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Can a Furnace Unit be Oversized?

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Can a Furnace Unit be Oversized?

Posted On: March 18, 2025

Can a Furnace Unit be Oversized?

a furnace can absolutely be oversized, and it’s a more common problem than you might think. While it may sound like having a more powerful furnace is a good thing, an oversized unit can actually cause several problems for your home’s comfort and efficiency.


Signs Your Furnace Might Be Oversized

  1. Short Cycling — The furnace turns on and off frequently because it heats the space too quickly, shutting off before completing a full heating cycle. This leads to uneven temperatures and increased wear on the unit.


  2. Uneven Heating — Some rooms may feel too warm, while others stay cold because the heat doesn’t distribute evenly before the system shuts off.


  3. High Energy Bills — Short cycling uses more energy since the furnace draws the most power during startup. Constantly restarting increases your energy costs.


  4. Excessive Wear and Tear — The repeated on/off cycling causes parts to wear out faster, leading to more frequent repairs and a shorter lifespan for the unit.


  5. Poor Humidity Control — Furnaces also help control humidity levels in your home. An oversized unit doesn’t run long enough to properly remove moisture from the air, leaving you with a clammy, uncomfortable environment.



What Causes an Oversized Furnace Installation?

  • Improper Load Calculation — If the HVAC contractor didn’t properly calculate your home’s heating load (taking into account square footage, insulation, windows, etc.), they may have installed a larger furnace than necessary.
  • "Bigger is Better" Mentality — Some people assume a larger furnace will heat the home faster, but this actually leads to inefficiency and discomfort.
  • Old House Upgrades — If you’ve added insulation, replaced windows, or improved energy efficiency, your original furnace may now be oversized for your current needs.

How to Fix an Oversized Furnace

  • Replacement — The most effective fix is replacing the unit with one properly sized for your home. An HVAC professional can perform a Manual J Load Calculation to determine the right size.
  • Adjustments — In some cases, technicians can modify the blower speed or adjust gas pressure to reduce output, but this is more of a temporary fix.
  • Zoning Systems — If replacement isn’t an option, installing a zoning system can help direct heat to specific areas more effectively.


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See What Our Customers Are Saying:

by Donna J, in Ajax on Twintech Heating and Cooling

Twin Tech was great; they were honest, reliable and very thorough. I would recommend their services and will definitely be using them in the future.

by Sheila C. Pickering on Twintech Heating and Cooling

Hi Dave, Thank You Dave for coming to my aid this past summer when my AC quit. Your men did a great job installing and cleaning the area. The unit is working very well and i would highly recommend your company TwinTech. Dave you delivered what you sold and i truly appreciate it.

by Darin O. Whitby on Twintech Heating and Cooling

My experience with TWINTECH has been excellent, start to finish. While doing market research I made a list of several local companies and called them for some high-level information. Dave was the first to call me back, and the only one to book a meeting to see my place in order to give an informed, accurate estimate. He reviewed the different AC makes and models with me, explained the technology, and made a recommendation appropriate to my home. The installation went smoothly. I had one post-installation issue – there was moderate noise/vibrations coming from the duct system. I called about this, booked an appointment, and the technician resolved the issue during the service call. I feel assured having a 10-year warranty on parts & labour. I would recommend TWINTECH to anyone considering an AC or furnace for their home. Regards,

by Bill P. Whitby on Twintech Heating and Cooling

Thank you for your attention to detail regarding my purchase of a new air conditioner. Twintech arrived at the appointed time and were totally professional on the installation process completing the job quickly. PS thanks for the assistance applying for the government rebate

by Sam C, Pickering on Twintech Heating and Cooling

Dave and the guys from Twintech did a great job of installing my AC. They came on time did a nice neat job and cleaned up after themselves! Do not waste your time call Twintech first.

