Furnace Sizing: How Big of a Furnace Do I Need?

When choosing a new furnace for your home, you will run into a diverse range of sizes and furnace types. Size matters when picking an efficient furnace. Furnace sizing will make or break your comfort (and your wallet) during use. 

But how can you determine what furnace size your home needs? The math involved can make it seem more complicated than it is. You need only a simple formula to select the right size furnace. Denville’s reliable HVAC services provider offers the following guide for your edification. Call us at (973) 490-4881 if you have further questions. 

The Basics of Furnace Sizing

Furnace output is measured in British Thermal Units (BTUs). A BTU signifies how much energy your furnace needs to heat one pound of water by one degree. An incorrectly sized furnace will use more BTUs to heat your house, ultimately driving up your power bill. 

An oversized furnace will constantly short cycle by blasting hot air. Your thermometer will pick up the rapid temperature increase and signal the furnace to turn off. As a result, your house won’t get the even circulation you need to sustain your desired temperature. 

When a furnace is too small for your house, it struggles to bring the temperature up. Your power bills increase even though you can’t stay warm. The constant cycling also causes wear and tear on the furnace mechanics, leading to more repairs. 

The Size of Your Home

Your house’s square footage is the most important determining factor in calculating furnace size. You can find your square footage on the house’s blueprints or pertinent property documents. If you can’t access these documents, you can count the square feet in your home. 

Each square foot has 12-inch sides. Get a rough estimate by measuring 12-inch squares on the floor of each room. Multiply the total square feet by 200. The calculation gives you an idea of how many BTUs your home requires. 

The Climate of Your Location

Even with a square footage estimate, other things factor into appropriate furnace sizing for your home. Where you live plays an important role in how many BTUs your furnace needs. For example, New Jersey stretches into climate zones 3 and 4.

The southern half of New Jersey is climate zone 3. In zone 3, you need 40-45 BTUs per square foot to keep your house warm. Therefore, you’ll multiply your square footage with a minimum of 40 to get a proper BTU estimate. 

The northern part of New Jersey, or zone 4, requires 45-40 BTUs to efficiently heat a house. So, you’ll multiply by a minimum of 45 instead. If you want to know the highest BTU value, multiply by 50. 

Different states have varying average temperatures during the winter. If you live farther south, the BTUs per square foot will decrease. Often, homes located in the southernmost states don’t need furnaces at all. 

General Calculations

Sometimes, a visual representation can help you understand the arithmetic used for your calculations. Below, you’ll find a few common square footage examples many New Jersey homes have. Use these examples to guide your calculations. 

• For 1000 square feet in zone 3: 45,000 BTU
• For 1000 square feet in zone 4: 50,000 BTU
• For 5000 square feet in zone 3: 225,000 BTU
• For 5000 square feet in zone 4: 250,000 BTU

Other Factors That Determine Furnace Sizing

While these calculations provide more accuracy than square footage, other specifics dictate the type of furnace that will work best with your home. Consider the furnace type, insulation level, and your home’s age when selecting a new furnace. 

If you live in climate zone 3, you should shop for heat pumps. They will efficiently meet your temperature needs with their streamlined technology. Meanwhile, houses located in zone 4 need the power of a furnace to stay warm during bitter winters.

If you want to fit a new house with a furnace, opt for models on the lower end of your recommended BTU range. Older houses usually don’t come with the same energy-efficient fittings and insulation. Therefore, you should seek options with higher BTUs. 

Let Comfort Specialists Help You Find the Perfect Furnace

If you have questions like “How long can a furnace last?” we have all the answers you need! Whether prolonging your current furnace’s longevity or ensuring correct furnace sizing, you can count on Comfort Specialists to keep you informed. Learn more about your furnace options by calling us at (973) 490-4881!