Ducted (Air-Source) Heat Pump

Ducted Heat Pump Systems extracts heat from the air and transfers heat to either the inside or outside of your home depending on the season.

Winter – Heat pumps move heat from the cool outdoors into your warm house.

Summer – Heat pumps move heat from your cool house into the warm outdoors.

Ductless Heat Pumps (Mini Splits)

Ductless Heat Pumps are perfect solutions for clients who:

  • Currently heat with electric baseboard.
  • Wish to supplement existing boiler system.
  • Don’t have a central air handling system.
Heat pump internal image

Air-source heat pumps can be add-on, all-electric or bivalent:

Add-on heat pump – Designed to be used with another source of supplementary heat, such as an oil, gas or electric furnace.

All-electric air-source heat pump – Comes equipped with their own supplementary heating system in the form of electric-resistance heaters.

Bivalent heat pump – A Special type of heat pump, developed in Canada. It uses a gas or propane fired burner to increase the temperature of the air entering the outdoor coil. This allows these units to operate at lower outdoor temperatures.

How a Heat Pump Works:

An air-source heat pump has three cycles: the heating cycle, the cooling cycle and the defrost cycle.


During the heating cycle, heat is taken from outdoor air and “pumped” indoors.

  • First, the liquid refrigerant passes through the expansion device, changing to a low-pressure liquid/vapour mixture. It then goes to the outdoor coil, which acts as the evaporator coil. The liquid refrigerant absorbs heat from the outdoor air and boils, becoming a low-temperature vapour.
  • This vapour passes through the reversing valve to the accumulator, which collects any remaining liquid before the vapour enters the compressor. The vapour is then compressed, reducing its volume, causing it to heat up.
  • Finally, the reversing valve sends the gas, which is now hot, to the indoor coil, which is the condenser. The heat from the hot gas is transferred to the indoor air, causing the refrigerant to condense into a liquid. This liquid returns to the expansion device and the cycle is repeated. The indoor coil is located in the ductwork, close to the furnace.

The ability of the heat pump to transfer heat from the outside air to the house depends on the outdoor temperature. As this temperature drops, the ability of the heat pump to absorb heat also drops.

At the outdoor ambient balance point temperature, the heat pump’s heating capacity is equal to the heat loss of the house.

Below this outdoor ambient temperature, the heat pump can supply only part of the heat required.

In heating mode without any supplementary heat, the air leaving a heat pump is cooler than air heated by a normal furnace. Furnaces generally deliver air to the living space at between 55°C and 60°C. Heat pumps provide air in larger quantities at about 25°C to 45°C and tend to operate for longer periods.


The unit takes heat out of the indoor air and rejects it outside.

  • As in the heating cycle, the liquid refrigerant passes through the expansion device, changing to a low-pressure liquid/vapour mixture. It then goes to the indoor coil, which acts as the evaporator. The liquid refrigerant absorbs heat from the indoor air and boils, which becomes a low-temperature vapour.
  • This vapour passes through the reversing valve to the accumulator, which collects any remaining liquid, and then to the compressor. The Vapour is compressed as its volume is reduced, causing it to heat up.
  • Finally, the gas, which is now hot, passes through the reversing valve to the outdoor coil, which acts as the condenser. Heat from the hot gas is transferred to the outdoor air, causing the refrigerant to condense into a liquid. This liquid returns to the expansion device, and the cycle is repeated.

During the cooling cycle, the heat pump also dehumidifies the indoor air. Moisture in air passing over the indoor coil condenses on the coil’s surface. Then collected in a pan at the bottom of the coil. A condensate drain connects this pan to the house drain.


In heating mode, when outdoor temperature falls below freezing, moisture in the air will condense and freeze on the coil. The amount of frost buildup depends on the outdoor temperature and the amount of moisture in the air.

This frost buildup decreases the efficiency of the coil by reducing its ability to transfer heat to the refrigerant. To remove frost the heat pump will switch into the defrost mode.

