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Nest thermostat and cold climate heat pumps.

RTM
Community Member

‎04-10-2024 06:17 PM

A new cold climate heat pump and dual fuel propane furnace. Cold climate heat pump setting to -25 C as it can still function down to -30C. However in dual fuel settings the lowest setting is -12C to switch over to alternative fuel, ie the propane. This looses the advantage of the higher capacity cold climate heat pumps and prematurely switches to propane I think.  Question then is does this happen? at -12C or is it smart enough to keep using the heat pump until there is a lowering of the house temp.  Seems to me that the software should allow for the new higher efficienc,;more expensive I might add cold climate heat pumps and allow settings down to -30C

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alejandom
Community Specialist
Community Specialist

‎04-15-2024 05:56 PM

Hi @RTM,

 

You're right, there's a potential trade-off between maximizing efficiency and protecting your home's comfort level with dual-fuel systems and cold climate heat pumps. Here's how it works:

Dual-Fuel System Operation:

  • A dual-fuel system prioritizes the heat pump for efficiency until the outdoor temperature reaches a pre-set limit (the balance point).
  • At the balance point (usually around -12°C as you mentioned), the system automatically switches to the propane furnace for more reliable heating.

Why the -12°C Limit?

There are two main reasons for this limit:

  1. Heat Pump Efficiency: While some cold climate heat pumps can function at lower temperatures, their efficiency drops significantly. Running a heat pump at very low temperatures can use more electricity than using the propane furnace.

  2. Capacity Limitations: Even cold climate heat pumps have limitations on how much heat they can produce at extremely low temperatures. The propane furnace ensures your home stays warm even if the heat pump struggles to keep up.

Does it Switch at Exactly -12°C?

The switch to propane typically happens around -12°C, but it's not an exact cut-off. Some systems might have a buffer zone or consider additional factors like:

  • Rate of Temperature Drop: If the temperature is rapidly dropping below -12°C, the system might switch to propane sooner to maintain warmth.
  • Indoor Temperature: If the indoor temperature starts to fall below the set point due to the heat pump struggling, the system might switch to propane to prevent the house from getting too cold.

 

On the other hand, you can call our customer service line for further assistance.

 

Regards,

Mario.

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