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7 Key Considerations When Sizing a Furnace for a House

Published October 20, 2023
7 Key Considerations When Sizing a Furnace for a House

Do you need help choosing a furnace for your home? Call the experts at Top Flight Heating & Air at 302-329-8003.

Milton’s furnace installation experts know that sizing a furnace for a house takes careful consideration. Properly sizing a furnace for a house ensures your and your family’s comfort no matter how cold it gets outside. A furnace that is too small can lead to cold indoor temperatures, while one that is too large can quickly send the heating bill skyrocketing.

Our HVAC experts explain seven tips to help you choose a furnace that is the right size for your home

 The House’s Square Footage

One of the first considerations to make when sizing a furnace for a house is the square footage. Larger homes need furnaces with a higher heating output. British Thermal Units (BTUs) are the standard method of measuring heat energy and the general standard when heating a home is 30 to 60 BTUs for each square foot of space in the house, but this varies depending on the climate where you live.

To choose a furnace with the necessary power to heat your home, first determine the total number of square feet in your home, then consider the amount of BTUs needed for that size home.

These are some of the furnace BTUs that are standard based on the home’s size:

  • 35,000 – 75,000 BTUs for a 1,200-square-foot house
  • 55,000 – 110,000 BTUs for a 1,800-square-foot house
  • 65,000 – 125,000 BTUs for a 2,100-square-foot house
  • 70,000 – 145,000 BTUs for a 2,400-square-foot house

Although considering the square footage when selecting a furnace is an important measure, it’s not the only heating factor to keep in mind. You will also want to consider the level of furnace efficiency as well as the climate in your area to find out how many BTUs your furnace needs to adequately heat the home.

The Climate in Your Region

The climate in the area that you live in will affect how many BTUs per square foot your furnace needs. Colder climate zones call for a furnace with more heating power, while more temperate climates call for less heating efficiency. The first step is to determine your climate zone. Then, you can see how many BTUs HVAC experts recommend based on your climate zone.

This list will help you choose the correct BTU output per square foot for the furnace you need:

  • Zone 1: Desert and Southern areas: Areas like Texas, Florida, and subtropical areas require 30 to 35 BTUs.
  • Zone 2: Mediterranean areas, including California and Sunbelt areas, require 30 to 35 BTUs.
  • Zone 3: Humid Continental and Oceanic areas, including Virginia and Missouri, require 40 to 45 BTUs.
  • Zone 4: Midwest and Northern New Mexico areas, including New York, Boston, and Chicago, require 45 to 50 BTUs.
  • Zone 5: Northernmost states, including Minnesota’s Twin Cities, call for 50 to 60 BTUs.

To figure out the right level of output, you can multiply your home’s square footage by the BTUs required for your climate zone.

The Furnace’s Heating Capacity

Considering the heating capacity of the furnace is key when determining which size furnace you need. The heating capacity refers to how much heat the furnace puts out per hour in BTUs.

The higher the BTU output, the warmer the furnace will be able to heat the home. The lower the rating, the lower the furnace’s heating capacity.

The Furnace’s Efficiency

Knowing the efficiency rating of the furnace you are considering is one of the critical factors when sizing a furnace for a house. The efficiency rating percentage describes how well the furnace can create a heated air output. Furnaces generally come with at least an 80% efficiency rating. However, the more powerful models have a furnace efficiency rating of 90% to 95%.

Your Home’s Insulation

The level of insulation in your home directly impacts the furnace’s ability to heat your space. If the home has insufficient insulation in the walls or attic, this results in inefficient heating and wasted money. You’ll have to run your furnace for longer, only to lose heat through the attic and walls.

Before purchasing a furnace, it’s helpful to have a professional check your home’s insulation to see if you need more insulation.

Windows in the Home

Checking the size, type, and number of windows in the home before furnace installation is important when sizing a furnace for a house. Double-pane windows efficiently keep the heated air in the home for a longer time. However, smaller windows tend to be more energy efficient than larger ones.

The number of windows in the home can also affect the furnace’s efficiency. A home with many windows will require a furnace with more BTUs, while homes with fewer windows can handle furnaces with fewer BTUs.

Multi-level homes

Homes that have several floors will have varying heating needs than one-level homes. When selecting a furnace, it’s helpful to consider how many floors the home has and the square footage on each floor.

Consult with an HVAC Expert

Taking each heating factor into account will go a long way toward helping you choose the best furnace to fit your home. Before purchasing your new furnace, you will want to consult with an HVAC expert from Top Flight Heating & Air.

