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SpacePak, Hydronics, &
Air-to-Water Heat Pumps

In addition to being the innovator of small duct high velocity systems, SpacePak is also the industry leader in air-to-water heat pump technology since we first introduced the modern hydronic solution to the North American market back in 2011.

Thanks to our parent company Mestek and its 75 year-long history as a leader in hydronic heating and cooling, SpacePak has found itself uniquely qualified to provide the levels of training and support required for us to be the driving force behind the adoption of this exciting and promising technology.

With thousands of rock-solid installations across the US and Canada, we've taken our original Solstice heat pump technology that's proven itself in the field over the last decade, and upgraded our product offering with the inclusion of the latest innovations in inverter technology.

Achieve carbon free comfort with air-to-water heat pumps

Hydronic Heating & Cooling
with Air-to-Water Heat Pumps

  • Environmentally friendly heating and cooling for residential and light commercial settings
  • The physics that make water ideal for conveying heat also make it ideal for cooling
  • All the advantages of a hydronic (water) distribution system without the use of fossil fuels
  • Combines the performance of modern air-source heat pump technology with the unsurpassed comfort of hydronics
  • 30% more efficient than traditional air-source heat pumps
  • Energy savings up to 47% greater than a typical high efficiency natural gas condensing boiler
  • Up to 70% less electricity use than electric baseboard

Basic Hydronic System Layout

Air-to-water heat pump basic hydronic system layout

The graphic reflects the design flexibility afforded with air-to-water heat pumps and the diverse array of hydronic emitters available to choose from for operation in a modern hydronic low temperature system.

SpacePak Hydronic Fan Coil Options

  • Low Temperature HighWall
  • Low Temperature ThinWall
  • Small Duct High Velocity Hydronic Air Handler

Third Party Emitter Options

  • Radiant Panels (Floors, Ceilings, Walls)
  • Low Temperature Hydronic Baseboard
  • Panel Radiators (not represented in graphic)
Chart of recommended supply water temperatures for modern hydronic systems

Solstice Heat Pumps
Industry Leading Air-to-Water Technology

Industry Proven Technology for Reliability, Performance, & Longevity

  • High COP hydronic heat pumps that supply low temperature water for heating & chilled water for cooling
  • Thousands of installations across the US and Cananda
  • Industry proven Solstice technology
  • Eligible for rebates!
  • Extended warranty for SpacePak Certified Contractors:
    • Industry leading 10-year compressor warranty
    • 5-year parts warranty
Solstice Inverter Monobloc Air-to-Water Heat Pumps
Solstice Inverter Extreme Air-to-Water Heat Pump
Solstice Inverter Split Air-to-Water Heat Pump
Solstice heat pumps logo

Solstice Inverter Monobloc
Air-to-Water Heat Pump

The Solstice Inverter Monobloc (SIM) air-to-water heat pump uses inverter compressors and DC driven fan motors for optimal load matching and has an advanced touch screen control for easy user interface.

Keeps all refrigerant conveniently located outside the home and is capable of low ambient cooling.

Available in 3 and 5 ton models.

Solstice Inverter Monobloc (SIM) Air-to-Water Heat Pump units

Standard Features & Benefits

  • Industry Proven Solstice Technology
  • Reliable Mitsubishi Inverter Compressor
  • Monobloc Design (No On-Site Refrigerant Charging)
  • Keeps All Refrigerant Outside the Occupied Space
  • Low Ambient Cooling
  • Domestic Hot Water Offset
  • Freeze Protection
  • Low Amp Draw with Ultra Quiet Operation
  • User Friendly Touch Screen Control
  • Precision Temperature Control Platform
  • DC Driven Fan Motors
  • No Refrigeration License Required During Installation (in most states)

SIM-036 (3 ton)

Heating Capacity Range: 13,200 - 38,700 Btu/h*
Cooling Capacity Range: 1 – 3 tons*
COPs: up to 5.01*
EER: up to 12.97*


SIM-060 (5 ton)

Heating Capacity Range: 25,400 – 70,600 Btu/h*
Cooling Capacity Range: 1.5 – 5 tons*
COPs: up to 4.67*
EER: up to 11.60*

*Using AHRI 550/590 Test Criteria
Solstice heat pumps full inverter series logo
Solstice Inverter Monobloc Video

Solstice Inverter Split
Air-to-Water Heat Pump

The Solstice Inverter Split (SIS) air-to-water heat pump is capable of high performance in heating mode at low ambient temperatures.

