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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 LP from Pickering on Twintech Heating and Cooling

All interactions from sales to installation were Courteous and professional. The installation was seamless and the attention to detail including clean up was outstanding. I highly recommend TwinTech Heating and Cooling.

by David in Pickering on Twintech Heating and Cooling

Twintech's Salesman Dave arrived promptly was friendly and courteous, listened and assured us the installation would be completed according to our requests. The crew arrived early morning on May 11th, 2018 and worked through till late afternoon non-stop. They were very friendly, very professional, their expertise was excellent, their workmanship outstanding and the installation was completed in a timely and efficient manner. We were completely satisfied and happy with the quality of the work.

by Jennifer in Toronto on Twintech Heating and Cooling

I had cold and hot spots all over my 70 yr old home. My furnace is quite new and Greg optimized the fan and furnace. The original installer just took it out of the box with factory settings and installed it- basically running at 50% of capacity. Greg also routed heat into my laundry room, yeah - so now I can renovate laundry room - thanks Greg. He is honest, professional and knowledgeable. I will be calling him back in the spring to optimize my AC as well.

by Happy Homeowner in Toronto on Twintech Heating and Cooling

Wonderful from beginning to end. I tend to fret and worry about home improvements but the excellent team at TwinTech put my mind as ease. They listen, they are patient and best of all ... the work they did is amazing! I chose the Goodman 80K BTU 2 stage furnace and the matching Goodman air conditioner. Greg, Grant and Poitr "Peter" arrived on time, took great care, explained everything to me and they answered all of my questions. They carefully adjusted the factory settings to optimize the furnace for my house and they also checked the duct work in the basement. Dave, the Sales Manager, came by to say "hello" and to see if I was happy. YES, I am happy with the work! The furnace is very quiet. I have it running on low just to circulate the air in the house and it's so much quieter than my old furnace. When I need new duct work for an upcoming basement renovation TwinTech will be my first choice. I highly recommend TwinTech. PS. They were even nice to my dogs.

by Les G. from Pickering on Twintech Heating and Cooling

Greg was prompt on the scheduled day of installation and the work was done well within the time estimated beforehand. Installation was neat and the equipment and scope of work was as specified in the quote. One item I must point out is that we were faced with a "No Heat" situation the day before the scheduled installation and Greg came out to address it free of charge. Not only that, but he also corrected an installation fault with our smart thermostat that was not part of the original job, again free of charge.

by one19 in North york on Twintech Heating and Cooling

Greg came by to do a routine furnace checkup. He was very knowledgeable and professional, letting me know what's being checked/adjusted and giving me tips to ensure everything runs smooth. Very honest and upfront about what's working fine vs. what may need to be fixed/replaced. He didn't attempt to up sell anything that wasn't necessary. I'm glad to have finally found someone I can trust and rely on for all my HVAC needs - furnace, A/C, and hot water tank.

by Paul M. from Toronto on Twintech Heating and Cooling

I'm very happy with the work that was done. Everyone from salesperson to the installers were friendly and professional. They were on time and cleaned up the job site after it was installed. They also answered all my follow up questions promptly. I wouldn't hesitate to work with them or recommend them again.

by Kathy D.in Ajax on Twintech Heating and Cooling

Thanks to the team at Twin Tech for a great job installing my new heat pump/ac unit. The guys were very polite and professional. When they left you would never have known they had been there except for the new Mitsubishi unit on the wall!! would highly recommend the Twin Tech team.

by varga p. in Pickering on Twintech Heating and Cooling

Installed professionally, no delays, no rework needed. Very reliable contractor and sales person. Also installed BBQ gas line and some duct work.

by Private User on Twintech Heating and Cooling

Greg and Grant are friendly, reliable, and knowledgeable HVAC professionals. The twins, Dave and the entire team provided efficient top quality service. Our family plns to use Twintech for all of our future HVAC needs.

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See What Our Customers Are Saying:

by Aaron on Twintech Heating and Cooling

We are very happy to recommend this company to everyone. Our furnace broke down on Sunday morning. We phoned them and before noon Grant the owner showed up. He worked on the furnace for about a hour not wanting to give up to fix the problem. The furnace was 17 years old. I was the one talking about replacing it. End result was the next day it was all done. On the Sunday Bob came over with heaters to warm up the house. We decided to replace the water heater at the same time. Thanks Grant for the excellent work. Thumbs up.

by Linda on Twintech Heating and Cooling

Right on time. Explained how to work the HRV in a different way so the house would not be so dry. Changed my whole house water filter for me as well. Friendly, helpful, caring service!

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!

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