  • First, the reversing valve switches the device to the cooling mode. This sends hot gas to the outdoor coil to melt the frost.
  • While this is happening, the heat pump is cooling the air in the ductwork.

There are 2 methods of defrost mode. Demand-frost controls monitor airflow, refrigerant pressure, air or coil temperature and pressure differential across the outdoor coil to detect frost accumulation on the outdoor coil.

Time-temperature defrost is started and ended by a preset interval timer or a temperature sensor located on the outside coil. The cycle can be initiated every 30, 60 or 90 minutes, depending on the climate and the design of the system.

Unnecessary defrost cycles reduce the seasonal performance of the heat pump. The Demand-frost method is generally more efficient since it starts the defrost cycle only when it is required.

Heat Pump Advantages:

Move Heat Rather Than Generate Heat – Heat pumps can provide up to 4 times the amount of energy they consume. This is possible because a heat pump moves heat from the air rather than converting it from a fuel.

Savings –  You may be able to reduce your heating costs by up to 50 % if you convert from an electric furnace to an all-electric air-source heat pump.

Dehumidify – High-efficiency heat pumps also dehumidify better than standard central air conditioners, resulting in less energy usage and more cooling comfort in summer months.

Comfort – Heat pump systems deliver constant, even temperatures, and are quiet inside and out.

Durability –  With routine maintenance, heat pump systems are typically durable and highly reliable. A properly maintained and installed heat pump can deliver service for 20 years or more.

Heat Pump Energy efficiency ratings: SEER and HSPF

Heat pumps have 2 efficiency ratings because they both cool and heat the home:

  •  SEER (Season Energy Efficient Ration) – is the cooling efficiency, and ranges from 13 to the 20s (it’s rising as technology advances).
  • HSPF (Heating System Performance Factor) – is the heating efficiency and ranges from 7.7-10.

For Canadians a higher HSPF rating will have a larger impact on yearly energy bills and cost of operation than what SEER ratings will.


Proper maintenance is critical to ensure that your heat pump operates efficiently and has a long service life. You can do some of the simple maintenance yourself, but you may also want to have a a professional service contractor do an annual inspection of your unit. The best time to service your unit is at the end of the cooling season, before the start of the next heating season.


Filter and coil maintenance has a dramatic impact on system performance and service life. Dirty filters, coils and fans reduce airflow through the system. This reduces system performance, and can lead to compressor damage if it continues for extended periods of time.

Inspect filters monthly, and clean or replace as required by the manufacturer’s instructions. Vacuum or brush clean the coil at regular intervals as indicated in the manufacturer’s instruction booklet. Hose down the outdoor unit with a garden hose. While cleaning filters and coils, look for symptoms of other potential problems.


Clean the fan. Lubricate fan motor only if the manufacturer instructions specify. Maintain annually to ensure that the fan provides the airflow required for proper operation.

Check the fan speed at the same time. Incorrect pulley settings, loose fan belts, or incorrect motor speeds in the case of direct drive fans can all contribute to poor performance.


Inspect and clean ductwork as required. Check for loose insulation, abnormal buildup of dust, or any other obstacles that occasionally find their way through the grilles.

Do not restrict airflow. Ensure vents and registers are clear of furniture, carpets or other items. Extended periods of inadequate airflow can lead to compressor damage.

You will need to hire a competent service contractor to do more difficult maintenance such as checking the refrigerant level and making electrical or mechanical adjustments.

Contact E.T. Mechanical Ltd. today! We can assess your heating and comfort needs, maintain your heating and cooling systems, and help you save on your energy bill.

