Why You Won’t Die In The Winter Without Central Heat. Probably.

The other day I was checking on some gear stored in my detached garage and noticed something I’d seen in previous winters: It was about 25 degrees outside, but my thermometer inside the garage read 45 degrees. That’s a 20 degree difference, and my garage isn’t even insulated. Just four walls, a concrete slab, and double garage doors facing southwest.

This got me thinking about grid down scenarios in winter. Most people assume that if the power goes out for an extended period during cold weather, their house will quickly drop to outdoor temperatures and they’ll be in serious trouble. But that’s not how it actually works.

Why Your Home Stays Warmer Than You Think

There’s real science behind why enclosed structures maintain higher temperatures than the surrounding air. My garage is proof of this; several factors are at play.

First, there’s thermal mass. Concrete slabs, drywall, furniture, stored items, even the lumber in your walls absorbs heat during warmer periods and releases it slowly. This mass acts like a battery, moderating temperature swings. Your home probably has more thermal mass than my relatively sparse garage, which means it will hold heat longer than you might expect.

Wind protection matters more than most people realize too because wind accelerates cooling dramatically. When you’re inside a structure with closed doors and windows (with appropriate weatherstripping, doors seals, etc.), you eliminate wind chill entirely. The air inside loses heat much more slowly than the constantly moving air outside.

Then there’s reduced air exchange. An enclosed space with weatherstripping and closed doors doesn’t continuously flush warm air out and pull cold air in. In fact, every gap you seal improves this effect. I can tell you from experience that fixing even the smallest gap between my front door and the door casing made a huge difference in the amount of cold air that gets in.

Solar gain helps even in winter. South and west facing windows, in particular, capture sunlight and convert it to heat. My metal garage doors face southwest and get afternoon sun, which explains some of that 20 degree temperature boost. Thankfully, your home probably has more windows and better positioning to capture this free heat.

Finally, insulation and structure provide protection. Even minimal insulation in walls and attics (and even having an attic) slows heat loss considerably. Your home was designed to retain heat, unlike my garage.

Our basement is worth mentioning here. Because most basement walls where I live (in the Midwest) are partially or fully underground, they benefit from stable soil temperatures. Earth a few feet down stays around 45 to 55 degrees year round in most regions, though I’m sure those in the northern latitudes can get colder during the dead of winter. Regardless, this means basements typically remain the warmest part of an unheated home during winter.

Temperature Thresholds: What Can You Actually Survive?

Understanding what temperatures are dangerous helps you plan appropriately. While the human body maintains a core temperature around 98.6 degrees, hypothermia begins when your core drops to 95 degrees. That doesn’t sound like much difference, but it is.

Unfortunately, it’s a constant battle against the elements. Even indoors, your body loses heat to cold floors, cold air, and cold surfaces. Over time, your metabolism can’t keep up. Things get worse as you get older (and as my father-in-law will vehemently testify to).

Here’s what the research shows for indoor survival without wind or rain from what I can gather…

Above 40 degrees, the average adult can likely survive indefinitely with adequate clothing and the ability to move around. Between 32 and 40 degrees, most people can survive for days with proper home insulation, clothing, etc. From 20 to 32 degrees, you’re looking at many hours to possibly a day or two if you’re well insulated. Below 20 degrees becomes dangerous within hours unless you have serious additional insulation like cold-rated sleeping bags. Below 10 degrees is life threatening within one to three hours even indoors and without proper gear. Below zero is lethal quickly without serious insulation, clothing, etc.

These numbers assume you’re at rest with minimal clothing and you’ve taken no additional steps to keep warm. You should add layers, hats, gloves, blankets, and sleeping bags to extend your survival time dramatically. A quality sleeping bag alone can mean the difference between dangerous and manageable, though you probably won’t get much done if you’re stuffed in a bag much of the day.

Real world examples back this up. During World War II, civilians survived in basements and cellars at 20 to 35 degrees for weeks using blankets, straw, and body heat. Homeless populations in northern cities regularly survive 10 to 25 degree nights with sleeping bags and at least some basic shelter. The key in every case was insulation everywhere, not ambient temperature.

The most vulnerable people deserve special consideration, however. Elderly people, young children, and those with health conditions cannot regulate body temperature as effectively as healthy adults. They’ll struggle at temperatures where you might be merely uncomfortable. If you’re planning for family, plan for the weakest member!

