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Heating & cooling
What to set the thermostat to, heat pump or furnace costs where you live, what a space heater really costs, how humid to keep the house before windows fog, and when pipes are at risk of freezing.
- 6 guides
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- Reviewed Oct 3, 2026
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Home Energy Guide
What Humidity Should a House Be in Winter? 30–40%, Lower on Cold Nights
About 30–40% relative humidity, inside EPA’s 30–50% range, and lower on the coldest nights. Our NOAA estimate of when windows fog in 20 US cities, plus signs of air that is too dry or too damp.
Home Energy Guide
Calculator
How Much Does It Cost to Run a Space Heater? Costs by State and City
A 1,500-watt space heater costs about 27¢ an hour at the 2026 US average electricity price. Costs by state and in 20 cities, and how its heat compares with a furnace or heat pump.
Home Energy Guide
What Temperature to Set Your Thermostat in Winter: 68°F, Then Lower at Night
About 68°F while you are awake and 7–10°F lower at night for a furnace or boiler; a heat pump stays steady. What a setback saves in 20 US cities, plus the 55°F and health floors.
Home Energy Guide
Calculator
At What Temperature Do Pipes Freeze? The 20°F Threshold and Where It Hits
Pipes in unheated spaces are most at risk at about 20°F outside, per a University of Illinois study. How often 20 US cities get there, and what to do before a freeze.
Home Energy Explainer
Do Heat Pumps Work in Cold Weather? What the Data Says
Cold-climate heat pumps keep at least 70% of their capacity at 5°F. How cold 21 US cities get, from NOAA normals and design temperatures, plus field results.
Home Energy Comparison
Heat Pump vs Furnace: Which Is Cheaper to Run Where You Live
A heat pump beats a gas furnace on running cost only when its COP tops a break-even set by your rates. Estimates for 20 cities, the formula, and a lookup table.
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