Heat Pumps – Frequently Asked Questions

What temperature is a heat pump not effective?
Every heat pump is different, it is best to check the temperature rating of your specific heat pump model.  In colder climates (Canada), cold climate heat pumps are installed that are rated for colder temperatures. Depending on the specific heat pump this can be from -15 °C, or even as low as -30°C.
Do you really save money with a heat pump?
Heat pumps are one of the most energy efficient ways to heat your home.  Instead of using energy to generate heat, it extracts heat from the outside air and transfers it into your home by means of refrigerant that is circulated by a compressor. A ductless heat pump can save you 30 – 40% or more on your utility bill.

With the added benefit of being able to cool your home in the summer months. Heat Pumps not only helps you save, but contribute to year round comfort.

How does my heat pump work with my other heat source?
Your heat pump is designed to run efficiently until -10°C,-15°C, or -25°C (without wind chill) depending on which model is installed in the home. All heat pumps require an alternative source of heat. The system can work efficiently until these temperatures are reached. At that time, some systems should be shut off, while others will automatically do so. Running electric baseboards or other sources of heat is necessary approaching these temperatures.

During cold winter months (February & January) a power bill should be expected to rise as the system has less ideal temperature to run. The entire season’s results will show savings. Relative to outdoor temperature and where the heat from a system will travel, it may also be necessary to run heat sources (ex. Electric baseboard) in other parts of the home. Don’t worry, as these sources will only be supplementing at a fraction of their regular use. To some measure, heat from the ductless system will reach these areas, and less heat is produced by the alternative (such as electric baseboard) in order to reach a comfortable temperature.

We recommend all systems be shut off at -15°C (with the exception of our cold climate heat pumps), this will assist the lifespan of the unit as it works hardest during colder temperatures. This will also maintain efficiency of the unit, as at this temperature the cost of operation is the same as electric baseboards.

Why is my heat pump making a temporary rushing water/ crackling sound/ vibrating noise?
All heat pumps will have a defrost cycle that will take place more often as the temperature drops. After running for a period of time, the system creates frost that must be melted away from the outdoor unit. This happens by temporarily reversing the flow of refrigerant which makes a strange sound in the home. This can be as often as every 45 minutes or sooner in colder temperatures; it is necessary for your system to maintain its efficiency.
It is cold outside; why is my heat pump not working?
When the outside air temperature drops below 4 – 5 °C, your heat pump may go into defrost mode.

It may also make an unusual sound when this mode is activated. In this mode your heat pump may not appear to be pumping out hot air.  If this is the case, it is best to leave the unit alone until it has gone through this cycle.  If you know it is going to be cold and frosty overnight, you can be sure your system will go through at least one of these cycles. The colder the temperatures that a heat pump operates at, the more often defrost cycles must occur. The unit is removing frost and ice buildup, in order to run as efficiently as possible.

Should I turn my Heat Pump off at night?
It’s generally much more efficient to leave your heat pump running, opposed to turning the heat source off/down when not needed as with other traditional means of heating (wood furnace, electric baseboard, etc.).

Heat pumps are most efficient when they slowly maintain the temperature of the room. When a large difference in  temperature is required (more than 1°C), compressors ramp up, and a heat pump will activate alternate/backup modes of heating in order to quickly achieve temperature.

It is possible to turn a heat pump down overnight. Program the system to drop 1°C every hour, and rise 1°C every hour to when you wake up.

Generally it is recommended to have the home stay a consistent temperature.

How often do I need to clean my heat pump?
It is important that you check and clean the filters on your indoor unit every 2 weeks. Keeping the filters clean will help your Heat Pump run efficiently.

E.T. Mechanical recommends becoming a club member to guarantee an annual visit by our technicians. This will help your unit to continue to run as specified and to its full capabilities.
For more information on how to best keep your filters clean see our user guide.

