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Air to Water Heat Pump (ATW), Monoblock or Split? Each Configuration has its Pros and Cons... 

Whether Monoblock or Split Configuration, ATW Heat Pumps remain a smart investment for customers not willing to break the bank to have a complete Renewable Energy Heating/Cooling System. A right answer for one project could be the wrong one for another. This Blog will outline the characteristics of each configuration (Split or Monoblock) and will leave the choice for the Designer, Installer or Client.

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Electricity Prices rose up significantly this year in many Canadian Provinces. This rising utility rates trend will continue in the future, since local governments are gradually pushing Canadians to use less and less Energy by tightening energy efficiency requirements in every new version of building code. This is a major challenge for both home owners (or to be home owners), designers, contractors and equipment suppliers since they must come up with new products in order to meet up with the higher sustainability standard. 

natural light

With many Canadians spending more time at home due to long winter, COVID-19 Pandemic and aging population, demand for natural light in indoor spaces is on the rise. More natural light means larger Fenestrated Building Envelopes which require more and more energy to provide an acceptable indoor living standard.

With Rising Energy Prices, tougher Environmental Regulations combined with demographic and living standard changes, Air to Water Heat Pumps are the most affordable answer to the previously listed requirements. Air to Water Heat Pumps are HVAC devices (called Mini Air Cooled Chillers in Europe) producing Chilled/Hot Water (or Water/Glycol Mixture) that can be used for Space Heating and Cooling as well as Domestic Hot Water (DHW) Heating. ATW Heat Pumps are equipped with a DC Inverter Compressor and the Split Configuration has the EVI (Enhanced Vapor Injection) technology, which make them able to operates at a temperature range from -25°C to 45°C



Monoblock Air to Water Heat Pump

Monoblock ATW Heat Pumps is comprised of one piece destined to be installed outdoor. When used in outdoor climates with peak winter temperatures below 0°C (32°F), a Propylene Glycol/Water Mixture shall be used as a heat transfer fluid to avoid freezing. Mixture Glycol Concentration % depends on lowest winter temperature. In most major Canadian Cities a 50% Water / Propylene Glycol Mixture is used.

Monoblock ATW Heat Pump requires external pump for pumping heat transfer fluid (whether Water or Water/Glycol Mixture). In Winter time, Monoblock ATW Heat pump goes into cooling mode (in other terms it draws heat from the indoor space) to defrost the ice accumulated on its evaporator. Monoblock Heat Pump requires an external heat source for its defrost operation in winter.

Split Air to Water Heat Pump

Split ATW Heat Pump is comprised of two pieces. One piece called the outdoor unit is destined to be installed outside and the second piece, called the indoor unit is destined to be installed inside. Split ATW Heat Pump does not require Water/Glycol Mixture in cold climates, since the link between indoor and outdoor unit is made by refrigerant copper lines (refrigerant is a fluid that does not freeze).

Split ATW Heat Pump are equipped with integrated variable speed circulation pump as well as a heater for defrosting the heat pump outdoor unit in winter time. Variable Speed Pump helps increasing the energy efficiency of the heat pump and the integrated heater (3 or 5 KW) prevent the external backup heater (11-20KW) from running at full capacity when defrost demand is present. 

ATW Configurations Cost Analysis

Air to Water Heat Pump can be installed to provide either Chilled Water or Hot Water and Pre-Heat DHW or Chilled Water and Hot Water and DHW Pre-heating. In both cases price difference is driven by machine, glycol, pump and manpower individual prices.

Heating or Cooling with DHW Pre-Heating

Cooling or Heating

Simultaneous Heating and Cooling with DHW Pre-Heating

simultaneous cooling and heating

The above schematics depict the 2 most common installations of Air to Water Heat Pumps. The one on the left is for places where simultaneous Cooling / Heating is rare, so one tank with indirect coil is used to preheat DHW to temperatures as high as 130°F (or 55°C) and the other tank is used for either space heating or space cooling. In the schematic on the right, One indirect tank is used for DHW pre-heating and space heating and the other tank is dedicated for chilled water. 

When Heat Pump are used to serve largely Fenestrated Properties with a South and North Exposures, area beside the southern façade could have a cooling demand (even in mid-winter temperatures) and area beside the northern façade will have a heating demand.

ItemMonoblock HSS030V2 SPLIT HSS030V2LS
Heat Pump Selling Price4,7005,792
50% Glycol - 16 Pails - Selling Price (required to fill 2 x 40 US Gallons Tanks)2,176
External Heater for Defrost  (a Thermolec Mini-Boiler)902
Manhours Cost for the Installation of Refrigerant Copper Lines Between Indoor and Outdoor Unit480
Circulation Pump Selling Price280
Total Cost (CAD $)8,0586,272


Even though Monoblock Heat Pumps are cheaper than the split ones, Complete Installation of Split ATW heat pump is always cheaper to customer. Assuming that water is free to be used as a heat transfer fluid in Split Heat Pumps installations, the cost of buying a good quality glycol with proper inhibitor concentration as well as the cost of circulation pump make the Monoblock heat pump installation more expensive.

Monoblock Heat Pumps are more popular among DIY customers because they think it's cheaper (before calculating the overall cost of the project) and it's like plug and play device. Split ATW Heat Pump requires a professional for the installation and commissioning of the refrigerant copper lines which makes it not appealing to some DIY Customers.


  • wellpoint dewateringDec 10, 2020

    Wonderful information, thanks a lot for sharing kind of content with us. Your blog gives the best and the most interesting information on air to water heat pump monoblock or split find out pros and cons of each configuration. I wonder if we can gather such practical information about it, a great post definitely to come across.

  • ROGEROct 13, 2020

    Thank you a lot for your comment. You do require a hot water tank (mandatory) and a chilled water tank (not mandatory when the capacity of your hydronic Air Handling unit is similar to the heat pump one).

    The space required for this type of installation depends on the size of your storage tank, that depends whether you have an off peak/on peak utility rates or not. But a 50ft2 space is more than enough for this type of installation.

  • Mark PurchaseOct 13, 2020

    Just curious about this system as a replacement to my existing set up. I have a ~25-30 year old boiler for my DHW (not hot water tank) and baseboard heating. From the diagram this appears to require 3 water tanks inside. Would I need to replace my existing oil boiler? What kind of space is required to install this system?


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