Upgrading an A/C to a heat pump: a good idea for many
Does your home have a central air conditioner that you're planning to upgrade? If so, a heat pump could actually cost less after incentives and save money on operating costs.
At first glance, an air conditioner and a heat pump system don’t look very different. A/C systems and heat pumps are both available in mini-split and central ducted configurations, and the interior and exterior components for them often look identical.
But they aren’t the same. Heat pumps, as the name implies, can both heat and cool your home, while an air conditioner is only able to supply cool air. However, most homes in the United States have heating systems, even if you live in a warm climate and need heating only a few weeks out of the year.
If you have an existing air conditioner or you’re thinking of installing a new system, this leads to a common question that homeowners have: is it better to install a heat pump or air conditioning system? (Keep in mind that we’re only talking about central ducted or mini-split systems. Both heat pumps and A/Cs are available as window units, but they have poor efficiency so many of the points discussed in this article do not apply.)
While heat pumps are often a little more expensive upfront than an A/C, current incentives can reduce or even eliminate the cost difference. This can mean that there is little reason to not choose a heat pump system.
However, if you’re new to heat pumps, you probably have a lot of questions about whether it’s better to stick with an air conditioner or upgrade to a heat pump. This article will hopefully answer some of those questions and help you make the right decision for your home.
What’s the difference between a heat pump and an air conditioner?
The key components of a heat pump and an air conditioner are the same, and consist of a pair of heat exchangers, a refrigerant loop, compressor, and expansion valve. Most residential heat pumps and central air conditioners are split systems, which means that two heat exchangers are split into indoor and outdoor units. This is in contrast to packaged systems, which put all of the components into one unit. Window air conditioners are a type of packaged system.
Both heat pumps and air conditioners work on the same principle: they use the refrigeration cycle to move heat from one place to another. This is the same way that your refrigerator works.
The key difference with a heat pump is that the refrigeration cycle is reversible. This means that a heat pump can take heat from inside and dump it outside to cool your home, or take heat from outdoors and move it inside to warm your home up.
The main component responsible for this feature is called a reversing valve. It’s a copper component with 4 ports and a solenoid valve that controls the flow of refrigerant in the system. Here’s an example:
In heating mode, the refrigerant absorbs heat from the outdoor heat exchanger then travels to the indoor heat exchanger where the blower can extract that heat into your living spaces. In cooling mode, the reversing valve changes the direction of the refrigerant flow, so that the indoor heat exchanger takes heat from your home and the blower at the outdoor heat exchanger dumps that heat outdoors.
Selecting heating or cooling mode for a heat pump is done by the thermostat. Smart thermostats can automatically switch between modes as needed, or you can configure it manually.
There are other design differences between a heat pump and A/C. For example, a heat pump has different metering devices that control the pressure and flow of refrigerant in the system. However, the reversing valve is the key piece that allows a heat pump to both heat and cool a home.
Is a heat pump more efficient than an air conditioner?
A heat pump operating in cooling mode is functionally the same as an air conditioner. It’s a common misconception that a heat pump is more efficient than an air conditioner, but all other things being equal, a heat pump will have the same energy efficiency as an air conditioner.
If you’re not familiar with heat pump terminology, now is a good time to get acquainted. Both A/Cs and heat pumps use a measure called SEER2, or Seasonal Energy Efficiency Ratio, to describe the efficiency of the unit in cooling mode. (It’s called SEER2 because it’s the latest version of the standard and provides a more accurate measure than the older SEER standard.)
It’s calculated as the ratio of the BTU output of the unit to the electricity it uses:
SEER = total cooling BTUs ÷ Watt-hours consumed
This means that a higher SEER2 number indicates higher energy efficiency. If you’re looking to purchase either a split-system heat pump or air conditioner, you’ll want to look for one with a SEER2 rating of 16 or better. This rating indicates good efficiency and will qualify the unit for the federal Energy Efficient Home Improvement Tax Credit. For heat pumps, this tax credit is worth 30% of the total project cost up to $2,000 1 or up to $600 for an air conditioner 2.
