Renewable Heating

Why is renewable heating important?

Heating is the largest residential use of energy in the northeast, with 56 percent of home energy consumed for space heating. There are two important concerns related to this energy use: its cost and carbon emissions. The average New York household spends nearly $2,500 on heating annually. There is room for savings for almost everybody regardless of the heating system your household uses. Certain systems and fuels are more efficient than others, and require less energy to produce heat.

Residential heating is not only costly for New Yorkers, but also produces a significant portion of our state’s residential greenhouse gas (GHG) emissions. But this varies dramatically based on the heating system and fuel used. Fossil fuels are much more carbon intensive: Fracked natural gas produces 63 pounds of carbon dioxide equivalent emissions per therm (1 therm = ~100,000 BTUs), and coal produces 4,631 pounds per short ton. (Note that there are different methodologies used to calculate these figures which may result in some variation.) Using electricity from renewable sources for residential heating releases no carbon emissions.

This creates an opportunity for the elimination of household fossil fuel use so that your home can become a net-zero home. Net zero homes are carbon neutral, meaning that they do not produce any net carbon dioxide emissions, significantly reducing the residents’ carbon footprint! Net-zero homes are efficient, and heat and power their homes with renewable energy. In many cases, they can also help you save money on your utility bill.

What are the different types of renewable heating?

The major types of renewable heating are heat pumps, both ground- and air-source, and biomass, which include stoves and boilers powered by wood or wood pellets. A discussion of each of these is included after the summary table below:

Heat Pumps

Heat pumps are one renewable heating option that can reduce your energy bill and carbon footprint. Simply put, heat pumps move heat from outside into your home in the cold months, and move heat out of your home when it’s warm using electricity and refrigerants. Although the term ‘heat pump’ may sound unfamiliar, you already have heat pump technology in your home: your refrigerator uses heat pump technology to maintain its cold temperature, even in a warm environment!

There are two main types of heat pumps, ground-source heat pumps and air-source heat pumps. Air-source heat pumps are more common, with 85% of residential heat pumps in the U.S. being air-source, and is what is used in the PowerHouse.

Air-source heat pumps transfer heat from outside to inside the house using refrigerants, and can extract heat from even cold air on a winter day! Here’s how the magic works: During cold months, the liquid refrigerant is at a very cold temperature when at low pressure (see the bottom left of the drawing in Heating Cycle), say -20 degrees F. As it passes through the outdoor coil (top left), air is blown over it. Let’s say the air is at 0 degrees F. The refrigerant will be warmed by that air, and say increase to only -10F, an increase in temperature that will turn it into a vapor. It then passes through the compressor, where its pressure is increased significantly. As you may recall from a high school science class, when you increase pressure, temperature increases, and our refrigerant’s temperature shoots up somewhere closer to 110 degrees F. It then circulates inside the house through the inside coil, where air is blown over it, releasing some of its heat. As it releases the heat, the gas condenses back into a liquid, and say cools down to 100 degrees F. It is still under high pressure until it passes through the expansion device, where its pressure is released, and its temperature drops again to say -20 degrees F, and it can do the whole cycle over again. Check out this video from “This Old House” for additional explanation of how air-source heat pumps are able to draw heat from the outdoors, even on very cold days.

In summer, the the reversing valve is used to reverse the process, and heat can be taken from inside the house and moved outside, thus providing cooling. Magic!

With air-source heat pumps, heat can be distributed through the house either through using a system of ducts or through a ductless system, also known as a mini-split. The PowerHouse has a minisplit system, with an outdoor unit and the indoor unit connected by thin lines of refrigerant that transports the heat from one side to the other. Minisplits are highly modular, and can work well for all sorts of home configurations—from very small ones to large ones with many rooms.

A ground source heat pump uses an underground heat exchanging ground loop and electric heat pump to exchange heat between your home and the earth. The earth’s underground temperature generally stays around 55 degrees. In the summer, this underground temperature is cooler than that of the household. During this time, a refrigerant which can absorb and transport heat circulates from your home to the cooler underground, and back through the ground loop piping, which cools the house. In the winter, the heat from the ground is transferred to the cold home using this same liquid in the ground loop piping. Many businesses and residences in Ithaca, such as the Ithaca Youth Bureau, Argos Inn, Cornell Cooperative Extension of Tompkins County, and Purity Ice Cream already use heat pump systems.

The image above shown an example of a closed loop ground source heat pump system, which represent the most common installation. An open loop ground source heat pump system connects directly to a pond or well and uses this body of water for the heat transfer process. Open loop systems usually cost less to install and can be more efficient, but are dependent on available water supplies. In addition to open and closed loop systems, there are also vertical and horizontal installations. Most residential homes use horizontal installation as it more cost efficient than vertical installation. However, horizontal installation does require more land, and vertical installation requires less land and is better for larger scale operations. The video below explains these various options in a little more detail.

While ground-source heat pumps systems tend to require a significant upfront investment, the savings from lower energy use will tend to pay for itself over time. In addition, there are state and federal incentives to lower the price of installing ground source heat pumps. You can find out more about these rebates on the Get Your Greenback website.

Biomass - Wood & Pellet Stoves & Boilers

Another type of renewable heating is biomass fuel. Biomass fuel is the burning of organic materials, usually wood. While the burning of biomass does release carbon, it is still cleaner than fossil fuels, often cheaper, and usually has local origins which can help stimulate local economies. Biomass heating can still be considered a carbon neutral energy source because the plants used as biomass captured an equivalent amount of carbon dioxide during photosynthesis while they were alive. If the wood is harvested sustainably, with trees that absorb carbon replacing those that were cut down, then there is no net carbon impact from this burning.

However, some wood stove biomass systems can still be quite polluting, releasing carbon monoxide and other emissions, such as particulates that can cause respiratory illness. These emissions can be significantly reduced through improved technology and maintenance practices, such as burning dry wood, and burning at a hot enough temperature. Wood pellet systems are generally cleaner and more efficient than wood stoves. While wood stoves have increased in efficiency over the last few decades, they still can be a source of air pollution. Since pellet stoves are automated, pellets are at the right level of dryness and there is a controlled, efficient burn. Pellet stoves burn compacted pellets of wood waste, such as sawdust, low quality trees, or even other organic material like nutshells.

Pellet boilers are also available that can replace a fossil fuel boiler. These boilers are highly efficient and cost much less to operate than fuel oil or propane.

What are the next steps for renewable heating?

When purchasing a renewable heating system, make sure that you are choosing the option that best fits your household. You can find a list of local installers on the Get Your GreenBack website, where you can also find a list of incentives and rebates for renewable heating systems for which you may qualify. If you have any additional questions or would like free support from a trained Energy Advisor, contact us.

And remember, if you haven’t already, we highly recommend getting an energy audit to reduce any air leaks and make sure you have adequate insulation. This is so that any heat that you are producing does stay in your home, and may allow you to buy a small, less expensive system. Learn more about energy audits at the Air Leak page and exhibit.

Q & A

1. I’ve heard that refrigerants used in air-source heat pumps can leak, and that they are really potent greenhouse gases. Is this a concern? Yes, this is a real concern. However, several studies have concluded that the environmental benefits of highly-efficient heating and cooling exceed the costs from occasional leakage, and there are ways to reduce leakage. Read a January 2021 article on reducing refrigerant leakage here (PDF).