Ecobee Auxiliary Heat Running Too Much? DIY Setting Threshold Fix That Actually Works

The first time I saw this problem, a homeowner had been running their aux heat almost continuously for three days straight — their electric bill was going to be brutal. Turned out the Ecobee threshold was set wrong right out of the box, and nobody had touched it. I’ve pulled dozens of service calls since then for the exact same reason, and every time, it came down to one or two settings that most people don’t even know exist.

If your Ecobee auxiliary heat is running too much, this guide is specifically about DIY setting threshold adjustments you can make today — no HVAC license required. Let’s dig in.

What Is Auxiliary Heat and Why Does Your Ecobee Control It?

Auxiliary heat is the electric resistance backup that kicks in when your heat pump can’t keep up with demand alone. Your Ecobee is supposed to manage when it turns on — and for how long.

Heat pumps are efficient down to a point. Below a certain outdoor temperature — usually around 35°F to 40°F depending on equipment — the refrigerant cycle loses efficiency fast. That’s when auxiliary heat (also called emergency heat or strip heat) takes over or supplements.

Your Ecobee doesn’t just blindly run aux heat. It uses outdoor temperature data, the differential between setpoint and actual indoor temperature, and a user-configurable threshold to decide when aux heat activates. The problem is that the default settings are often too aggressive. Ecobee ships the thermostat with conservative defaults that prioritize comfort over efficiency — and that means aux heat gets called way too early and runs way too long.

Recognizing the “Auxiliary Heat Is Running Too Long” Alert

Ecobee has a built-in alert that triggers when aux heat runs beyond a time threshold you set. Most homeowners either ignore this alert or don’t know how to respond to it.

The alert reads something like: “Auxiliary heat is running too long.” It shows up in the Ecobee app or on the thermostat display. When you see this, the thermostat is telling you that aux heat has been active longer than whatever limit you’ve configured — or longer than the default if you’ve never touched it.

This matters. The alert isn’t cosmetic. It’s a diagnostic flag.

There are two scenarios here: either your aux heat threshold is set too short (false alarm, normal operation triggering the alert), or your system genuinely has a problem causing extended aux heat runtime. I’ll address both, but I want to start with the settings fix because that’s what resolves 70% of these calls.

How to Adjust Your Ecobee Auxiliary Heat Running Too Much DIY Setting Threshold

This is the core fix. Adjusting the aux heat threshold in your Ecobee settings directly controls when the alert fires and — more importantly — how aggressively aux heat is used.

Here’s exactly how to do it:

On the Ecobee thermostat display:

Tap the menu icon (three horizontal lines)
Go to Settings
Select Installation Settings
Tap Thresholds
Find Aux Heat Max Outdoor Temp and Compressor to Aux Temp Delta

Via the Ecobee app (phone or web):

Open the Ecobee app
Tap your thermostat, then go to Settings > Preferences
Scroll to threshold settings under HVAC

The two settings that matter most:

Aux Heat Max Outdoor Temp: This is the outdoor temperature above which aux heat will NOT run. Default is often set to 40°F. I recommend bumping this down to 35°F or even 30°F if your heat pump is properly sized and your home is reasonably insulated. This alone can cut aux heat runtime by 30–40%.
Compressor to Aux Temp Delta: This is the temperature differential required before aux heat kicks in alongside the heat pump. Default is often 1°F or 2°F — way too sensitive. Set this to 3°F–5°F. Your heat pump should be doing the heavy lifting. Only bring in aux when the heat pump is clearly losing ground.
Aux Heat Runtime Alert Threshold: This is the timer that triggers the alert. If you’re running longer heat cycles legitimately (very cold climate, larger home), bump this from the default (often 3 hours) up to 5–6 hours so you stop getting false alerts.

After looking at dozens of cases, the Compressor to Aux Temp Delta setting is almost always the culprit when aux heat is cycling on every single heating call instead of only during extended cold snaps.

Quick Fix vs. Permanent Fix

There’s a difference between stopping the bleeding today and solving the root problem. Here’s how to separate the two.

Quick Fix (Do this right now):

Raise the Aux Heat Runtime Alert Threshold so the alert stops firing while you diagnose. Then lower the Aux Heat Max Outdoor Temp by 5°F and raise the Compressor to Aux Temp Delta to 4°F. Monitor for 24–48 hours.

Permanent Fix:

The permanent fix involves confirming your heat pump is actually functioning at spec — not just adjusting the thermostat to hide a mechanical problem. Check refrigerant charge (a low charge kills heat pump efficiency fast), verify your air filter isn’t clogged (restricted airflow makes the system work harder), and confirm your outdoor unit coil isn’t iced over. If the heat pump is healthy, the threshold adjustments above will stick long-term.