The highest SEER2 rating you’ll see in either a heat pump or air conditioner is about 22. Models at this level of efficiency will have advanced features such as variable speed fans and compressors.
This will let you compare different equipment from different manufacturers: an A/C and a heat pump with the same SEER2 rating will have similar efficiency. If you look at the product lineup of a manufacturer, you’ll typically see similar product names for their heat pump and air conditioners. For example, Carrier has three product lines for both their heat pumps and air conditioners: Comfort, Performance, and Infinity. Models within each of these product lines will have similar performance – though possibly not exactly the same, because manufacturers may have different product cycles for their heat pumps and air conditioners.
The bottom line is that heat pumps aren’t intrinsically better at cooling than an air conditioner, and you should consult the manufacturer’s specifications to find out the performance of any heat pump or air conditioner.
(Side note: SEER2 is measured at an outdoor temperature of 95°F, but different equipment can perform differently at different temperatures. This means that two heat pumps with the same SEER2 rating can perform differently when operating outside of 95°F. Some heat pump manufacturers will provide a graph of the Coefficient of Performance at different temperatures, especially for cold climate heat pumps. COP graphs are a topic for a different article, however.)
Upfront cost of heat pump compared to air conditioners
Heat pumps are a little more complex than air conditioners, and that fact is reflected in the price. However, the price difference can be small. According to HomeAdvisor, the installation cost of a heat pump ranges between $4,233 and $7,889, with the average being $6,061. The cost of a central air conditioner is slightly less, with a range between $3,884 and $7,937 and an average cost of $5,910.
Those are wide ranges, so you could find that a heat pump system does cost substantially more than an air conditioner with similar specs.
However, one important point is that the federal tax credit for energy efficient heat pumps is worth up to $2,000, while the tax credit for air conditioners is capped at $600. This means that a heat pump could easily cost you less than an air conditioner. Essentially, you would be getting the heating function for free.
As is always the case with any large home project, you should get quotes from multiple contractors. This will give you the opportunity to get different equipment and price options, as well as interview the contractors to find the one you are most comfortable with.
The operating cost of heat pumps, air conditioners, and electric heating
Heat pumps and air conditioners with similar SEER2 ratings will have the same operating cost during the cooling season. (This assumes that other factors that affect the total power usage of the system are the same, including the blower motor and quality of airflow through the ducts.)
However, if you’re replacing an older central air conditioner with a new heat pump, you can certainly expect higher efficiency. This is especially true if the air conditioner is older than 2015, when new federal efficiency standards went into place. According to Energy.gov, replacing a 10 year old air conditioner with a modern unit can save you between 20% and 40% on cooling costs 3.
That’s just on cooling. If you switch to a heat pump, you’ll probably save money on heating too. If you are replacing other types of electric heating, such as baseboard heaters, electric wall heaters, an electric furnace, or portable space heaters, you will definitely save money on operating costs.
This is because electric resistance heating uses a coil to turn one kilowatt-hour (kWh) of electricity into 3,412 BTUs of heat. However, a heat pump moves heat from one place to another, which is much more efficient. On average, a heat pump will generate 2-5 times as much heat as an electric resistance heater using the same amount of electricity.
If you have an electric furnace with existing forced air ducts and you also need to replace your air conditioner, it’s really a no-brainer: switch to a heat pump. You’ll save money on both heating and cooling, and the federal tax credit will give you up to an additional $2,000 in savings.
Comparing the operating cost of a gas furnace and a heat pump is more complicated, and will be the topic of a future article.
Which will last longer: an air conditioner or heat pump?
In theory, a heat pump will have a shorter operating life than an air conditioner because it is working for both heating and cooling. Longer operating times means greater wear on mechanical components like motors and belts.
However, in practice, this isn’t something that a homeowner should worry about too much as long they perform regular maintenance on their systems. Heat pumps and air conditioners generally come with 10 year warranties, but you should expect that a well-maintained system will outlast the warranty.
In other words, if you’re upgrading from a central air conditioner or you’re adding a heat pump to retire a conventional electric heating furnace, the savings in lifetime operating costs should more than make up for any small incremental capital cost (ie. earlier equipment replacement cost) associated with the greater usage that a heat pump system experiences.
