How Long Will Your House Stay Warm Without Heat?

The furnace quits with the power at 7pm on a January night. The house is 68 degrees and the forecast says 15. The question that decides everything else, including whether you stay or go, is how many hours the house itself will carry you.

The honest answer is a range, because houses differ more than generators do: a typical insulated home loses 1 to 2 degrees an hour in freezing weather at first, and the colder it gets inside, the slower it falls. Most homes are in the mid-40s by the next evening. A tight, modern house can hold livable temperatures for two or three days. An older drafty one can be at 50 before midnight.

The cooling timeline, roughly#

Assumes freezing weather outside and no sun gain. A south-facing window on a clear day genuinely helps; wind genuinely hurts. Your house has one real curve, and the first outage teaches it to you. Write it down afterward.

Shrink the house to one room#

You cannot keep 2,000 square feet warm with no furnace, and you do not need to. Pick the smallest room on the south side with the fewest windows, ideally one you can close off. Then stack the cheap wins in order:

1. Close every door in the house and block the gap under the chosen room's door with a towel.
2. Curtains open in sun, sealed after dark. A blanket over the window frame at night beats the best curtain.
3. Everyone sleeps in the one room. Two adults put out roughly the heat of a small space heater's low setting. In a small closed room, body heat is a real heat source, not a survival-show line.
4. Layer floors and walls with spare blankets and even couch cushions. Cold radiates from surfaces, and insulation works in both directions.

With nothing burning at all, a sealed small room with people in it typically rides 10 to 15 degrees above the rest of the house.

If you add a flame, add it correctly#

The deaths after winter storms are mostly carbon monoxide, and they happen in exactly this situation. The rules are short: only heaters rated for indoor use with an oxygen depletion sensor, a window cracked for fresh air, a working CO alarm in the room, and nothing improvised. An oven is not a heater, a grill is never an indoor anything, and the generator stays outside, 20 feet from windows, even in the snow. If your backup heat burns propane, the same tank math from our generator fuel guide applies to heater run time.

The pipes are on their own clock#

While the living room is still at 45, the pipes in exterior walls can already be at freezing. Once the house passes the low 40s and the cold is staying, switch from comfort to protection: drip the faucets farthest from where water enters, open cabinets under sinks, and if you are leaving, shut off the main and drain the lines. A burst pipe turns an uncomfortable week into a five-figure one.

The fuller winter sequence, including when leaving beats staying, is in the winter storm plan, with the first-hours version in the power outage plan.

Hours come from the house. Days come from the shelf.#

The house decides how many hours you are comfortable. Whether you can simply stay home through a multi-day freeze comes down to what is already on the shelf: food that needs no cooking, stored water before the pipes are drained, light, and layers.

Count yours before the forecast does it for you. Provision Planner turns what is in your pantry and closets into a day count for your household, and shows the gaps while the stores are still open.