How Does the Outdoor Temperature Affect the Performance of my Heat Pump?

So many of our customers ask us just how cold their heat pumps will operate at. In other words, how low can the temperature get before their heat pump stops working and backup heating sources, like electric baseboards, oil hot water baseboards, or oil forced hot air are needed?

To answer that question, you’ll need to understand how they work. Most brands won’t actually shut off at a certain temperature. Instead, they’ll continue to work, although at a lower efficiency rate. Some will shut off for safety reasons at certain low temperatures, but this is by no means an across-the-board feature.

Understanding Rated Outdoor Operating Temperature

All heat pumps have a rated outdoor operating temperature, which is the minimum temperature that the device will operate safely at.

As it gets colder outside, the heat pump can extract less heat from the ambient air, requiring more electricity to generate the quantity of heat (BTUs) it would at a warmer temperature. This means that the heat pump will require much more energy to produce the heat needed to heat your home.

While it’s important to know the outdoor rated low temperature of your heat pump, the more important question to ask is how much heat (in BTUs) does it produce at that outdoor rated low temperature? And how does that compare to competitor models?

Comparing Heat Production at the Rated Outdoor Temperature

Compare the 12,000 BTU rated models below. Each of the pumps listed produce at least 9,000 BTU at the nominal heating temperature. However, you can see that their heating capacity drops at low temperatures from the row entitled “heating operating range with BTU/h capacity.” You’ll see that several of the units produce only half the heat they do when operating at warmer temperatures.

For example, the LG Prestige is rated at 12,000 BTU, and at a warmer temperature of between -5° to -8°the unit will produce around 13,000 BTU, which is great. Anything above the rated 12,000 is fantastically efficient. However, at its rated outdoor operating temperature, -25°, the LG Prestige will put out about 9,000 BTU, which is well below its nominal output of 13,000.

A comparable model, the Fujitsu RLS3H, is also rated at 12,000 BTU. At the warmer temperature of between -5° to -8°, the Fujitsu produces over 15,000 BTU, well above the rated 12,000, which is fantastic. The Fujitsu’s rated outdoor operating temperature is -26°, and at that low temperature, it still will produce around 12,000 BTU, which is incredibly efficient.

Upfront Costs and Lifetime Savings

While a lower-quality heat pump may cost far less upfront, you will also see a reduction in energy savings over the lifetime of the pump. This is especially true if the pump in question produces a very low percentage of its nominal heat rating at that temperature or does not operate at low outdoor temperatures.

Having a heat pump that does not operate efficiently at low outdoor temperatures means that your backup heating system will need to be turned on more often to keep your home warm–and that means that you won’t get to enjoy the higher percentage of savings that a higher-quality unit would be able to provide.

Both the LG Prestige and the Fujitsu RLS3H heat pump models are fantastic products from great brands and are worth considering. Both units operate at low temperatures, produce a high quantity of heat at those low temperatures, and offer great warranties.


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