Its’ split-type construction provides installers with the flexibility to reduce the use of glycol in the hydronic loop and the convenience of simple piping similar to typical residential wall-hung boilers.

Available in 5 ton model.

Solstice Inverter Split (SIS) Air-to-Water Heat Pump indoor and outdoor units

Standard Features & Benefits

  • Industry Proven Solstice Technology
  • Reliable Panasonic EVI Inverter Compressor
  • Extreme Low Ambient Heating Performance to -20°F
  • Split Design Provides the Flexibility to Reduce the Use of Glycol in the Hydronic Loop
  • Simple Indoor Piping Similar to Wall Hung Boilers
  • SIS System Includes both Indoor and Outdoor Units, Refrigerant Line Set (35'), and Control Wire (50')
  • Freeze Protection
  • Low Amp Draw with Ultra Quiet Operation
  • User Friendly Touch Screen Control
  • Precision Temperature Control Platform
  • DC Driven Fan Motors & EC Modulating Fans

SIS-060A4 (5 ton)

Heating Capacity Range: 20,500 - 71,500 Btu/h*
Cooling Capacity Range: 2.5 - 5.2 tons*
COPs: up to 3.09*
EER: up to 12.5*


*Using AHRI 550/590 Test Criteria
Solstice heat pumps full inverter series logo
SpacePak HighWall low temperature hydronic fan coil
SpacePak ThinWall low temperature hydronic fan coil
SpacePak WCSP hydronic air handler
SpacePak Buffer Tanks
SpacePak Hydronics logo

Better than Geothermal


  • Up to 30%-50% lower installation cost when compared against Geothermal systems.
  • Little-to-no outdoor excavation needed.
  • Low Amp Requirements
  • Keeps refrigerant outside the home and utilizes a condenser coil that is 30% larger than standard units, improving efficiency.
  • Allows custom control not obtainable by most traditional refrigerant-based systems.
  • Utilizes adjustable water flow, water temperature, and airflow settings, giving you complete control of the system and each temperature zone.
  • Features an intelligent factory-configured control platform, with a self-diagnostic microprocessor that keeps your system running seamlessly.


  • Water-to-water heat pumps, or geothermal heat-pumps, work by installing multiple “earth loops,” or water lines, throughout your front yard.
  • Expensive to install, especially if vertical bore holes are required for the earth loop, or if you’re connecting multiple earth loops to the heat pump.
  • Most water-to-water heat pumps can only heat your home, but have limited cooling capabilities.
  • Horizontal earth loops require large land areas and major excavation, and most jobs require re-landscaping your yard.
  • Depending on your region, drilling may be necessary for installation.
  • While most geothermal heat pumps claim to be highly efficient, this usually doesn’t include the power required to move flow through the earth loop, which can be substantial.

Case Studies

A Compact Design

The historic First Presbyterian Church of Lancaster, PA needed to replace two 50 ton chillers. Limited area surrounding the building presented extreme challenges in getting a large unit to the roof. Instead of renting a crane and shutting a street down, the Solstice’s compact design made it possible to take the 21 Solstice SE Heat Pumps up the church's elevator to the roof and provide the 105 tons of heating and cooling demanded.

-J & G Heating and Air Conditioning
Historic Presbyterian Church with five Solstice SE air-to-water heat pumps on the roof
Habitat for Humanity house in cold-climate Vermont with Solstice Extreme low ambient air-to-water heat pump installed

Creating an Affordable, Energy Efficient Home with Habitat for Humanity

This year, SpacePak teamed up with the Rutland, Vermont chapter of Habitat for Humanity in support of their most recent project to build a new and highly energy efficient home for a family in need of affordable housing. Efficiency Vermont, the state’s objective advisor on saving energy through efficiency, identified SpacePak’s cold-climate-tested air-to-water heat pump as the ideal solution to deliver affordable heat energy to the home’s hydronic heating system. The house was also equipped with radiant tubing in a concrete slab on the first floor, and baseboard tubing on the second floor. The system consists of two zones, each controlled by a separate thermostat on each floor, allowing the family to program the home’s temperature settings and further reduce their utility bills.

Learn more about SpacePak!


Contact Your Local Representative