Air-Source Heat Pumps

Heating and cooling in New England can require a lot of energy and money. Being comfortable at home is important, it needs to be affordable.  Fortunately, there have been remarkable improvements in super-efficient heat pumps which can heat or cool depending on the season.  Every home is different, and the right equipment can pay off within a few years in many cases.

Mini-split heat pump

Mini-split heat pump: outdoor compressor

Heat pumps come in several varieties, including ductless mini-splits and multi-splits, and central systems using ductwork.  There are also ground-source heat pumps which use the ground as a heat reservoir, and air-source which use the outdoor air. The latter are often more cost effective for upgrading heating systems. Like an air-conditioner (which is an example of a heat pump) there is a compressor located outside, and one or more air-handlers inside the home.  A key difference is that heat pumps can operate in both directions, heating in winter and cooling in summer.

Mini-split heat pump: indoor blower unit

Heat pumps have been around for years and are widely used in Europe and Asia, as well as warmer parts of the US.  What is new is that several manufactures now make heat pumps that are far more efficient than before, and which operate down to outdoor temperatures below 0°F, making them useful in New England. The CO2 footprint is half that of other heating options.  Read the Cooler Concord introduction to heat pumps for more information.

Considerations:

Whether a heat pump will make financial sense for you depends on several things: the particular system(s) and capacity being considered, the fuel used in your existing furnace or boiler, and the price of electricity and the other fuel.  Of course, the price of heating fuels varies dramatically with time, and future prices are uncertain.

Equipment Cost

For a typical installation, we look at the economics using recent fuel prices (2016) and representative costs for available systems.  The table at right shows the typical efficiency, annual cost and typical equipment installation cost for different heating fuels and systems.  For Air-source heat pumps, equipment costs can vary significantly.  For comparison, we use a standard installed cost of $11,000 (before incentives) for a central ducted system (typically 36,000-56,000 BTU/hr), and an installed cost of $4,500 (before incentives) for mini-split systems, typically 9,000-24,000 BTU/hr, for which you need one system per room to be heated.

Incentives

  • For Concord residents, CMLP now offers an Air-Source Heat Pump Rebate of $500 per Ton (12,000 Btu/hour) of capacity, for cold climate heat pumps.
  • For non-Concord residents, MassSave offers heat pump rebates of ranging from $150 to $1,600 per ton of capacity for qualified equipment, with 0% interest financing. Ask your HVAC contractor or contact MassSaveRebates@efi.org for latest details.

Typical Pay-Back Periods

For a central ducted system, under the assumption that the system being added  will provide 80% of a typical home’s heat, keeping the original system for back-up heat, and using the recent prices (CMLP electricity: $0.144/kWh, natural gas: $1.60/therm, fuel oil: under $3/gal, propane: $3.50/gal) and a $10,000 installed cost after rebates, typical payback periods are as follows:

  • Natural gas: over 10 year payback
  • Fuel oil: about 8 year payback
  • Propane: under 4 year payback
  • Conventional electric: under 4 year payback

So at first glance, the economics for replacing propane or traditional electric resistance heat are very good, and fairly good for fuel oil as well.  Due to the low price of natural gas, it may not make sense to consider heat pumps unless the CO2 emissions reduction or other benefits are compelling.

CO2 footprint of heating fuels

Average CO2 footprint in Tons/year of different heating fuels.

Environmental Benefits

The amount of CO2 released from heating a home depends on several things: the fuel used, which generates CO2 when combusted (or other greenhouse gases in its production, storage and transportation); the efficiency of the heating system; and the heat load which depends on the square footage and how well insulated the home is. Heat pumps use electricity, which also generates CO2, but since it is several times more efficient to move heat than create it, a heat pump has a smaller CO2 footprint than any of the other systems.

In summary, a heat pump system can save over 10 Tons of CO2 per year compared with oil, electric or propane heat, so installing one is among the most significant actions you can take to reduce emissions.

There are numerous other considerations, which will depend on your current situation.  Here we list two benefits and one potential draw-back for some customers:

Other Advantages:

  • Air Conditioning: in hot weather, heat pumps provide efficient air conditioning even in homes without ductwork;
  • Comfort: heat pumps for cold climates modulate the output to match the home’s actual heating load, which reduces temperature swings in the home.

Potential Draw-backs:

  • Aesthetics: For ductless mini-­splits, some may be concerned about the aesthetics of the indoor units. Be sure to ask contractors about the different options available.
  • Noise: Proper attention should be given to where the compressor is located, to avoid noise issues when the system is operating at its full capacity.

Frequently Asked Questions:

A complete set of FAQs on air-source heat pumps can be found on Concord’s ASHP page.

Q: Can air-source heat pumps really work if it’s very cold outside?   A: Yes, but they should be designed for cold climate homes.  Although older heat pumps may only work down to 30 or 40 °F, many current models are rated down to as low as -15°F, with efficiency twice as high as conventional electric.  For a heat pump to work at those low temperatures, it needs to have adequate capacity for the space to be heated.

Q:  Should I use a ducted or ductless heat pump?    A: The answer depends on your home.  A central ducted system (one outdoor unit and an indoor unit) is a good solution for homes with existing ductwork.  Other homes can use ductless mini-splits (one outdoor/indoor unit pair per room to be heated) or multi-splits (one outdoor unit with multiple indoor units).

Q: How can I know which heat pump to buy, with so many choices to choose from?  A: Choose an outdoor/indoor unit pair with a rating from AHRI (Air-conditioning Heating and Refrigeration Institute) down to 5°F, with a Heating Seasonal Performance Factor (HSPF) of 10 or higher.  A certificate of product rating should be provided to you by your HVAC contractor.  It should be an inverter-driven heat pump, allowing it to operate over a wide speed range, to keep your home at an even temperature without much on-off cycling.

Q: Will a heat pump heat my home all by itself?     A: Your heat pump system will be sized for heating, which is larger than one sized just for cooling.  But since its heating capacity falls with outdoor temperature, at some low temperature the home will need additional heat.  You can keep your existing system, or install some electric resistance back-up for the lowest temperature days.

Q: How about geothermal, might that be a better option than air-source heat pumps?  A: Geothermal or ground source-heat pumps are the highest efficiency option, with larger heating capacity than air-source heat pumps.  But they can be expensive to install, costing as much as $30K to dig the well.  Learn more on our ground-source heat pump page.

Resources/Links

  1. Town of Concord information on Air Source Heat Pumps
  2. Department of Energy guide to heat pumps
  3. Northeast Energy Efficiency Partnerships guide to heat pumps
  4. Most HVAC contractors can install heat pumps, but some are more experienced with cold climate heat pumps. Take advantage of independent reviewers such as Angie’s List (angieslist.com), Consumer’s Check-Book (www.checkbook.org) and others.