AC And Furnace: The Complete Beginner’s Guide !

In this blog post, we will know in detail AC and its integration with furnace and the furnace size.

What Is AC?

AC stands for air conditioning and it is a part of the HVAC system that acts as a refrigerant and is installed at homes to give a cooling effect.

AC And Furnace

What Is a Furnace?

The furnace is a heating system that uses fans and coils and distributes hot air throughout using ducts.

AC and Furnace

AC and furnaces are together called HVAC systems and are responsible to produce cooling and heating effects to your homes.

AC uses vents and furnaces use ducts to circulate air throughout the building and both are tied as a single component with individual operation.

How To Calculate Furnace Size?

When heating your home, size matters. Too small and it won’t heat efficiently, if it is too big and you’ll waste energy and money. 

To find the right fit, there’s a heating BTU calculator you can use to calculate BTUs based on,

  • Square footage
  • Climate zone
  • Insulation
  • Window area
  • Sun exposure
  • Ceiling height
  • Layout

The heating BTU Calculator uses the below formula to calculate the BTUs needed to heat the component,  

(Desired temperature change) x (Cubic feet of space) x . 133 = BTUs needed/hour

Some contractors use a rule of thumb based only on square footage, but for accurate sizing, consult local HVAC pros who can assess all relevant factors.

Calculation of Furnace Size

When heating our homes, furnace size is vital. Furnaces come in a variety of sizes and efficiencies.

(Desired temperature change) x (Cubic/square feet of space) x . 133 = BTUs needed/hour

Let’s break it down with actual data in a table.

Square footageHeating BTU Calculator
100 to 1505,000
150 to 2506,000
250 to 3007,000

BTU Input and Output

These details, plus climate zone heating factor, give an estimate of British Thermal Units (BTUs) needed to keep the home warm in winter.

Accurately determining the size of a furnace for one’s home requires considering BTU Input and Output

This takes into account factors such as square footage, climate zone, insulation quality, windows, sun exposure, ceiling height and heating needs.

However, this calculator is just a guide. Professional advice from an HVAC contractor is needed for an accurate recommendation.

Gas furnaces have an Annual Fuel Utilization Efficiency (AFUE) rating of 90%. Heat pumps are even more efficient, but may not work as well in cold climates.

Two houses with the same design, built in different years, will perform differently due to wear and tear over time. 

Factors Affecting Furnace Size

When picking the right furnace size for your home, there are many elements to consider. Here are some key ones to keep in mind.

  • Square footage is a major factor. For instance, a 2,500 sq ft house needs a different-sized furnace than a 1,500 sq ft one.
  • Size of home
  • Location of home
  • Insulation of building
  • Energy efficiency rating 

Ductwork layout efficiency, leaks, and other factors should also be looked at.

Experts like HVAC contractors have software models and production tables to help assess your particular situation.

By considering all these, you can have an efficient furnace that leads to lower energy bills. Use our BTU calculator and local HVAC pros for easy furnace size selection.

How To Choose the Right Furnace Size?

Similar-sized houses can vary in furnace size due to variables like insulation quality, room layout and uneven heating. 

An HVAC contractor can give a more exact estimate by considering variables like sun exposure, ceiling height and windows

Use an online heating BTU calculator to get estimates for how many BTUs you’ll need based on system efficiency rating and output capacity.

Finding the ideal size for your furnace can be tricky. It needs to factor in the square footage of your house, climate, heating requirements and more

Here’s what to note:

Size of Home (sq ft)Furnace Size Needed (BTU)

Hiring an HVAC Contractor To Install Furnace

Finding the right HVAC contractor? Here are a few things to keep in mind.

  1. First, consider the size of your house.
  2. Look at things like square footage, climate zone, insulation quality, and sun exposure. They all impact heating and cooling.
  3. For an accurate estimate of how many BTUs you’ll need, use a calculator or consult a pro.
  4. Look at energy efficiency ratings (AFUE) and available rebates/discounts.
  5. Reach out to local HVAC pros for recommendations and estimates.
  6. Don’t commit until you compare costs and energy bills!


Analyzing factors such as furnace and square footage is important for efficient heating in a house. A furnace sizing calculator can help, taking into account square footage, insulation quality, and climate zone. Experts suggest considering ceiling height, sun exposure, and windows and duct leaks too.