btuh vs btu per square foot

Waitingfordave

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.

GroundUp

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

There’s no simple btu/ft for sizing. If your furnace keeps your house at temp, you’re properly sized. Likely oversized.

EBEBRATT-Ed

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_water_fan

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

Thanks, guys. I really appreciate the comments!

ethicalpaul

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