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Heat pumpAbout half of the homes in Washington Grove already rely on heat pumps to at least partially heat and cool their homes and 75% of new homes in the county are now built with them. Some Grovers are considering switching their primary heating from boiler/radiator systems to heat pumps. The Sustainability Committee enthusiastically encourages making this switch.

To help people who are considering this investment, we have prepared a series of Q&A’s about switching to heat pumps. This month, we focus on supplementing or replacing a piped hot water system that uses radiators or baseboard hot water and fuel oil or propane as the heat source. In upcoming months, we will address switching to geothermal systems and mixed systems.

A heat pump works the same way as an air conditioner or refrigerator for cooling, but also in reverse for heating.  By condensing and evaporating a refrigerant gas within the system, a heat pump actually “moves” heat to or from the living space as needed rather than generating the heat itself. Overall, the system is two-to-three times more efficient than an oil furnace, though the efficiency decreases somewhat if outside temperatures become more extreme.

For houses that have both a hot water (hydronic) heating system and a centrally ducted air conditioning system, it would make sense to first consider a central air heat pump if the ducts are sufficient to serve the house with heat as well as cooling, which is true in most cases. See this link for advice on those central heat pumps: Switching Your Home Heating from an Oil or Propane Furnace to a Heat Pump.

For houses that do not have central ductwork, the most common type of heat pump currently on the market is called a mini-split.  It can be installed to replace most of the heating load and all of the cooling load as a supplement to your radiators where you need to.

There are some new heat pump systems that can supply hot water directly to your hydronic system but are not yet in common use.  There are also systems that utilize very small ducts that can retrofit old houses that do not have ducts. If you are interested in pursuing this type of system, see question 11 below.

The Committee cannot make specific recommendations for Grove homes as every home has unique conditions, but we can help get you started by addressing some questions you may have.

1. How will the new system work?

Minisplit heat pumps can serve either one room or zone or several rooms and provide both heating and cooling.  There are one or more outside units that contain one or two condensing units and are connected by small piping to one or more inside units that usually mount high on the wall.  There are also inside units that mount below windows and units that mount in the ceiling.  The ceiling units can actually have ducts that supply other rooms, if that works in your house.  Most of the mini-splits stay efficient to exterior temperatures below 0°F! The temperature remains above 13° for 99% of the year in this area. Mini-splits have their own thermostats so you can control the temperature of each zone or room. The most efficient way to use it with your hydronic system is to set the existing system to several degrees less than you set the heat pump to so that the heat pump supplies efficient, clean heat most of the time, and the radiators kick on if the heat pump can’t handle it alone. If you have smart thermostats, you can customize or even integrate the settings to fit your situation throughout the day. This will minimize your fossil fuel use.

2. How will the switch benefit me?

Heat pumps are much more efficient than any other system because they are only moving heat rather than generating it. High-end oil and propane boilers can approach 100% efficiency at producing heat from their fuel. Heat pumps are more efficient and can produce 3-4 times as much heat as the electricity they use. In Maryland, the average lifecycle savings for converting to heat pumps from oil or propane range from $4000 – $8000, depending on:

  1. how much you decide to minimize the use of the back-up radiators, and
  2. where fluctuating fuel costs end up.

Reducing or eliminating the burning of oil or propane also reduces or eliminates the risk from the by-products on the indoor environment such as carbon monoxide, nitrous oxide and soot, and of course the risk of fire.  Two added benefits of a high-efficiency heat pump are more efficient cooling, which will be increasingly important as climate change raises temperatures in our already hot, humid climate, and more stable electric prices as future fossil fuel cost increases.

3. How will the switch benefit the environment?

A heat pump that relies on electricity from a standard energy mix on our grid will emit only one-sixth of the greenhouse gases that come from an oil or propane boiler—an enormous improvement.  Better yet, if you have a renewable electric source, such as community solar, the emissions drop almost to nil. Overall, the more fossil fuels we leave in the ground the more manageable will be the changes we must make to avoid severe climate-related problems.  An additional benefit to the community is reduction of the secondary combustion particulates and gases spread into the air around us by an oil or propane boiler.

