Welcome to the second blog in our three-part blog series about buying a new San Diego heating system . Our first blog introduced seven types of heating systems and fuel sources. In this blog we’ll cover the different sizes and efficiency.
Your Heating System: Choosing the Right Size & Efficiency
In general, big homes need big furnaces and small homes need small furnaces. Sizes are rated in British Thermal Units (BTUs) and BTUs are listed in thousands. For example, a mid-sized gas furnace would be 70,000 BTU. Since an exact BTU size isn’t available or really even necessary sizes (they move up in about 20,000 BTU increments), you would select the size that is closest to your needs. Furnace labels often show furnace “input” BTU ratings and “output” BTU. “Output” means how much heat the furnace will actually put into the home, and is the BTU listing you will use to select your new home furnace.
How do you know what size furnace is right for you?
1) Manual J Load Calculation
This is a scientific approach and will be the most accurate. This approach requires that you gather information about your home’s construction materials, insulation levels, room sizes, etc. to make a calculation to determine the appropriate heating and cooling requirements needed. Online software  can be purchased to use this method, but it will take several hours to calculate.
2) Heating System Sizing Estimator
You can use this online tool  to get a quick, rough estimate. It won’t be exact, but when used in connection with other information it can provide a fairly close approximation. You should still consult an HVAC contractor before finalizing your decision.
3) Neighborhood Comparison
Compare your home to similar homes in your area. If a neighbor has the same size home, with a properly sized furnace, then the same size may work for you.
4) Ask a Contractor
Most furnace professionals give free in-home estimates for installing new heating equipment during which they will recommend a unit size. A San Diego heating specialist  familiar with the homes in your area will be able to give you an idea of what size you need and confirm that with a heat load calculation.
5) Replacing with the Same Size Heating System
If you are replacing an existing furnace, look at what size you already have. If it is the correct size for your home, replace it with the same size. To determine what size you currently have, look at the nameplate on the furnace (usually located somewhere inside the unit). Remove the service panel to find this. IMPORTANT: MAKE SURE TO REPLACE THE SERVICE PANEL SECURELY. Make note of the “output” BTUs. Newer furnaces are higher efficiency and for every input BTU, you get more output BTUs (heat) in your home. So a new furnace will be smaller (lower input BTU rating) than your existing furnace.
Simply replacing your heating system with the same size works best if you have lived in the home long enough to go through a winter and determine that it is operating properly. If you’ve added insulation or upgraded your windows, you may need a smaller furnace.
The sizing process might involve a bit of educated guesswork, but depending on the type of furnace you’re shopping for, there are only a few sizes to choose from which move in 20,000 BTU increments. So the odds that you’ll get the right size furnace are very good. If you are looking for a gas or propane forced-air furnace, you might want to select what’s called a two-stage furnace. A two-stage furnace is actually two furnace sizes combined into one unit so using one of these furnaces means it covers a wider spread of sizing capabilities.
Next, you’ll choose how energy efficient you would like your furnace to be. This is personal, based on how much you want to save on your heating bill.
Gas, oil or propane heaters have different energy ratings. These are indicated as an Annual Fuel Utilization Efficiency percentage (AFUE). For electric heat pumps, the rating is a Heating Season Performance Factor or HSPF number. The higher the AFUE or HSPF rating, the more efficient the heating system is. Higher efficiency heaters will produce the same amount of heat as lower efficiency heaters with the same BTU output, but the higher efficiency heater will use less fuel doing so. Fuel savings almost always means money savings.
Older heating systems with lower efficiencies cost a lot more money to operate, compared to newer systems. Furnaces that are 20+ years old are around 65-70% efficient and old heat pumps are a 5-6 HSPF rating. New forced air furnaces or boilers are between 80-95% efficient. If you buy a heater that is 95+% efficient, the Federal government may even give you a rebate around $150-200.
Investing in a highly efficient  heater is a great idea if you live in San Diego County, plan to stay in your home four 4+ years, like to save money and want to be kind to the environment.
Selecting Your San Diego Heating System: Next Step
We’ve covered the different types of furnaces and heaters available, how to determine what size you need for your space and efficiency ratings. Later this week, in Part 3, we’ll take a look at heating comfort features and brands. Subscribe to our blog or come back later this week for more on these additional considerations.