Air source heat pumps (ASHP) are electric appliances that provide heating and cooling by moving heat into a building (for heating) or out of a building (for cooling). Heat pumps do not create heat like electric resistance heating or fossil fuel-fired heating systems; instead, they transfer heat from the one place to another. ASHPs use the outdoor air as a source of heat.

They accomplish this by using a refrigerant that absorbs heat from colder air in order to move that heat into a space with warmer air—much the same way that a refrigerator or air conditioner works except that it can move heat in both directions to provide both heating and cooling.

Since it takes far less energy to move heat than it does to create heat, ASHPs are one of the most efficient home heating systems available.

Ductless air source heat pumps are exactly as they sound: heat pumps that don't require that you have ductwork in your home to provide heating and air conditioning. Each ductless system includes one outdoor condenser unit connected to one (single-zone) or more (multi-zone) indoor wall, floor or ceiling air distribution units. Ductless ASHPs are often referred to as ductless mini-splits.

Ductless air source heat pumps are the most efficient air-source systems and can be installed as a primary source of heating and cooling or installed to supplement existing systems. These supplemental applications could include, for example, installing ductless units in the most frequently used rooms like family rooms or master bedrooms to displace heating or cooling from your existing system or placing ductless units in rooms or new additions that never seem to be warm or cool enough.

These systems often come with remote controls that allow you to use them for heating, cooling, dehumidification or as a ceiling fan. Because each indoor unit can be controlled individually, you can reduce your energy use even more by lowering the temperature in rooms that are not being used.

Ducted air source heat pumps have an outdoor condenser unit that is connected to a building's ductwork, which is used to distribute heating or air conditioning throughout the building. Ducted (also known as central or unitary) ASHPs are not much different from central air conditioners or furnaces, except that they provide both heating and cooling in a single system. Ducted ASHPs can work with your home’s existing ductwork, though some modifications may be necessary to adapt it from being suited for a furnace to being suited for a heat pump.

Regardless of whether a system is ductless or ducted, all ASHPs will have an outdoor condenser unit (pictured below), which will be mounted on a ground platform or on the side or roof of your building (to avoid snow buildup). This outdoor condenser unit will be connected to one or more indoor air distribution units. If you’re installing a ducted ASHP, this will be a central air handler similar to one used by a furnace or central AC system. If you’re installing a ductless ASHP, this will typically be a wall-mounted unit (see below).

Above: A ductless ASHP condenser and indoor unit; Below: A ducted ASHP condenser

For homeowners that might not have suitable wall space or don’t like the aesthetic look of the wall-mounted indoor unit, floor-mounted and ceiling-mounted units are also available, though these units cost more to install. _{Photo courtesy of E. Armstrong}

High-efficiency heat pumps not only cool and heat, but also purify indoor air and improve the comfort of your home. There are many reasons why an air source heat pump could be a good fit for your home and needs:

• High-efficiency heating and cooling. Heat pumps provide both your heating and cooling capabilities in one unit. Modern high-efficiency heat pumps are as efficient as top-tier central air conditioners and 2-4 times more efficient than traditional electric heat.
• Enhanced home comfort. Heat pumps give you more control over the comfort levels in your home. Ductless heat pumps can be installed in individual rooms or zones of your home so you can adjust the temperature throughout your home based on your personal needs.
• Health. Burning natural gas (methane) inside our homes can create indoor air pollution. High-efficiency electric heat pumps not only eliminate the risks of these pollutants, but also provide air filtration and humidity control to purify the air in your home.
• Flexibility. Heat pumps are a flexible technology that can provide heating and cooling to buildings of all shapes and sizes—regardless of whether you have ductwork or not. Heat pumps are a great option whether you want to replace your entire existing system or just want to add heating or cooling to a one or more room(s).
• Lower your carbon footprint. Heat pumps can be powered by renewable electricity like wind or solar. Even with the current mix of coal, gas, and renewable energy powering our electricity grid, heat pumps are a more environmentally-friendly way to cool and heat your home or water. Pair your heat pump with solar and go entirely green!
• Smart. Room-based units can sense and respond cold or hot spots. Many are also controllable from your phone—in the house or remotely. Warm or cool your house before you even get home!
• Quiet. Tired of loud air conditioners or noisy furnace blowers? Heat pumps are often much quieter than traditional heating and cooling systems. Many high-efficiency models will run continuously rather than blasting on and off, reducing disruption to your home.
• Increased resiliency. Efficiently cooling even one room in a home may be a life-saver for people vulnerable to excessively high temperatures during heat waves due to a warming climate.

Air source heat pumps are considered to be “renewable” heating and cooling systems because they do not create heat, but rather they move heat existing in the ambient air into your home. This process is powered by electricity, which can also be generated by sourced from renewable sources like solar, wind, or hydro.

