The short answer
In a freeze, heat is the load that ruins the plan: a 1,500 W space heater drains a 2,000 Wh battery in about an hour. Plan for the loads that keep a house livable — a furnace blower, refrigerator, internet and phones — keep batteries inside the temperature range their maker states, and keep generators outdoors.
Cold and batteries
- Makers state a temperature range for discharging and a narrower one for charging; many lithium batteries should not be charged below freezing. Check the specification page for your model.
- Keep a battery inside the heated space during use. A cold battery delivers less than its rated capacity.
- Solar charging in a freeze is possible but limited by short days and snow cover; do not rely on it alone.
Practical noteCold-weather capacity loss is real but varies by chemistry and model. Wattstanding does not publish a cold-weather derating figure because makers do not publish a consistent one.
What to power
| Load | Typical running watts | Average with cycling | Comment |
|---|---|---|---|
| Gas furnace blower | 750 | 375 | Needs the furnace's gas and ignition to work; the blower only moves air |
| Refrigerator | 150 | 60 | In a freeze, an outdoor-cold pantry may do part of its job |
| Router and modem | 25 | 25 | Keeps phones and alerts working |
| Space heater | 1,500 | 1,500 | Continuous; too much for most batteries |
| Phones and tablets | 40 | 40 | Highest value per watt |
Total your own list with the load calculator. For a multi-day freeze a generator with a transfer switch or interlock, installed by a licensed electrician, is the common route for heavy loads.
Generators in the cold
- Run generators outdoors, away from the house, with the exhaust pointed away; keep snow and ice away from the exhaust and any enclosure.
- Cold-start performance varies; check the maker's guidance for oil and fuel in low temperatures.
- Propane keeps working in cold weather better than many people expect, but tanks must be sized and placed correctly; natural gas depends on the line.
SafetyCarbon monoxide poisoning is a leading danger in winter outages. Never run a generator in a garage or near windows, and have working CO alarms.
Figures marked as Wattstanding calculations show their working; product figures come from the sources on each product page. How we work