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Caddy Advanced CR Wood Furnace
The Caddy Advanced CR Wood Furnace offers an intuitive and efficient heating solution for your home, with a recommended heating area of 1,000 to 2,500 ft². F...
$8964
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In-Depth Product Guide
Do You Have The Right Furnace?
Staying warm certainly comes with a price. Space heating and water heating account for almost two-thirds of total residential energy usage in the United States and an astounding four-fifths in Canada's colder climate. Switching to LED light bulbs and purchasing Energy Star-rated appliances can undoubtedly help make your home more energy-efficient. However, finding ways to reduce your heating and cooling loads is where real savings start to add up. If you are thinking about replacing your older, inefficient furnace, we outline everything you need to know below.
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By Tobias Roberts, Rise Writer
Mar 20, 2025 · 7 min read
Does a Furnace's Age and Efficiency Matter?
The US Department of Energy says that heating your home uses more energy and costs homeowners, more money than any other appliance or home function. Of course, when outside temperatures are well below freezing, turning off the furnace will quickly make your home extremely uncomfortable. According to some estimates, about 90 percent of homes in the United States are under-insulated and suffer from leaky building envelopes. These common building errors and omissions negatively affect the energy efficiency and thermal performance of any home.
Net-zero or energy-efficiency upgrades or retrofits to existing homes are one way to reduce the energy consumption related to heating your home. For example, passive home renovations can achieve a 75 to 90 percent reduction in overall energy needs. Investing in a smart thermostat is another fundamental strategy for increasing the energy efficiency of your HVAC equipment.
However, suppose your home has an older furnace. Even if your home is well-insulated and has a tight building envelope, you will spend more energy (and money) comfortable in the winter. The US Department of Energy estimates that furnace and boiler systems over 15 years old might have efficiency ratings between 56 and 70 percent. Modern conventional heating systems on the market today can achieve efficiency ratings as high as 98.5 percent.
Besides saving on your monthly energy bill, upgrading to a more efficient furnace is also a great way to cut back on your home's carbon footprint. The vast majority of households across the country continue to rely on fossil fuels for their heating needs. About 48 percent of families rely on natural gas, while less than one percent of homes rely on electric heat pumps. Does your home depend on fossil fuels like natural gas for heating? If so, the most efficient furnaces on the market can drastically reduce waste. They ensure that virtually all the fuel used by your furnace turns into adequate heat for your home.
What Do Furnace Efficiencies Mean?
The efficiency of furnaces on the market is measured by the Annual Fuel Utilization Efficiency (AFUE). An AFUE efficiency rating is used for furnaces that burn gas, oil, or propane fossil fuel sources. On the other hand, heat pumps have their efficiency measured by the Heating Seasonal Performance Factor (HSPF). We will come back to heat pumps at the end of this article.
For natural gas, oil, or propane furnaces, an AFUE rating essentially measures a furnace's ability and efficiency in converting fuel to energy. For example, an older furnace with an 80 percent AFUE rating can turn 80 percent of the energy it consumes into usable heat for a home. The other 20 percent is used and wasted during the heating process. Obviously, the higher the AFUE rating for your furnace, the more energy-efficient your home will be. Despite the advances and improvements in furnace efficiencies, a standard-efficiency furnace is still considered one that achieves only an 80 percent AFUE rating. In most homes across the country, around 20 percent of the fossil fuels used for heating are essentially lost as waste exhaust.
How Do I Know What Size Furnace I Need?
Opting for a higher furnace efficiency is undoubtedly one way to lower your heating costs and the energy demand for keeping your home at a comfortable temperature during the winter. However, improperly sizing your furnace can also lead to wasted energy. HVAC professionals calculate the optimum furnace size through a mixture of three different calculations:
Design Load
Design load includes fixed details of the home, such as:
- Square footage
- Average winter temperatures
- Insulation levels or capacity
- The tightness of the building envelope, and
- The orientation of the house to the sun for passive heating benefits
Extreme Load
The extreme load takes the possibility of severe winter cold events into consideration.
Part Load Condition
This measurement considers the cycling on and off of the furnace, which occurs when the actual heating load falls beneath the design load. Consistent cycling on and off reduces the lifespan of your furnace. It can also reduce the energy efficiency of your heating system and hinder humidity control in your home.
Heat Loss/Heat Gain
A heat loss or heat gain calculation is also necessary to determine your home's best furnace. This calculation determines how much heat escapes from your home in a certain amount of time. It more accurately calculates the best-sized HVAC equipment for a given family.
For homeowners wanting to get a basic idea of the proper size for a furnace, you need to know the square footage of your home and which of the five climate zones your home is within. Each climate zone has a recommended heating factor: the number of BTUs needed per square foot of your home.
- Zone 1: 30 to 35 BTUs (Miami and Houston, for example)
- Zone 2: 35 to 40 BTUs (Coastal California and Atlanta, for example)
- Zone 3: 40 to 45 BTUs (Virginia and Kansas, for example)
- Zone 4: 45 to 50 BTUs (Boston and Chicago, for example)
- Zone 5: 50 to 60 BTUs (Buffalo and Minneapolis, for example)
To calculate an approximate size for a new, energy-efficient furnace, multiply your home's square footage by the recommended heating factor. For example, a 2,200 square foot home in Chicago would need a furnace with a BTU rating between 99,000 and 110,000. Of course, many other factors (including insulation, orientation, etc.) will affect this rating. However, this will give you a baseline for comparing different furnace options on the market. For in-depth guidance on how to calculate your home's heat loss and heat gain, check out our Rise Guide.
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Wood Furnaces
Wood furnaces provide powerful, efficient heating for your entire home, offering an economical and sustainable solution for large spaces.
What Questions Should I Ask A Furnace Installer?
To make sure that your contractor is doing everything they can to size your furnace correctly, you can ask the following questions:
- How did you calculate the proper size for the furnace you recommend?
- Did you make a heat loss/heat gain calculation for the home?
- What factors were included in this heat load calculation?
- Can you provide me a copy of the heat loss/heat gain calculations?
- If your home has an alternative or secondary source of heat (such as a wood stove), you might also ask if this factor was taken into account.
- What is the AFUE for the furnace?
- What is the expected lifespan for the furnace?
Rise Writer
Expert. Practical. Sustainable.
Article by
Tobias Roberts
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.
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