Even though Boulder’s energy grid is only about 30% renewable today (and getting greener every year!), a heat pump system powered by grid electricity will still reduce your greenhouse gas emissions from heating by 20-60%! These emissions will continue to decrease from year to year as the utility’s grid becomes greener, whereas the emissions from fossil fuels will always stay the same.

While heat pumps are a great fit for many Boulder homes, like other heating and cooling systems they have a few drawbacks:

• Performance in extreme cold. Since air source heat pumps rely on extracting heat from outdoor air, the heating output and efficiency of a heat pump declines as outdoor air temperature declines. While high-efficiency heat pumps produce heat down to -13F, you may consider keeping a backup heating system for the coldest days of the year. This could include keeping your existing system in place or adding a supplementary system like portable heaters or electric baseboards. Some centrally ducted heat pumps also have electric resistance backups built into the unit. It is worth noting that it is unlikely your heat pump will stop providing heat entirely: in the last 20 years, Boulder has only had 9 days where the temperature dipped below -10F and only for a few hours at a time.
• Aesthetic considerations. Heat pumps require outdoor (e.g. condenser and piping) equipment similar to a central air conditioner. Ductless heat pumps can also require additional indoor equipment typically mounted on high on the wall. EnergySmart contractors and advisors can discuss a variety of options available to you to minimize aesthetic impacts from a heat pump installation.
• Higher installed costs. Heat pumps can cost more upfront than individual fossil fuel or central AC systems, but if your systems are nearing end of life, "early retirement" and switching to a heat pump could save you more in the long run.

There are few homes where some heat pump solutions might not work. However, if you answer “Yes” to any of the questions below, a heat pump system could be a particularly good fit for you:

• Do you want to reduce your carbon footprint?
• Do you want central air conditioning but don't have (or don't want to) install ductwork?
• Do you have persistent hot or cold spots in your home?
• Do you want more control over the temperature in individual rooms in your home?
• Are you sensitive to air pollutants and allergens?
• Do you heat with electric resistance heating and want to reduce your energy bills?

Heat pumps are typically rated for heating efficiency based on their Heating Seasonal Performance Factor (HSPF) or seasonal Coefficient of Performance (COP), both of which describe the system’s efficiency over the course of the heating season. The seasonal efficiency of heat pumps can range from 220% to 300%+ (i.e. COP of 2.2 to 3.0) depending on the system type and application. That means that for every one unit of electricity used, 2.2 to 3 units of heat are transferred into the home.

By comparison, electric resistance heating has a COP of 1. Heat pumps are even more efficient when used in the shoulder season: if you only use your heat pump when the temperature is above freezing (using your existing furnace for backup for colder days), your system may be 300-400+% efficient!

Heat pumps also provide efficient cooling, comparable to the highest-efficiency air conditioners. Ductless heat pumps can give you the opportunity to get AC throughout your home without using loud window units or installing or /expanding your ductwork!

A heat pump installation is typically a straightforward process with minimal disruption to your home. A simple, single-zone ductless ASHP system can be completed in less than a day and only requires a single 2-3 inch hole to be cut (and later, sealed) in your wall.

If you are installing a “multi-zone” ductless system or a ducted system that requires modifications to your ductwork, your installation may take a few days or more to complete.

While intuitively you might assume that you should install a ducted ASHP if you already have ductwork, there may be plenty of cases in which a ductless ASHP might actually be a better option for your needs. Some examples include:

• Do you have poorly sized ducts or inadequate heating/cooling to particular areas of your home? Ductless systems could help you address those hot and cold spots in a less invasive/costly manner than making significant ductwork modifications.
• Do you have a new addition on your home, or are you planning one soon? A ductless system could be a cheaper solution than extending ductwork to the addition.
• Do you want to add zoning for heating and cooling in your home? An EnergySmart contractor can install ductless units and/or modify your ductwork to give you more control over zoning in your home.
• Is modifying ductwork in your home very difficult (or are you concerned about the invasiveness of ductwork modification) Ductless systems could offer you the benefits of switching to a heat pump without necessitating an extensive ductwork retrofit.

Every home (and every homeowner) is different. EnergySmart contractors can help make a recommendation that best suits your specific needs.

Heat pump water heaters also use heat pump technology to transfer heat from one place to another. Unlike air source heat pumps, which are used to heat and cool the air in your home, heat pump water heaters extract heat from the air and moves it into a tank to heat water. As a result, heat pump water heaters are 2-3 times more efficient than electric resistance water heaters.

As shown in the diagram below, most heat pump water heaters differ from air source heat pumps in that all of the heat pump elements are indoor and combined with the storage tank. Most heat pump water heaters are “hybrid” heat pump water heaters and include electric resistance heating elements to provide backup heating when hot water demand is high.

Energy savings. If you use an electric resistance tank to heat your water, a heat pump water heater will cut your water heating bill in half or more (and reduce your carbon footprint too!). Depending on your hot water usage, this could amount to $200 in electricity bill savings a year or more!