4. What physical changes will happen in and out of my house?

One or more compressor or “outside units” will be placed next to the house on the side adjacent to where the inside unit will be. A pair of insulated copper tubes containing the refrigerant will be run – attached to the exterior wall (or if accessible, within the stud space) – to a penetration point at or near the inside unit. This tubing along with a plastic condensate tube and the wiring will be covered with a plastic case.  The “inside unit”, or air handler, is a small, usually wall-mounted cabinet positioned to blow the warm or cool air throughout the room.  These units generally have adjustable louvers that may be motorized to help better distribute the conditioned air.

You could position one inside unit for each commonly used room or use a ducted unit to distribute the conditioned air to several rooms. The number of outside units can be equal to the number of inside units; or two units can be housed in the same outside cabinet; or one larger outside unit can serve multiple inside units.  You will need to carefully consider where you place both inside and outside units, based on both performance and how they look.

Conducting an energy audit of your house will help you get the properly sized heat pump (see question 9 below). Following the insulation and air-sealing advice provided by an audit will result in smaller or fewer units and a more comfortable house.  If you completely replace the existing system, the contract will include removal of the old oil or propane tank, piping, and any residual fuel left inside, as well as touch up interior finishes where the radiator system is removed.

5. What is the likely cost range for a new system?

As mentioned, most of the mini-splits are extremely efficient at all outside temperatures, even those in Maine or Minnesota, so there are no quality issues to navigate.  Each of the simple two component systems cost between $3000 and $5000, so installation for the whole house can run approximately $10,000.  Installation is usually fairly simple, as described above, but there may be some touch-up finishing required where the tubing lines are run.  The existing radiant system can provide the back-up.

6. How long does it take to install a new system?

The installation of a single simple system can be done in one day, so if there are multiple systems, it could take several days, also depending on the exterior and interior touch ups.  It is best to plan ahead so that you are not left in the middle of the winter with a possibly broken oil system, forcing you to make rushed decisions in cold weather.

7. What maintenance will the new system require?

Very little. The system includes filters that will need to be changed in each inside unit, but unless there is refrigerant leakage, there are no real adjustments to be made or burned-out elements to replace. And because there is no combustion, there is no clean-up of soot.

8. How long do heat pumps last?

Like air conditioners, they last 15-20 years. This is similar to current gas boilers but many of us in town have ancient oil boilers that have lasted decades. Unfortunately, these old boilers are very inefficient both in the amount of oil they consume, how much of the heat value gets to the house, and how much of it goes up into the atmosphere.  The Energy Star Homes program recommends replacing systems every 10 years to take advantage of the ever-increasing efficiencies. In fact, if you currently have an older model heat pump, it is likely much less effective at low temperatures than current models. Energy Star records the efficiencies of all units submitted and raises the standards every couple of years.

9. How do I get started in making the change to a heat pump?

Rather than using the size of your existing boiler, which likely was oversized in the era of cheap oil, the best first step is to conduct an energy audit of your house and a load calculation to determine the correct size of the units you need.  An audit will also help to ensure the comfort of your home once the changes are completed. Next steps should be discussions with two or more contractors with experience installing high-efficiency systems, a site visit, load assessment, and a request for cost estimates for various options.

10. Are there people in town who can talk to me about this?

We are planning on getting small groups of interested residents together to share our experiences and discuss the more detailed aspects of each type of conversion. If you are interested, please let Bob Booher know, and we will set up a meeting with other Sustainability Committee members and residents such as Gary Temple, who have useful experience.

11. Are there systems that can work directly with my existing radiator system?

There are both air-to-water and water-to water heat pumps that can provide hot water to the heating system, domestic hot water, or both. Because your existing system was designed around hotter water, careful modifications to the existing system are needed to make sure sufficient heat is delivered. If you already have ducted air conditioning, the heat pump can be integrated into both. More on this in a subsequent article.

12. Can you recommend any websites that will tell me more about this technology?

Yes, here are a few that may be helpful:

13. Can I get any rebates, tax credits, or loans to help pay for a heat pump?

There are a variety of financial support offers but they are currently in flux due to the Infrastructure Act and the Inflation Reduction Act (IRA). Here is a good summary. 

It’s best to research this question at the time you purchase a heat pump.  Meanwhile, here are the sites to watch:


Federal Tax Credits

Loans (Maryland)

  • Clean Energy Advantage Loan Pilot Program for “high efficiency equipment.”
  • BeSMART Energy Efficiency Loan for Homeowners, including ENERGY STAR heating and cooling systems.


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