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Let cooler evening air in when conditions allow

Cool outdoor air can remove stored indoor heat and sometimes reduce mechanical cooling.

I commit
Miniature scene: Keeping windows closed on a suitable cool evening.
Keeping windows closed on a suitable cool evening
Miniature scene: Using cool clean air with mechanical cooling off.
Using cool clean air with mechanical cooling off
01 / Why this can help

Your scenario, drawn

Cooling with suitable evening air

Cooling with suitable evening airBefore evening ventilation: 80 kWh; With suitable evening ventilation: 60 kWh; Annual difference: -20 kilowatt-hours of electricityIN ONE YEARBefore evening ventilation80 kWhWith suitable evening ventilation60 kWh080 kWh

Same scale, starting at zero. Change the assumptions to compare the two annual totals.

Sources and scope →
Read the values
Before evening ventilation80 kWh
With suitable evening ventilation60 kWh
Annual difference-20 kilowatt-hours of electricity
02 / One possible next step

On a cooler evening, check outdoor temperature, humidity and air quality before using safe openings with the air conditioner off; retain necessary cooling.

03 / Sources and scope

Context-dependent outcome

What the evidence supports

Cool outdoor air can remove stored indoor heat and sometimes reduce mechanical cooling. This is most useful where nights are cool; suitable temperature, humidity and outdoor air quality are essential.

Boundary of the claim

This may not help in hot, humid conditions or during poor outdoor air quality. Use secure openings and keep necessary cooling available. The calculator compares specified electricity inputs; it does not predict indoor temperature or a safe cooling schedule.

What this simulation calculates

2 kWh before, 1.5 kWh after and 40 suitable days are hypothetical inputs, not measured ventilation savings. Include remaining cooling and any fans in the after value. The calculation does not predict indoor temperature or whether outdoor air is suitable.

Published coefficients and calculation references

  • The guidance describes heat removal by suitable cool outdoor air. Cool nights, humidity and outdoor air quality constrain use. It supplies no fixed electricity saving for an open window.

    Natural Ventilation and Cooling ↗

  1. Institutional guidance · U.S. Department of Energy, Building Science Education

    Natural Ventilation and Cooling

    Consulted section (original language): What?; Why?; How?

    Consultation: Webpage / full text

  2. Institutional guidance · U.S. Department of Energy

    Home Cooling

    Consulted section (original language): Opening overview

    Consultation: Webpage / full text

Avoid counting the same change twice

Sources reviewed:

Report a data issue

Other possibilities in this area

At home
Miniature scene: Hang the same laundry in a ventilated room.Let a load of laundry air-dryMiniature scene: Cooling set to 26°C in this example.Find a comfortable, moderate cooling settingMiniature scene: A suitable 30°C wash in this example.Choose a cooler suitable wash
universalizable.At home / 01

Let cooler evening air in when conditions allow

Miniature scene: Keeping windows closed on a suitable cool evening. Miniature scene: Using cool clean air with mechanical cooling off.
Keeping windows closed on a suitable cool eveningUsing cool clean air with mechanical cooling off

Why this can help

Cool outdoor air can remove stored indoor heat and sometimes reduce mechanical cooling. This is most useful where nights are cool; suitable temperature, humidity and outdoor air quality are essential.

One possible next step

On a cooler evening, check outdoor temperature, humidity and air quality before using safe openings with the air conditioner off; retain necessary cooling.

What changes the outcome

This may not help in hot, humid conditions or during poor outdoor air quality. Use secure openings and keep necessary cooling available. The calculator compares specified electricity inputs; it does not predict indoor temperature or a safe cooling schedule.

universalizable.The action / 02

Your illustrative scenario

Over one year · with the assumptions below

You

20 kilowatt-hours of electricity less

You + 10 friends

220 kilowatt-hours of electricity less

1,000 participants

20,000 kilowatt-hours of electricity less

These are scenarios, not measured personal or collective savings. One separate household per participant. People sharing a home count it once, not once each.

Your inputs

Cooling electricity per comparable day before
2 kWh
Cooling electricity per comparable day after
1.5 kWh
Suitable comparable days per year
40

Calculation of the difference: (2 − 1.5) kWh × 40 = 20 kilowatt-hours of electricity

Calculation boundaries

Cooling electricity for the same home over complete comparable days: match weather, temperature setpoint, occupancy and comfort. Include extra lighting or ventilation fans. Unmatched meter readings do not establish an effect of this action; maintain necessary cooling.

2 kWh before, 1.5 kWh after and 40 suitable days are hypothetical inputs, not measured ventilation savings. Include remaining cooling and any fans in the after value. The calculation does not predict indoor temperature or whether outdoor air is suitable.

Sources and calculation references

  1. Natural Ventilation and CoolingU.S. Department of Energy, Building Science Education
  2. Home CoolingU.S. Department of Energy

Read the method: universalizable.com/en/method/ · One sheet · print double-sided, long-edge binding

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