Dehumidification. While Boulder can be pretty dry, humidity can still be a problem in some basements. A heat pump water heater will greatly reduce (or eliminate) the need to run a dehumidifier in your basement.

Noise. Since the heat pump compressor is located inside your home instead of outdoors, a heat pump water heater will be noisier than a typical water heater—more similar to a window air conditioning unit. Speak with your EnergySmart advisor or contractor if you are sensitive to noise and vibration to learn more about your options.

Cooling effect. Most heat pump water heaters extract heat from indoor air. If placed within a finished space, the heat pump water heater will cool off the room it’s in. While installing a heat pump water heater will typically still offer net energy savings, it will increase your space heating bill a bit to compensate—though on the flip side, it will reduce your need for air conditioning in the summer!

Higher upfront cost. Heat pump water heaters are more efficient than traditional water heaters but will cost more upfront than a typical electric water heater. However, their energy savings will pay for the difference in cost--and rebates from EnergySmart will help to offset the added cost as well.

Do you use an electric resistance water heater? A heat pump water heater could be an excellent investment for you if you currently are using an electric resistance water heater. The savings from going from an electric resistance tank to a heat pump water heater and available rebates will offset the added upfront and pay back your investment over the course of several years.

Do you have a partially finished or unfinished basement with enough clearance? Heat pump water heaters are a bit taller than most traditional hot water heaters and need sufficient airflow to operate at highest efficiency. Additionally, they should ideally be placed in an unfinished space to maximize the amount of heat extracted from the ground and not from heat provided by your heating system. If you have enough space next to your furnace, a heat pump water heater will be able to take advantage of the waste heat generated by your furnace.

A free site visit from an EnergySmart contractor can help you figure out whether a heat pump water heater is right for you. Get started today!

A variety of rebates for air source heat pumps and heat pump water heaters may be available from Boulder County, the City of Boulder (for city residents), and through your utility. As these incentives are all available on a first-come, first-served basis, the best way to find out what incentives are available is to speak with an EnergySmart Advisor.

Elevations Home Energy Loans are available to help with financing ASHP installation and purchasing. EnergySmart and Elevations Credit Union are working together to offer you these loans that can help you attain a more efficient, comfortable, and affordable home.

Interest rates start as low as 2.75%. Loans can be paid in part or in full with zero prepayment penalty. Home Energy Loans can also be combined with rebates to fully fund your home upgrades. This exciting financing is available to residents throughout Boulder County communities for qualified energy efficiency and renewable energy projects in existing buildings.

Pricing will vary depending on your home and your needs: the cheapest air source heat pump applications start at around $4,000 before rebates (e.g. a single ductless unit for a large zone in your home). Heat pump water heaters typically start at around $2,500 before rebates.

Comfort365 is a partnership between the City of Boulder and Boulder County’s EnergySmart Program to provide residents with a cleaner, more efficient, and comfortable option to cool and heat their homes. Using EnergySmart’s established one-on-one advising model, Comfort365 pairs interested residents with their own personal expert advisor for free! Comfort365 helps residents to explore options for heating and cooling with renewable energy in their home, connect with contractors, evaluate bids and get access to any and all rebates available for your exciting project.

EnergySmart is Boulder County's one-stop shop service to help residents make their homes more comfortable, affordable, and environmentally friendly—benefitting both people and the planet! EnergySmart was started in 2011 and has engaged over 17,000 homes in Boulder County, been replicated across the country, stimulated over $31M dollars in local investment, and reduced almost 14,000 metric tons of CO₂ annually. EnergySmart is managed by Boulder County Commissioner's Sustainability Office and implemented locally by CLEAResult.

The City of Boulder's Climate + Sustainability Division works to pioneer pathways and foster collaborative actions that achieve sustainable energy and resource use in our organization and community.This work includes reducing the amount of energy we use in Boulder through energy efficiency efforts, and identifying local, renewable sources to improve community resilience and energy sustainability.

Comfort365 works just like any other program of EnergySmart—just focused on renewable heating and cooling.

• Personal Energy Advisor. Have questions about how to be more comfortable in your home, how to save money, or who to work with? Your personal energy adviser will answer all these questions and more.
• Access to Rebates. Save money by taking advantage of any and all EnergySmart, utility, and manufacturer rebates!
• Connect with Contractors. An expert EnergySmart Advisor can help you collect and understand bids from our pre-qualified contractor list.

Fill out the form here, call Monday to Friday between 8:00am-4:30pm at 303.544.1000 or email any time at to get started!

There are hundreds to thousands of dollars of rebates available through EnergySmart for heat pumps and other home energy improvements. However, these rebates are only available on a first-come, first-served basis. Get started today to make sure you can take advantage of these rebates.

More broadly, electrifying your home is one of the big steps in supporting our community’s shared efforts to reduce our climate and environmental impacts. Boulder is helping to lead efforts to accelerate our transition off all forms of fossil fuels and you can inspire others to take this important step.