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Heat Pump & Furnace Systems

Easy System Selector Tool

Use this tool to guide you to the best heating and cooling solution for your home.

Step 3: Heat Pump & Furnace - BTU, Tonnage and Orientation

Upflow

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Upflow Furnace

Takes in air from the bottom and pushes warm air upward (common in basements). Most commonly used with floor vents.

Downflow

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Downflow Furnace

Pulls air from the top and pushes warm air downward (often used in attics). Most commonly used with ceiling vents.

Horizontal

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Horizontal Furnace

Moves air side to side, usually installed in crawl spaces or tight areas. Usually used sidewall or rooftop venting.

What orientation is your furnace?

How many BTUs for your furnace
do you need?

How To Calculate BTU

How to Calculate BTU

BTU (British Thermal Unit) measures the amount of heat an HVAC system can add or remove per hour. It is used for various HVAC systems and it can be calculated from tonnage as:

  • BTU = Tonnage x 12,000

If you don’t know your system’s tonnage, you can usually find BTU listed on your furnace’s model number on the data sticker, usually inside the cabinet door or on the inner/outer wall of the cabinet.

Look for M/N, Prod, Mod No, or Model Number to search for a replacement. If needed, the data sticker also usually includes the year the unit was made, voltage, and serial number.

To find BTU/hr, check the input/output labels and calculate efficiency by dividing output by input.

Example (left): The input is listed as 70,000 BTU/hr and the output is 57,000. If you divide 70,000 / 57,000, you will find that your furnace is 81% efficient.

What tonnage do you need for
your heat pump?

How To Calculate Tonnage

How to Calculate Tonnage

Tonnage applies to the following systems:

  • Air Conditioners (AC): Measures cooling capacity
  • Heat Pumps: Measures both heating and cooling capacity
  • Air Handlers: Do not have tonnage themselves, but must be matched to tonnage of AC or heat pump

There are two ways to calculate tonnage:

  • From BTU rating:
    Tonnage = BTU Rating / 12,000 (Because 1 Ton is equivalent to 12,000 BTU)
  • Using Square Footage (Estimate):
    Tonnage = (Square Footage x 20) / 12,000 (A number from 20 to 25 is used for BTU per sq. ft. depending on insulation, climate, and efficiency)

Example (left): You can also check the model number included on the data label on your current system. Many manufacturers encode BTU ratings in it. Look for a 2-digit even number within it (e.g., ACIQ-24-HP = 24,000 BTUs = 2 tons).

TIPS

Furnace Orientation

Furnace orientation matters because it determines how air moves through the system, ensuring proper performance, efficiency, and compatibility with your home’s ductwork.

Using the wrong orientation can cause poor airflow, inefficiency, or require costly duct modifications.

 

Tonnage & BTU

Tonnage in heat pumps refers to the unit's heating or cooling capacity, where 1 ton equals the ability to remove 12,000 BTUs of heat per hour.

BTUs in furnaces measure the heating capacity, indicating how much heat the unit can produce per hour.

How to Determine the Right BTU or Tonnage for Your HVAC System

Use the guide and tools below to find the right system size for your space.

Step 1: Locate Your Current System’s Info

You can usually find the BTU listed on your furnace’s data sticker, often located inside the cabinet door or on the inner or outer wall of the cabinet. On an air conditioner, the data sticker is typically found on the outer panel of the outdoor condenser unit, often near the electrical disconnect box.

Look for terms like M/N, Prod, Mod No, or Model Number to identify your system. These numbers can also help you find a replacement if needed and the product manual (if you need to look up the BTU/Tonnage).

Step 2: Calculating BTU and Tonnage

You can also use the model number to determine BTUs. You’ll find an even number within the model number string. Multiply this number by 10,000 to calculate the unit’s BTU.

From there, tonnage is typically calculated by dividing BTUs by 12,000 (since 1 ton = 12,000 BTUs).

If you don’t have product data available, you can also use our sizing calculator to use square feet to determine your needs.

Furnace Data Sticker

Model Number: DGAT070BDF
BTU: 70,000

AC (Heat Pump) Data Sticker

Model Number: ACIQ-24-HP
BTU: 24,000    TONNAGE: 2.0

Sizing Calculator