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btuh vs btu per square foot

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I'm new to this forum and not a professional, so please be kind. I'm trying to figure out if my existing gas furnace is sized correctly for my home. I am in Zone 3, where it looks like I should have 45 btu per square foot. My house is 2650 square feet, so I think I need 119,250 btu of heat. My existing furnace is rated at 66,000 btu per hour or btuh. I am not sure how to compare btu with btuh. It seems to me btuh is the rate at which the furnace puts out heat. In other words, a higher btuh rating would heat up my house faster than a lower one. My furnace runs a LOT to keep the house at 68 degrees F when the outside temp is below 30 degrees F. House was built in 2016 so should be reasonably well insulated.

Comments

  • GroundUp
    GroundUp Member Posts: 1,941
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    BTUH is BTU per hour. They are the same thing, and that is how heat sources are sized. 45 BTU per square foot, especially in zone 3, is likely 2-3 times more than is necessary unless the space is poorly insulated. A properly sized furnace will run 24/7 on the coldest day of the year to maintain setpoint- so if it's not falling behind, it's big enough.
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,906
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    There’s no simple btu/ft for sizing. If your furnace keeps your house at temp, you’re properly sized. Likely oversized.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,767
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    The only way to know is to do a heat loss of your house. Many on here used the Slant Fin app which I think is no longer available. There are other calculators I will let others comment.

    You furnace is likely the right size having been installed in 2016. In older home they were usually way oversized. Your furnace should run a lot when it's cold. When It hits design temp (around 0 where I am) it should run all the time
    hot_rodethicalpaul
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,906
    edited December 2022
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    Another thing to consider if your furnace is single stage or multi-stage. If it’s two stage, it’s even more likely to run nonstop - that’s what it’s designed to do. for what it’s worth, my heat loss is 10 btu/sqft in zone 4. Everyone’s house is slightly different. 
  • Waitingfordave
    Waitingfordave Member Posts: 2
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    Thanks, guys. I really appreciate the comments!
  • ethicalpaul
    ethicalpaul Member Posts: 5,761
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    As they said, sq ft is not enough to tell heat load. A compact cape house at 2000 sq ft might have less heat loss than a spread out ranch at 1500 sq ft
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el