AIR SOURCE HEAT PUMPS

You will hear terms like compression cycle and ground loops, companies start to call radiators emitters. This is to make your fairly new technology sound super high tech, to justify the price.

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An Air Source Heat Pump (ASHP) is a low-carbon heating system that extracts heat from the outside air to warm your home and provide hot water. They are highly efficient alternatives to traditional fossil-fuel boilers, typically producing 3 to 4 units of heat for every 1 unit of electricity used (300–400% efficiency). 

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Heat pumps run at a low flow temperate around 45 degrees, so require correctly designed pipework and sized radiators to get the heat from the water into the pipes and into your radiators.

Gas boilers have a flow temperature of around 60 - 65 degrees.

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Heat pumps and the systems required to support the lower flow temperature around the system are not cheap but with a well designed system, the price and installation does not have to be painful.

You will see a huge reduction in your gas bill but your electric bill will go up as it now has to supply power to a compressor and a heating element (for seriously cold spells), so installing a heat pump with solar and maybe a battery is a great idea.​

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How They Work

Heat pumps function like a refrigerator in reverse, using a refrigeration cycle to "move" heat rather than generating it through combustion:

1. Absorption: An external fan pulls outside air across an evaporator coil containing a cold liquid refrigerant. This refrigerant boils at very low temperatures, turning into a gas as it absorbs heat from the air—even in temperatures as low as  or .

2. Compression: A compressor squeezes the refrigerant gas, significantly increasing its pressure and temperature.

3. Heat Exchange: The hot gas passes through a condenser (heat exchanger), where it releases its heat into your home's central heating system (water for radiators/underfloor heating) or a hot water cylinder.

4. Reset: The now-liquid refrigerant passes through an expansion valve, where it cools down and returns to the evaporator to start the cycle again. 

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How They Are Sized

Sizing is the process of matching the heat pump's power output (measured in kilowatts (kW)) to your home's specific heating needs. Correct sizing is critical: an oversized unit will "short cycle" (turn on and off too often), wasting energy and causing wear, while an undersized unit will run constantly and fail to keep the house warm. 

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Key Factors for Sizing:

• Heat Loss Calculation: A professional must perform a detailed survey of your home's walls, windows, roof, and floor to determine exactly how much heat escapes. This is the only accurate way to size a system.

• Property Size & Layout: Larger or multi-story homes require more capacity (higher kW) to maintain comfortable temperatures.

• Insulation Levels: Well-insulated homes retain heat better and can use a smaller, less expensive heat pump. Poorly insulated homes may require a much larger unit to compensate for heat loss.

• Local Climate: In colder regions, a higher-capacity unit or one specifically designed for cold climates may be needed to maintain output when outside temperatures drop.

• Usage Profile: The number of occupants and bathrooms influences the required capacity for domestic hot water production. 

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General Sizing Rules of Thumb:

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