Dual Fuel Heat Pumps: Comfort and Efficiency

Even though the worst part of winter is behind us in many parts of the country, we are still getting a lot of questions about dual fuel heat pumps. The main reason: our site focuses on how to buy a new AC and heating system, and all these components are often replaced at the same time. Now that the weather is warmer (and before the first wave of heat arrives) those who have waited to get their system replaced are now looking for ways to lower their utility bills or get tax a credit on higher efficiency HVAC equipment.

Let’s start with a definition: Dual Fuel Heat Pump

A dual fuel heat pump is a heating (A/C can also be combined…) system that relies on electricity and one other source of heat, such as natural gas or heating oil.

Before going further, we should include a bit of history

In the earlier days of heat pumps, they were often used in homes and buildings where a primary fuel such as natural gas, heating oil, or butane was not available. In that case, electricity was the only common option. Most heating was accomplished through the use of a compressor and working fluid (aka Freon or refrigerant). For easier understanding, heat pumps are often described as “an air conditioner or refrigerator in reverse”. That’s easy to understand if you have ever stood behind your refrigerator or outside AC unit. Anyway, in a heat pump the main work of creating heat is powered by electricity. Because they don’t “extract and move” heat very well when the outside temperature drops below a certain point, heat pumps require a secondary or “emergency” source of heat. Before dual -fuel models became available (and still today when electricity is the only energy source), the secondary heat source was resistance or “strip” heating. Nearly everyone has seen this type of heating in the orange glowing part of radiant heaters. The element in these gets hot quickly, but electrical resistance is generally not an efficient way to heat space –they use a lot of electricity for the amount of heat given off.

Because they require the use of a compressor and for other reasons, some might ask

In situations where gas or heating oil is available, why bother with the heat pump…why not just have a high efficiency furnace?

This is a good question, and it makes for lively debate. The quick answer is that, with a dual fuel heat pump, a sensor in the system chooses the mode (electricity powered heat pump OR gas/oil/etc. furnace) that is most efficient for the current temperature, outside conditions and thermostat setting. Here’s an example: in the daytime in cooler or cold season of the year, have you ever been inside your home or office feeling chilly, and walked outside to warmer feeling air? That’s a good example of when a heat pump would likely be more efficient choice than gas. Why burn fuel when you could “move” warmth from the outside with a lower energy equivalent of electricity.

While discussing ways a dual fuel heat pump can be installed, the following scenario was brought up:

Homeowner has a heating system in good condition and high enough efficiency, but their older or inefficient air conditioning unit goes out. If done properly, by a competent installer, a new combo air conditioner/heat pump can be installed and connected with the existing gas or oil furnace to create a dual-fuel option. In our experience, non-standard retrofits such as this require a higher level of skill than the normal installation of equipment that has been designed to work together.

If you want to read more about heat pumps, you can go to the about heat pumps page on this site.

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