Before your furnace installation, one of our heating professionals will provide a consultation to determine which furnace is the right fit for your home. In addition to these seven factors, we also consider ceiling height, age, and the home’s construction.

The level of weatherization that a home has undergone will also affect the ability of the furnace to heat the space. Once we have considered all of the variables, we can recommend the furnace that will heat your home sufficiently.

Top Flight Heating & Air is here for all of your HVAC needs! Call our HVAC experts at 302-329-8003! for help sizing a furnace for a house and for quality furnace installation.

About The Author

Ryan Brower

Ryan Bower is the owner of Top Flight HVAC in Milton, Deleware. He is an expert HVAC techician and writes about his life on the job and HVAC projects that he has encountered throughout his career.
Keith Banks
Keith Banks
1726104506
I recently had the pleasure of working with Ryan and the team of Top Flight Heating & Air, and couldn't be more impressed. From start to finish, their team demonstrated professionalism, expertise, and genuine commitment to customer satisfaction. Highly recommend.Keith
Ann Marie Morris
Ann Marie Morris
1725392203
They were on- time, explained what they were doing & did a great job. Would definitely recommend them. Excellent Service!!
Bryson Ezell
Bryson Ezell
1725041346
Great customer service from first phone call to payment. Thank you Isaiah!
Tara Rumer
Tara Rumer
1724960759
We have had all amazing experiences with Top Flight Heating and Air. Nothing but good to say about them. They are always quick to come out and handle our issues quickly every time.
george donahue
george donahue
1724860439
Absolutely top notch. Technician found problem, explained what had to be done in detail. Exceptionally polite and courteous. If your looking for down to earth people, this is the place. No hassle whatsoever.
Earl Dunnock
Earl Dunnock
1724850667
Arrived on time, very thorough!
ROBERT BANKS
ROBERT BANKS
1724850591
Theresa Roche
Theresa Roche
1724543015
Great service with friendly, professional service providers
P West
P West
1724444878
Tyler and Joseph came by today to do some follow-up work. They were on schedule and on time. They did a great job and I very much appreciate the work they did. Now my house is ready for encapsulation. Once the encapsulation is complete, and with my new AC/Heat system, both will add some great value and comfort to my home. Thanks TFH&A!
Betty Ann Dawson
Betty Ann Dawson
1724358933
The guys were great!
noland Hazzard
noland Hazzard
1724336529
Wendy Carmean
Wendy Carmean
1724273762
This was my first time using Top Flight Heating & Air service and I will say they are wonderful! I called to schedule and they were able to schedule me quickly. I received a courtesy text when the technician was on his way which was very convenient. The technician Isaiah, was very professional and knowledgeable! He not only diagnosed my issue, but also fixed my issue. Thank you Isaiah for making this experience a pleasant one!!
larry ell
larry ell
1724257829
Top Flight Heating and Air did quality work for us, and we now use them for twice a year Maintenance Plan. They have great techs in our experience. Ryan runs a tight ship and is hands on w customers. Recommended
Michael Weal
Michael Weal
1724245967
Great to deal with. Easy to set up appointments. Always on time and they know what they are doing. I had them replace my entire HVAC system and all of the maintenance check ups.
T D
T D
1724170836
Very quick from estimate to install for our complete heat pump replacement. Follow up complimentary service has been easy to schedule.
Donald Dukes
Donald Dukes
1723931957
Prompt and knowledgeable
Tom Farinelli
Tom Farinelli
1723915726
Tech showed up on time and explained what he would do and at the reviewed his findings with me.
Dave Francis
Dave Francis
1723910488
Top Flight installed a new Heat Pump/AC system at my home quickly and efficiently. Everything works the way it should.
John Gulick
John Gulick
1723909426
I moved from a disappointing service company to Top Flight 4 months ago and they operate like a service company should, office staff attentive, scheduling easy, so far no cancellations, service techs good.
John Swidrak
John Swidrak
1723656768
It was refreshing to find a local business that is both professional and customer service focused. Staff are very personable and get the job done quickly. No hard up-sell tricks during the service call... something that seems to be the norm with many other companies who force their service personel to try to generate extra income. We were impressed enough to switch all of our HVAC service contracts to Top Flight.
M M
M M
1723645362
Ryan was very helpful and explained the problem to us. He was very polite and answered our questions.
p “Patricia” weath1
p “Patricia” weath1
1723644657
Isaiah Barnes was Professional, Knowledgeable & Kind. Joe, Isaiah's assistant is also of great character. I trust both of these folks completely. So grateful to have found Top Flight. They will continue to have my business as long as I am in the area.
