In January, soon after I learned about Beestat, our house’s balance point was 34F, so that’s where I set the AUX heat to come on. Today I checked it again and based on information through April 13, it was shown as 24F. That’s great and I reconfigured AUX heat accordingly. But what accounts for that large a change? Is Beestat just more accurate now that it has 35 weeks of data to rely on? The only actual improvement in the house since January was that we constructed a new attic hatch. The hatch had previously been just a piece of uninsulated drywall, which the HVAC crew had stepped on (so it was a broken piece of drywall). The new hatch has weatherstripping and eight inches of rock wool. Could it make that much of a difference?
I’m sure it made a difference, but probably not 10°F of difference. I would put my money on that, plus additional data doing a better job of capturing your actual balance point throughout January/February. More data generally always produces a better result.
Jon, does balance point (Heat delta) take Aux heating out of the equation or does it include all heating? If it doesn’t remove Aux, then the balance point will go lower due to the additional heating source. For a true balance point for a heat pump, it can’t include the Aux.
Mary Kaye, you may find that 24F is too low a threshold to set Aux heat at. My personal suggestion from this winter’s experience is to look at where your Heat delta is +1F/hr and set Aux there. I suspect it will be in the 30-34F range. Right around where you had it originally set. It’s also a good idea to use Ecobee’s Smart Recovery to help minimize Aux use when your set temp changes by 3 degrees or more, like from Sleep to Home.
Balance points calculate independently for both heat stages and do not include aux heating.
Thanks, Jon. Haven’t seen those graphs before. I’m guessing that you remove times when Aux is running from the balance point calcs. 
My balance point calcs will be off, on one home, as I used a gas fireplace during peak electric rates and temps that would cause Aux heat to kick in. Interestingly on another home, I am seeing a balance point of 0F but the Heat delta graph shows 18F as the balance point. I’m guessing that you use a longer data frame than the graph’s 17 weeks. I’m more inclined to believe the 0F, as it is an old New England house with a steam boiler and have seen the home maintain at well below 0F.
As for Mary Kaye, I still recommend either setting Aux at the point where you drop at or below a Heat delta of +1F/hr or at the point where Heat delta = Resist delta. If you use any setbacks, it will take a long recovery time running just the heat pump. Setting the Aux Heat Max Outdoor Temp threshold around one of those will give you a better balance between runtime & cost. Even if you set it high, Aux heat will only run based on the Aux Savings Optimization setting, default of 2.9F. But, at a high Aux max outdoor temp setting, the Aux may run on any setback recovery 
. Time/experience with the system will help you find when it is best to have Aux heat available vs. strictly metrics. If it never setbacks, it isn’t an issue. But, if you use any -3F or greater setbacks Sleep, Away, etc., then you’ll want Aux heat available below a certain Heat delta. At a heat delta of +1F, it will take 3hrs for the heat pump to recover from a 3 degree setback. That can be a long time to have to wait to feel warm.
1 Like