How high can I increase the temperature on my Heat Pump?
Your heat pump will be able to gradually reach a wide range of temperatures. However in order to maintain the best possible efficiency by the product, the largest  increment in temperature should 1°C each hour. By gradually turning up the temperature, the heat pump doesn’t have to use alternate sources of heat to achieve temperature, or ramp up the compressor.
Why does my heat pump blow cold air when it starts/or runs?
This occurs because the heat pump and the indoor blower fan start at the same time and the heat pump requires a few seconds or minutes to build up the required heat with the refrigerant.
Heat Pumps are designed to gradually rise to a desired temperature over a long period of Time with a small heat output and a large amount of air flow. A comfortable temperature could be considered 22°C, yet our body temperature is 37°C; because the Heat Pump is producing air potentially colder than our body temperature the outputted air could seem lukewarm or
even slightly cold to the touch. Don’t worry; this is part of its normal operation of being efficient and producing proper comfort.
What is that smell coming from my new heat pump?
More than likely what you smell is the backup emergency heat or electric heating elements in your comfort system. The backup heat will activate when it’s very cold out, or a large temperature increase (larger than 2°F or 1°C) has been requested. It can also activate when heat is detracted from the home – opening doors or windows, outside gusts of wind, etc.

After cooling season aux heating elements that have been unused for an entire season have been coated with dust, once auxiliary heat is initiated this dust burns off and has a temporary but distinct odor.

Do I need to clear the snow from around my heat pump?
The outdoor unit of a heat pump relies on air flow to operate properly at all times. Snow must be cleared from around the unit leaving a clearance of 2 to 3 feet minimum surrounding the unit. Heat pumps must be elevated off the ground to allow the water produced during the defrost cycle to flow away from the unit. Snow build up at the bottom few inches of the unit can prevent the unit from completing the defrost cycle properly. If the snow is not cleared, the unit will not function properly. If the system is operated under these conditions it has potential to damage a unit, even for only a short period of Time.
What’s the whooshing sound coming from my ductwork?
In smaller houses where duct work that was used for an alternate form of heating is present, you may notice the increase in the air flow from your ducting. Heat pumps produce heat differently; they produce larger amounts of slightly warm air. Traditional means of heating such as wood, oil or electric produce large amounts of heat over a short period of time which gradually diffuses into the home. The heat produced by a heat pump will be much more even by its consistent process; this method helps eliminate hot or cold spots in the home and evenly heats the conditioned space. You will need to balance your system after each season of
operation. This is performed in the summer by closing registers in the cooler rooms downstairs, allowing cold air to reach the upper levels of a home. In the winter, closing registers in warmer rooms upstairs, allowing warm air to reach the lower levels of the home.
Why is my indoor fan running but my heat pump is off?
Heat Pumps are designed to extract every bit of available heat in order to attain maximum efficiency. When a heat pump shuts off, the indoor unit still has a residual amount of heat stored in its coil – by blowing the air over this, all stored heat is taken out of the coil.
This energy saving feature is enabled when the fan is set to “Auto” mode. In addition, the fan can be set to run continuously in the “On” mode creating perpetual airflow through the ductwork, and to better mix air in the home providing more consistent temperatures.
Why is my Heat Pump steaming large plumes?
When it’s very cold outside and a defrost mode is activated, the system may produce steam. Usually it starts and ends with a flushing sound of refrigerant. This is a normal process; your system is clearing the frost from the outside unit in order to continue being efficient.
Why is my Heat Pump thermostat displaying aux/auxiliary heat?
When a system is in defrosting mode, the electric backup within a system (ducted heat pump) will activate in order to compensate for the pause in operation. The outdoor temperature limit of your heat pump could also be reached. Every heat pump has an outdoor temperature limit, where the system can no longer produce heat efficiently. When this occurs, the system will switch to the electric backup heat to avoid wear and tear on the unit, and continue providing comfort without a drop in temperature. We recommend at -15°C that all systems be shut off, and auxiliary heat activated (with the exception of our cold climate heat pumps), this will assist the lifespan of the unit as it works hardest during colder temperatures. This will also maintain efficiency of the unit, as at this temperature the cost of opera;on is the almost the same as electric backup.

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For E.T. phone 506-444-HOME (4663)