I’ve seen this go wrong when a client adjusted thresholds but had a refrigerant leak. The aux heat kept running because the heat pump literally couldn’t produce enough heat. They adjusted the Ecobee three times before calling me. The real fix was a refrigerant recharge — $280 instead of months of inflated electric bills.

Here’s What I’ve Seen Go Wrong in the Field

Field experience cuts through theory. These are real patterns I’ve diagnosed repeatedly, not textbook scenarios.

Case 1 — The builder-grade default trap: A client moved into a new construction home with an Ecobee already installed. The builder’s HVAC sub had left every threshold at factory default. The Aux Heat Max Outdoor Temp was 40°F. In their climate (mid-Atlantic), temps dropped into the low 40s almost every night from October through April. Their heat pump was a 3-ton Carrier with good cold-weather specs — it could handle 38°F easily. But the Ecobee was calling aux heat every single night. Three threshold changes, done in ten minutes, dropped their electric bill by $90 the following month.

Case 2 — The “it worked fine last year” problem: A homeowner called me in January saying their Ecobee aux heat suddenly started running much more than the previous winter. Same settings, same house. What changed? The outdoor unit’s defrost board was sticking — the unit was spending too much time in defrost mode, which tanks heating output and forces the Ecobee to call aux heat to compensate. The thermostat was doing exactly what it was supposed to do. The fix was a $45 defrost control board, not a thermostat setting.

The turning point is usually when you ask: did this behavior change recently, or has it always been like this? If it changed, look at mechanical issues. If it’s always been like this, it’s almost certainly a threshold setting problem from day one.

When Aux Heat Running Long Is Normal (And When It’s Not)

Not every long aux heat cycle is a problem. Knowing the difference saves you time and prevents unnecessary service calls.

Normal scenarios:

Outdoor temps below 25°F — heat pumps lose significant capacity here, aux heat carrying load is expected
Recovery from setback — if your schedule drops temp 5°F+ overnight, recovery in the morning will lean on aux heat
First heat of the season on a cold day — the house is cold-soaked, aux heat will run harder initially

Not normal — investigate further:

Aux heat running at 45°F+ outdoor temps (heat pump should handle this alone)
Aux heat running but indoor temp still dropping
Aux heat cycling on and off rapidly (short-cycling)
Alert fires every single day regardless of outdoor temp

For deeper HVAC troubleshooting logic and threshold diagnosis frameworks, there’s solid structured guidance worth bookmarking.

Ecobee Threshold Settings Reference Table

Here’s a summary of the key settings we covered, what the defaults typically are, and what I actually recommend based on field experience.

Setting	Default Value	Recommended Value	Effect
Aux Heat Max Outdoor Temp	40°F	30–35°F	Prevents aux from running when heat pump can handle the load
Compressor to Aux Temp Delta	1–2°F	3–5°F	Requires larger temp gap before aux kicks in alongside compressor
Aux Heat Runtime Alert Threshold	3 hours	5–6 hours (cold climates)	Reduces false alerts while still flagging genuine overruns
Heat Differential Temp	0.5°F	1–2°F	Reduces short-cycling by allowing wider swing before heat call
Minimum Compressor Runtime	5 min	5–10 min	Ensures heat pump runs long enough to be productive before aux backup

FAQ

Why is my Ecobee calling aux heat when it’s 45°F outside?

Your Aux Heat Max Outdoor Temp is almost certainly set too high — likely 40°F or 50°F default. Drop it to 30–35°F. At 45°F, a properly functioning heat pump should be handling the load alone. The DIY Stack Exchange community has documented this exact issue with multiple Ecobee owners hitting the same default-setting trap.

Can adjusting Ecobee threshold settings void my warranty?

No. These are user-configurable settings exposed in the Ecobee interface by design. You’re not modifying hardware or bypassing safety controls. Ecobee explicitly allows homeowners to adjust these thresholds. The only thing that could affect your HVAC equipment warranty is improper wiring or bypassing manufacturer safety controls at the unit level — not thermostat threshold settings.

How long should aux heat actually run per cycle?

In normal operation above 30°F, aux heat cycles should be short — 10 to 30 minutes maximum during recovery from setback, or brief supplemental bursts during sustained cold. Continuous aux heat running for 1+ hours at temps above 35°F is a red flag. Below 20°F outdoor temps, extended aux heat runtime (2–4 hours on the coldest days) can be normal depending on your home’s heat loss rate and equipment sizing.

References

The real insight here is this: your Ecobee isn’t broken, and your heat pump probably isn’t either. The factory defaults were written to satisfy comfort complaints, not efficiency goals. When you adjust the threshold settings yourself, you’re not hacking anything — you’re finishing a configuration job that the installer should have done on day one.

Ecobee auxiliary heat running too much DIY setting threshold