Yearly maintenance is recommended for any heating or cooling system, and heat pumps are no exception. Basic maintenance should be performed by the homeowner, which includes keeping the outdoor unit clear of debris and inspecting it for damage, and replacing filters.
According to Energy.gov, professional maintenance should include the following:
- Inspect ducts, filters, blower, and indoor coil for dirt and other obstructions
- Diagnose and seal duct leakage
- Verify adequate airflow by measurement
- Verify correct refrigerant charge by measurement
- Check for refrigerant leaks
- Inspect electric terminals, and, if necessary, clean and tighten connections, and apply nonconductive coating
- Lubricate motors, and inspect belts for tightness and wear
Does a heat pump cool as well as an air conditioner?
The cooling performance of a heat pump or air conditioner is determined by its capacity rating. In North America, this is often expressed in tons, which is a measure that dates back to the days of ice deliveries: one ton of cooling means one literal ton of ice per day.
A more universal measure is British Thermal Units (BTUs). One ton of cooling or heating is equivalent to 12,000 BTUs/hr. Most homes will need somewhere between a 2- and 5-ton heat pump to meet their heating and cooling needs.
As mentioned above, the cooling efficiency of a heat pump or air conditioner is described using the SEER2 measure, with higher SEER2 numbers indicating better energy efficiency. This means that a 3 ton heat pump with a SEER2 rating of 16 will have the same performance as a 3 ton air conditioner with a 16 SEER2 rating. A 3 ton, 18 SEER2 heat pump will have the same cooling performance but use less electricity.
Side note: sizing a heat pump or air conditioner correctly requires an energy analysis
If you’re wondering which type of equipment - a heat pump or air conditioner - will have better cooling performance your home, that’s not quite the right question. It’s the specifications of the equipment - the SEER2 and capacity ratings - that determine how much cold air it will pump out.
Instead, you should always start with an energy analysis of your home. In particular, a Manual J load calculation 4 is a comprehensive analysis that will give an HVAC professional a good estimate of how much heat energy your house gains and loses through the walls, roof, and floor of your building, taking into account your windows, insulation, local climate, and other factors.
You can’t know how much cooling your house needs until you have an estimate of how much heat enters your home during a summer day. That’s what the Manual J calculation will do.
A good way to hire an HVAC company is to ask them to do this calculation for you and make sure their equipment recommendation is based on it. If they refuse or say that it’s not needed, choose another company. Some companies take a lazy, rule-of-thumb approach to sizing equipment based on the square footage of a home. That won’t be accurate, because a well-insulated home will need smaller capacity equipment than a poorly insulated home of the same size.
Bottom line: get familiar with the specifications to understand the cooling ability of a heat pump or air conditioner
Heat pumps and air conditioners are very similar. The key difference is a component called the reversing valve, which allows a heat pump to change the direction of refrigerant flow in the system. This isn’t related to cooling efficiency, so heat pumps and A/Cs will have the same performance if everything else is equal.
If you want to know what kind of cooling performance you can expect, you should understand the capacity and SEER ratings of your equipment.
Finally, if you have a conventional electric furnace and an air conditioner that’s more than a decade old, it will almost certainly be a good idea to upgrade to a heat pump with a 16 SEER2 rating or better. That’s because a new heat pump will save you on operating costs for both heating and cooling, and the federal tax credit will offer additional savings of up to $2,000. Because of this tax credit, it will often be less expensive to purchase a heat pump instead of a central A/C. This gives you heating functionality essentially for free. That’s a great deal!
References
Air Source Heat Pumps Tax Credit https://www.energystar.gov/about/federal_tax_credits/air_source_heat_pumps ↩︎
Central Air Conditioners Tax Credit https://www.energystar.gov/about/federal_tax_credits/central_air_conditioning ↩︎
Energy Saver (energy.gov) - Central Air Conditioning https://www.energy.gov/energysaver/central-air-conditioning ↩︎
Manual J Residential Load Calculation https://www.acca.org/standards/technical-manuals/manual-j ↩︎