Is degree day based on 65 degrees avg or resist balance point?

Is the degree day metric 65 degrees (F) or based on the house’s resist balance point? I’ve seen arguments for either one.

It’s not really a big deal either way, but I ask because right now during the summer I’ve been able to slowly increase my house’s balance point to 68 degrees, hoping to get it as high as I can (up until the low 70s).

BTW, as I learn more about my house’s heating/cooling needs (thanks to beestat!), the latest thing I realized was how to use the balance point data. As my main concern is lowering cooling costs (especially now in the summer), it took a while to realize that one would want a higher resist balance point to help cool the house down faster (up until, I assume, one’s actual desired comfort temp).

I recently got a whole house fan to take advantage of California’s (so far) cool evenings, opening all the windows as soon as the temps outside are lower than the temps inside, and closing them again immediately in the morning when the differential inverts again. I’ve been able to cut my runtime per degree day to 1/3rd of last years.’

Thanks again!

It’s based on 65°F. I like using your home’s resist balance point but that makes it difficult to do accurate comparisons so I opted for the standard. Glad to see you’ve been able to cut runtime…that’s pretty a pretty impressive reduction!

No worries, and totally makes sense! As for my runtime, last year WAS inflated due to everyone in my household being home all the time due to the lockdowns, but I’m still calling it a huge win. I had JUST downloaded all my ecobee info myself and excel was getting crushed from the CSV data and was taking forever graphing it in a digestible way. I discovered beestat at the perfect time.