temperature after the heat pump coil is below a comfortable level (generally less than 90° F), the Serenity’s core blower will modulate low cost, “Off-Peak” stored heat into the duct stream so comfortable heat (generally 90° F or higher) can be delivered into the home.
  6. Since heat pumps generally have an operating efficiency of 150%-300% or greater (depending on outdoor temperature), the Serenity system first utilizes the heating ability the heat pump offers. If the heat pump doesn’t have the ability to satisfy comfort and space heating requirements, the Serenity system starts to work with the heat pump utilizing low cost, off-peak energy to ensure comfort for the user at all times. Combining the heat pump’s efficiency with the “Off-Peak” Serenity system yields very low operating costs for the end user along with great comfort.


100 percent efficient

No maintenance required

Built-in digital thermostat

Variable speed supply blower

Immediate heat response

Super insulated to minimize static discharge and surface temperature

Easy to read digital display

Five-year limited parts warranty


4200 series Serenity Forced Air Furnace

MODEL 4210
Charging Input (kW) 16.0 kW
Single Feed: Minimum Circuit
     Ampacity (includes 25% derate for continuous load)
91.5 AMP
Charging Circuits Required 2 – 60 AMP,
1 – 15 AMP
Maximum Core and Supply Blower Load 7 AMPS
Element Voltage 240 V
Blowers/System Controls Voltage 240 V
Storage Capacity
80 kWh
284,300 (BTU)
Dimensions Including Air Handler
(W x D x H in inches)
43” x 44” x 47”
Duct openings (inches)
     Supply Air Outlet
     Return Air Inlet*
18.6” x 18.1”
16” x 16”
Appropriate Cabinet Weight 325 lbs
Approximate Brick Weight 1,116 lbs
Approximate Air Handler 95 lbs
Approximate Installed Weight 1,536 lbs
Number of Elements  8
Number of Bricks 72
**Paired Indoor Coil Capacity
     Front access dimensions
     Inner dimensions (W x D x H in inches)
1 ½ to 3 TON
20” x 20”
21″ x 21” x 22.5″

*The return and supply air plenums can be ordered as optional pieces with the 4200 series systems. They must be installed on the correct opening . Any ducting must accommodate the opening sizes at a minimum.

**Serenity can accommodate most heat pump or air conditioner indoor coils, provided the heat pump or air conditioner is sized in accordance to supply air delivery fates of the system. A return air plenum can be ordered as an optional accessory with Serenity. The dimensions listed are those that the optional return air plenum can accommodate. For larger coils, the return air plenum must be installer supplied. If using an air conditioner or heat pump system, that system must include the indoor coil or the outdoor compressor system as standard equipment.

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