Staged Auxiliary Heat

Staged Auxiliary Heat

Staged Auxiliary Heat lets your Mysa Smart Thermostat automatically engage auxiliary heating when your heat pump can't reach the setpoint on its own. Instead of manually switching to Aux/Emergency mode on cold days, the thermostat handles it for you based on temperature and runtime thresholds you configure.

This feature is off by default and only appears for system configurations that support auxiliary heat.

How It Works

The thermostat monitors two things:

1. Temperature difference — How far the room temperature is from your setpoint
2. Runtime — How long the heat pump has been running trying to reach the setpoint

When either threshold is exceeded, auxiliary Stage 1 engages automatically.

For electric auxiliary heat: The compressor keeps running alongside the aux heat.

For gas or oil auxiliary heat: The compressor stops and aux runs alone. When aux turns off, there's a 2-minute delay before the compressor restarts (the fan continues running during this time).

Configurable Settings

You can adjust these thresholds in the app. Values use 0.5°C and 5-minute increments.

Stage 2 Heating (Heat Pump)

• heat2delta — Temperature difference that triggers Stage 2 heating (default: 2°C / 3.6°F, range: 0.5–5°C)
• heat2DelayMinutes — Runtime before Stage 2 kicks in (default: 20 min, range: 10–120 min)

Auxiliary Stage 1

• aux1delta — Temperature difference that triggers aux heat
  • Electric aux default: 1.5°C (2.7°F)
  • Gas/Oil aux default: 2.0°C (3.6°F)
  • Range: 0.5–5°C
• aux1DelayMinutes — Runtime before aux kicks in
  • Electric aux default: 40 min
  • Gas/Oil aux default: 60 min
  • Range: 10–120 min

Stage 2 Cooling

• cool2Delta / cool2DelayMinutes — Same staging model applies to cooling systems with two stages

Short Cycling Protection

To protect your equipment and improve efficiency, the thermostat enforces minimum run times and delays:

• At least a 5-minute gap between aux cycles
• For gas/oil aux, a 2-minute reverse-staging delay before the compressor restarts after aux turns off (fan runs during this delay)
• Electric aux can run simultaneously with the compressor, so no reverse-staging delay is needed

Manual Aux/Emergency Mode

If you manually set the thermostat to Aux/Emergency mode (from the device or app), automatic staging defers to your manual selection. The automatic staging logic won't override manual emergency mode.

Note The EMERG indicator on the thermostat display only appears when you've manually engaged Aux/Emergency mode. Automatic staging doesn't show this indicator—it works in the background.

Choosing Your Auxiliary Type

When setting up staged aux heat, the app will ask what type of auxiliary heating you have.

Caution Selecting the wrong auxiliary type can cause inefficient or potentially damaging behavior. If you're unsure whether you have electric, gas, or oil backup heating, choose "I don't know"—the app will use a safe default that doesn't run the heat pump and aux simultaneously.

Troubleshooting

Aux didn't engage when I expected it to

Check that:

• Staged Auxiliary Heat is enabled
• Both the temperature difference AND runtime thresholds were met
• The app displays rounded values for convenience, but the thermostat uses precise values internally—borderline cases may behave slightly differently than expected

Temperature readings seem off

If sensor readings are incorrect, the staging logic may not engage aux when needed. Check your thermostat's temperature readings against a separate thermometer. Contact support@getmysa.com if readings are significantly off.

Related Articles

• Thermostat Configuration
• HVAC Configuration Code
• Freeze Protection