by Mary W, Whitby on Twintech Heating and Cooling

My AC unit was not working at all and our furnace that was still working but not giving us any trouble was over 15 years old. So I had 3 heating companies come out to give us a quote on replacing both the AC and the furnace at the same time. Two companies right away recommended that I replace both units simply because they were old. Dave from twintech however suggested that we save some money and replace the AC only because it seemed to him that the furnace was still in great shape and was running fine. He told us that he would have his technicians inspect the furnace thoroughly when they had it apart to install the AC. My husband was at home when the furnace was apart and was very impressed when the tech took him downstairs to personally show him that the furnace was in excellent working condition. He also cleaned the furnace at no extra charge. So now I have an honest heating and AC company that I can highly recommend to other home owners. Great job Thank You!

by Scott B, Whitby on Twintech Heating and Cooling

I had made the decision to replace my furnace and AC earlier this year. After meeting with several HVAC contractors I decided to go with Dave and his company. Dave was on time, polite, friendly and very professional. He took the time to answer all my questions and to explain the scope of work that would be required to do the job. The technicians arrived on time did a professional installation and completed the job on schedule. They respected my home by putting down vinyl runners to protect my floors and did a very thorough clean up. I’m very pleased with my decision to go with Dave and his team. I would highly recommend them to anyone who is considering upgrading their furnace and air conditioner.

by Mel F, Oshawa on Twintech Heating and Cooling

I have no problem in recommending Dave and the TWINTECH team to any home owner who is looking for quality heating and AC products and expert service.

by Eric Y, Greenbank on Twintech Heating and Cooling

Dave was great in helping me get the proper units for my property, as well as getting them installed. The installers arrived when they said they would, and completed the project on time, and professionally. If I needed another furnace, I would use Dave again.

by Ed B., Whitby on Twintech Heating and Cooling

I have known Greg and Grant Dainty for many years and have used their company for my house and business. I recommended them also for my parents and sister and they all have been very satisfied with the quality of work for a reasonable price. I just recently had them install a new HVAC system in an older house and was very pleased with their work. Craig in Pickering. After meeting with various heating and air conditioning contractors I was referred to Twin Tech Heating and Cooling through a family member. Greg and Grant arrived at my home and provided me with an estimate and a plan as to how they were going to remove and replace my furnace and air conditioner. On the day of install Greg and Grant arrived at my home on time and were very professional and extremely courteous as to any questions or concerns that I had. The removal and install was truly professional and the attention to detail was exactly what I was looking for. I’ve seen many installs from other contractors and I couldn’t be any happier to have had such a clean looking install. The sheet metal work, ducting and venting all look fantastic. Upon completion Greg and Grant left me feeling extremely happy and very fortunate of a job well done. Thanks again Twin Tech!!

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See What Our Customers Are Saying:

by Robert Rogers on Twintech Heating and Cooling

Very pleased with the professional service that TwinTech Heating and Cooling provided in replacing my furnace. I got several quotes from different service providers. Their price was excellent and they explained the features very well. We are very glad we went with TwinTech and highly recommend their services.

by Robert Mizuno on Twintech Heating and Cooling

We were new homeowners in need of a second opinion. TwinTech Heating & Cooling were Amazing and professional. Very knowledgeable and great service all around. Recommend to anyone looking for honest and reliable services. Treated with respect and care. Thank you Greg, Mitch and Bob!

by Ruth on Twintech Heating and Cooling

TwinTech is an excellent and honest company! I called them for a second opinion after being told by another company that I needed to replace my furnace. Turns out this was not the case at all! I did not need a new furnace. TwinTech did not push to make an unnecessary sale and saved me from a huge expense. Bob and Mitch were extremely professional and above all honest! I definitely recommend TwinTech!

by Anna Chin on Twintech Heating and Cooling

Amazing experience with TwinTech Heating & Cooling! Their team was professional, knowledgeable, and efficient from start to finish. They installed my new furnace quickly and left everything spotless. The technicians took the time to explain everything and made sure I was comfortable with the system before they left. Great customer service and fair pricing. I highly recommend them for anyone needing HVAC services!

by Connor Agnew on Twintech Heating and Cooling

Great experience all around. Bob was sharp and easy to talk to, and Greg handled the installation perfectly. Would hire them again in a heartbeat.

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