HVAC Standby Power Cost Calculator
Estimate how much your HVAC system costs when it’s “off” — also called
standby, phantom,
or vampire power. Add one item (quick mode) or build an itemized list to calculate
kWh and
cost per day / month / year.
Quick reference — typical standby costs
A small always-on load (thermostat + control board, ~8W) costs roughly $11/year.
A seasonal crankcase heater (~60W, 6 months) adds roughly $42/year. Leaving an
ECM blower fan set to “On” (~80W, 24/7) can add roughly $112/year
— often the single biggest standby surprise.
Use the calculator below to add your own components (quick mode for
one load, itemized mode for several), or jump to the
active run cost calculator to compare against actual
heating/cooling costs.
Measure and reduce standby draw:
On this page:
Calculator ·
FAQ ·
Active run cost calculator
What is HVAC standby power?
“Standby” (or “vampire”) power is the electricity an HVAC system uses when it’s not actively heating or cooling.
Many systems keep low-voltage electronics energized 24/7, and some outdoor units run a crankcase
heater
to protect the compressor in cooler conditions.
Common standby sources
- Thermostat and Wi‑Fi radios (always on)
- Control board / transformer standby (low-voltage power supply)
- Outdoor unit electronics (contactors, boards, sensors)
- Crankcase heater (varies by model and conditions)
- Blower / ECM idle (if fan or ventilation modes run)
- Accessories like UV lights, air cleaners, humidifiers, or ventilators
How to measure standby power
For plug-connected components, a plug-in power meter is the easiest option. For whole-system measurement,
a circuit/whole-home monitor can help identify always-on loads.
See energy monitors →
If you find your fan standby is the biggest cost, a
smart thermostat
with circulation scheduling can reduce continuous fan runtime significantly.
Common HVAC standby loads (typical ranges)
These are planning ranges. Real-world watts vary by equipment model,
settings, and accessories.
| Component |
Typical watts |
When it runs |
Notes |
| Thermostat / smart thermostat
|
~1–5 W |
24/7 |
Wi‑Fi models can be slightly higher. |
| Furnace / air handler control
board |
~3–10 W |
24/7 |
Includes low-voltage transformer + controls.
|
| Outdoor unit electronics (heat pump /
AC) |
~2–15 W |
24/7 |
Boards, sensors, relays (varies by
brand/model). |
| Crankcase heater |
~20–150 W |
Seasonal / temperature dependent |
Often the biggest “off” load when active. |
| ECM blower “idle” /
circulation |
~10–80 W |
If fan is set ON or circulation mode |
Running the fan 24/7 can dwarf true standby.
|
| HRV/ERV standby |
~5–25 W |
24/7 standby; higher when running |
See HRV/ERV sizing. |
| Accessories (UV, air cleaner, humidifier controls) |
~5–30+ W |
Often 24/7 |
Check settings and whether it must run continuously. |
What usually costs the most?
- Crankcase heaters (if active for many hours) and fans set to ON are often
the biggest “surprises”.
- Always-on accessories (UV lights, some air cleaners) can be a steady baseline draw.
- True electronics standby (thermostat + boards) is usually small by comparison.
How to measure standby power (practical approach)
- Start with plug loads: use a plug-in meter for any HVAC-related devices that plug into an
outlet.
- Check fan settings: compare thermostat fan Auto vs On (circulation can
add noticeable watts).
- Seasonal checks: re-check in cooling season if you suspect a crankcase heater is running.
- For hardwired equipment: use a circuit / whole-home monitor or ask a qualified tech to
measure safely.
Worked examples (quick sanity checks)
Example A: 8W always-on
8W × 24h/day ≈ 0.19 kWh/day
At $0.16/kWh ≈ ~$11/year
Example B: 60W for 6 months
60W × 24h/day ≈ 1.44 kWh/day
~6 months/year at $0.16/kWh ≈ ~$42/year
Example C: ECM fan 80W, 24/7
80W × 24h/day ≈ 1.92 kWh/day
At $0.16/kWh ≈ ~$112/year
Related tools
Frequently asked questions
What is HVAC standby (vampire) power?
Standby (vampire) power is electricity your HVAC system uses when it is not actively heating or cooling.
Common sources include thermostats, control boards, transformers, crankcase heaters, and accessories that stay
energized.
How do I measure HVAC standby watts accurately?
For plug-connected devices, use a plug-in power meter. For hardwired HVAC equipment, a whole-home or circuit
monitor can help identify always-on loads. Measuring inside panels should be done only by a qualified
technician.
Why does my air conditioner or heat pump use power when it’s off?
Some outdoor units keep electronics energized and may run a crankcase heater to protect the compressor under
certain conditions. Those features can create a steady standby draw even when there is no call for cooling or
heating.
How much does it cost to run a furnace fan 24/7?
It depends on fan type and watt draw (PSC vs ECM), speed, and electricity rate. Enter the fan watts and 24
hours/day in the calculator to estimate daily, monthly, and yearly cost.
How much does a thermostat cost to run per year?
Most thermostats draw only a few watts. Smart/Wi‑Fi models can be slightly higher. Use the calculator with
the thermostat watts and 24 hours/day to estimate annual cost at your $/kWh rate.
What is a crankcase heater and why can it be expensive?
A crankcase heater warms the compressor oil to reduce liquid refrigerant migration. If it runs many hours and
draws tens to over a hundred watts, it can dominate total standby cost during the cooling season.
Is 5–10 watts of standby power normal for HVAC?
Yes. Many systems have small always-on loads from low-voltage transformers and control boards. Larger steady
draws usually come from crankcase heaters, always-on fan modes, or accessories.
Does turning off the breaker save money?
It can eliminate standby draw, but it may disable safety functions and can be unsafe or impractical. Use the
calculator to see whether the standby cost is meaningful before changing how the system is powered.
How can I reduce HVAC standby power?
Start by identifying the biggest always-on source (fan mode, crankcase heater, accessories). Simple fixes can
include correcting fan settings, disabling unnecessary always-on accessories, or servicing controls. For
hardwired changes, use a qualified technician.
Do smart thermostats use more power?
Often slightly more due to radios and displays, but the watt draw is usually small. The calculator can show
whether that difference is meaningful at your local electricity rate.