Robert Herman
Robert Herman
1723643458
Shout out to Top Flight Heating and Air conditioning. Sunday we had no air conditioning and by Tuesday morning we were up and running. Michael and Ryan were very professional and on time. Love the quick response and communication with us, text and emails.Supporting Local! Would highly recommend.
james shockley
james shockley
1723641357
Top notch very cordial very politeIsaiah was great
Laura beasley
Laura beasley
1723556387
Courteous office staff helped get a tech out to our home as quick as possible. Tech was knowledgeable, friendly and efficient. Have already referred them to two of our friends for service!
Kathy Board
Kathy Board
1723552756
We love the Split unit. Customer service is very good.
Edris Kalibala
Edris Kalibala
1723485558
Roger Berwanger
Roger Berwanger
1723230745
AWESOME REPAIR JOB BY Michael. We signed up for the annual maintenance plan too.
Erin Misasi
Erin Misasi
1723124347
The crew came out, assessed the problem and corrected it within minutes. They were kind and professional. Highly recommend.
Diana Erney
Diana Erney
1723041243
Top Flight has well trained technicians that care about you as a customer, listen to your concerns and try their best to solve the problem. We have to give special kudos to Isaiah because he is so conscientious, respectful, and proud of the work he does!
Karl Haller
Karl Haller
1723038259
Ryan did great job in explaining job to be done, and Isiah did great job on installation.
Steve Koehler
Steve Koehler
1723037951
We had an issue that I believe was created by our previous service company, name starting with H. In that Top Flight had recently did a heater check up, they came to my home on a Sunday (when we were away) fixed the issue and did not charge us!!! Their actions saved our home from freezing pipes and that's why I'd give them 10 stars if I could.
Paul Santomauro
Paul Santomauro
1723036318
Cape Flooring
Cape Flooring
1722867418
Top Flight not only provides quality work, they communicate promptly, provide outstanding customer assistance, and consistently meet the expectations they set. We couldn't recommend them more and it feels great to support a locally owned community business.
beth bittner
beth bittner
1722759803
IM JUST ME
IM JUST ME
1722569205
Reliable, affordable, and on point! Had issues with my air conditioning for years, after spending thousands with multiple other companies, I found Top Flight! One visit and everything was working perfectly! The only company I'll trust with my heating and A/C needs! Highly recommended!Thank you for superb service!Michelle Phillips
Ron Marra
Ron Marra
1722539276
This company is great and has great reviews i haven't had any problems with them however 1 very big tip do not deal with these company's that have no reviews because they have so many bad reviews that they won't list any at all i got ripped off twice by these company's that come in an hour and so on, so i stuck with this company and very satisfied.
J Indrisano
J Indrisano
1722535712
I am so pleased to have chosen Top Flight Heating and Air to service my HVAC system. They are easy to schedule; communicate frequently the day of the visit and provide superior service!
Betty Lowman
Betty Lowman
1722532823
Isaiah was great!Professional and answered all of my questions. He explained how things worked, advising me of the condition of my equipment and took photos of the unit and conditions found then explained everything. I would certainly recommend this company and Isaiah without any hesitation...
Glenn Williams
Glenn Williams
1722529588
Excellent service
Chris Derchin
Chris Derchin
1722471412
First service by Isaiah was outstanding, he took time to explain what he was going to service before & after he was finished. I was promptly contacted next day by Christian to set up follow up Appt. Now I understand why they have 5 stars on the Google reviews.
Don Disharoon
Don Disharoon
1722454064
Hopefully the problem can be resolved asap! Very good explanation of the problem and very professional!
grk
grk
1722444171
Responsive, professional, knowledgeable
Adam Kindl
Adam Kindl
1722380126
Great experience. Ryan and his staff are very professional. I love the fact that they offer monthly payments instead of one lump sum per year. Their newsletters are great. The receptionist's professionalism is second to none. Everyone that I have talked to and dealt with is extremely knowledgable.
Karin Adkins
Karin Adkins
1722265569
Thanks for quick response to our need to replace a flooded condensate pump! Appreciate Isaiah’s ‘can do’ attitude …you guys are great!👍🏻
HydroZen Waterscapes
HydroZen Waterscapes
1722196971
Top Flight will be our go to for all things HVAC moving forward. We have tried several local companies and only Top Flight delivered as promised. We will always recommend them any can not say enough good things about them.
Brian Shannon
Brian Shannon
1722097539
Sheri Deeb
Sheri Deeb
1722091506
Tiffany Clark
Tiffany Clark
1721954565
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