Temperature Setback Calculator

Calculator

Units

Choose the temperature unit you work with.

Calculation mode

Detailed is best for greenhouse planning.

Outside average during setback

Use a typical night-time average for your season.

Baseline setpoint (no setback)

Your normal target temperature for those hours.

Setback setpoint

Lower setpoint used to reduce heating demand.

Setback hours per day

Common range: 6–12 hours at night.

Days per week using setback

Set to 0 for off-season.

Greenhouse area

m²

Floor area is a practical starting point.

U-value (heat transfer)

W/m²·K

Typical range: 3–6, depending on glazing.

UA override (optional)

W/K

Use if you already know overall heat loss coefficient.

Heating efficiency

Example: 0.85 for 85% efficient heating.

Energy price

/kWh

Use your billed rate for electricity or heat energy.

Currency code

Example: USD, PKR, EUR, GBP.

Notes (optional)

Reset

Example data table

Scenario	Baseline	Setback	Outside	Hours/day	Area	U-value	Efficiency	Price
Leafy greens (cool season)	18°C	14°C	6°C	10	60 m²	4.0	0.85	0.25 /kWh
Tomato transplants (gentle setback)	22°C	19°C	10°C	8	80 m²	3.5	0.90	0.30 /kWh
Tropical ornamentals (minimal setback)	26°C	24°C	18°C	6	40 m²	5.0	0.80	0.28 /kWh

These example values are illustrative. Tune inputs to your crop sensitivity, humidity control, and local climate.

Formula used

Heat loss coefficient: UA = Area × U-value (or enter UA directly).

Setpoint reduction: ΔT = Baseline − Setback.

Delivered heat saved: kWh_saved = (UA × ΔT × Hours) ÷ 1000.

Cost saved: Cost = (kWh_saved ÷ Efficiency) × Price_per_kWh.

Detailed mode estimates percent reduction during setback hours using outside temperature. Simple mode provides a fast, conservative estimate.

How to use this calculator

Choose your units and select a calculation mode.
Enter baseline and setback temperatures for your greenhouse.
Add your outside average during setback hours for better accuracy.
Provide setback hours per day and how many days per week you apply it.
Enter greenhouse area and an estimated U-value, or override UA.
Set your heating efficiency and energy price, then calculate.
Download CSV or PDF to keep a seasonal operating record.

Temperature setback as an energy lever

Reducing the heating setpoint for a planned window cuts heat loss almost linearly with the temperature drop. A 4°C setback applied 10 hours per night over seven days equals 70 setback hours weekly. This calculator converts that window into kWh using your heat-loss estimate, helping you compare different schedules before changing the controller.

Why UA matters more than floor area alone

Heat loss is governed by the overall heat-loss coefficient, UA (watts per kelvin). A small house with poor glazing can have higher UA than a larger insulated structure. Typical single-layer plastic is often near 5–6 W/m²·K, double poly near 3–4, and multiwall panels commonly around 2–3. Air leaks can effectively increase UA.

Outside averages and realistic scheduling

Detailed mode uses an outside temperature during setback hours because savings depend on the difference between inside setpoints and outdoor conditions. If nights are mild, a large setback may save little but can increase humidity risk. If nights are cold, even a modest setback yields strong savings. Use a seasonal night average, not a daytime forecast.

Interpreting kWh and cost outputs

Delivered kWh saved is the heat no longer needed by the space. Billed kWh saved adjusts for heater efficiency, so a 0.80 efficiency means you purchase 1.25 kWh for each delivered kWh. Multiply billed kWh by your local energy price to estimate weekly savings, then scale to monthly by multiplying by about 4.3 weeks. For fuel systems billed in therms or liters, convert to kWh equivalents using your supplier factor, then keep the same workflow across seasons and crops.

Crop safety, condensation, and control limits

Use setbacks that match crop tolerance and disease pressure. Seedlings and tropical ornamentals usually need tighter temperature bands than cool-season greens. Monitor dew point, ventilation, and circulation during cooler periods. If condensation rises, shorten setbacks, raise the setback setpoint, or stage the change gradually to avoid plant shock and heater cycling.

What is a temperature setback in greenhouse growing?

A temperature setback is a planned period where the heating setpoint is lowered, usually overnight. The goal is to reduce heat loss while keeping crops within safe temperature limits.

Which mode should I use for planning?

Use Detailed mode when you have a reasonable night outside average, because savings depend on outdoor conditions. Use Simple mode only for quick comparisons when outside data is not available.

How do I choose a U-value?

Start with the glazing type: single layer is often higher, double layers lower, and multiwall panels lowest. If you have an energy audit or past heat data, enter UA directly for better accuracy.

Why does efficiency change the cost result?

The delivered heat saved is what the greenhouse no longer needs. If your heater is not 100% efficient, you must buy more energy to deliver that heat, so the billed savings are larger than delivered savings.

Can setbacks increase humidity or disease risk?

Yes. Cooler air can raise relative humidity and promote condensation on leaves and structure surfaces. Maintain airflow, manage ventilation, and avoid setbacks that push the crop near its dew point.

How can I validate the estimate?

Log inside temperature, outside temperature, and energy use for a week with and without setbacks. Adjust UA or efficiency until the calculator matches your measured consumption, then reuse the tuned values.