Given typical home construction, if your power goes out in winter, your house will cool slowly. Over a few days in normal winter weather, interior temperatures might drop into the 30s or 40s. Over weeks in severe cold, it could approach outdoor lows, especially in drafty rooms. But your basement will likely stay in the 30s to 40s throughout.

Granted, this is typical for where I live in Kansas City; your situation will vary based on climate, duration of living without power, home construction (insulation, earth-backed or not, drafts, etc.), what you do to stay warm, and personal tolerances.

It’s also important to consider your utilities during this endeavor, as water pipes in particular will certainly freeze and burst when it eventually warms up. About the best you can do if you’re not actively heating your home is to turn off the main water into your home and drain all interior water pipes. You’ll also want to flush toilets and remove as much water as possible to avoid cracking the porcelain.

Unconventional Ways to Keep Warm

Beyond the obvious solutions like wood stoves and propane or kerosene space heaters, there are passive methods that require no fuel and minimal expense. These won’t make your home toasty, but they can raise indoor temperatures by several critical degrees.

Cover your windows with bubble wrap. The air pockets provide insulation while still letting light through. Cut it to size and spray water on the window, then press the bubble wrap flat against the glass. It sticks surprisingly well and can reduce heat loss by, some say, 50 percent. When the sun’s out, you might remove the bubble wrap from south facing windows to capture solar gain, then replace it at night. Or find other ways to reduce heat loss through windows with cardboard, tape trash bags over the casings, cover with bedding or anything to slow heat loss.

Use water jugs or barrels for thermal mass. Water stores heat better than almost any common material. (This might be one small reason why my garage stays a bit warmer because I keep eight 55-gallon drums there.) Fill dark colored containers with water and place them where they’ll receive direct sunlight. Five gallon buckets will work great, and they’re manageable. As the sun warms the water during the day, it absorbs massive amounts of heat energy. At night, that heat slowly releases, moderating the indoor temperature. People using this method in greenhouses report raising nighttime temperatures by 5 to 10 degrees.

Paint surfaces dark colors where sun hits them? Dark brown or dark green surfaces absorb 80 percent of solar energy. Shiny white or light colored surfaces, however, only absorb 15 to 20 percent. If you have a concrete basement floor (which is usually light grey) that gets sun through a window, you might consider painting it a dark color to increase heat absorption. But it probably won’t do much good. Instead, move/use dark colored items, such as furniture, books, carpet, dark buckets of water, or whatever to absorb heat.

Layer rugs and blankets on floors. Cold floors suck heat from your body faster than almost anything else indoors. Carpet remnants, old blankets, cardboard, even newspapers create an insulating layer between you and the cold floor, just like a sleeping pad insulates you and your sleeping bag if you’ve ever been winter camping. Remember: the thicker the better. In fact, this single change can make a room feel 5 to 10 degrees warmer.

Hang blankets or sleeping bags on exterior walls. We talked about windows, which are a massive source of heat loss in modern homes, but your walls lose heat to the outside as well. Adding another layer creates an air gap that acts as insulation. This is especially effective on walls that don’t have proper insulation or that face prevailing winds. Thick moving blankets or old something similar work best, but anything you can add to reduce heat loss is acceptable. In fact, if I got desperate enough, I might pull all the carpet from my upstairs floors and use them to either line the cold basement floors or hung up near the walls.

Close off unused rooms entirely. Every room you heat is energy wasted. Pick one or two rooms on the sunny side of your house, seal them off with plastic sheeting or closed doors, and concentrate your efforts there because smaller spaces are easier to keep warm with body heat and passive methods. That said, you do need to consider airflow and egress (the ability to escape) because it can get stuffy, moldy, and dangerous if you attempt too much.

Block drafts aggressively. Like I said previously, air leaks around doors, windows, and even electrical outlets and plumbing waste tremendous amounts of heat. Weatherstripping, draft stoppers, plastic film over windows, and towels stuffed in gaps make a measurable difference. Walk around your house on a cold and windy day with a lit candle and watch where the flame flickers. Or place your hand near suspected problem areas and you’ll find the source. And remember not to use an open flame around gas or propane!

Use furniture strategically. Heavy furniture acts as thermal mass and also blocks drafts. For example, a bookshelf full of books against an exterior wall provides both insulation and thermal storage. You could, similarly, arrange furniture to create smaller, protected spaces within larger rooms.

Reflective materials can redirect heat. Emergency blankets (the shiny mylar ones that I generally detest) or the shiny side of aluminum foil placed behind heat sources reflect radiant heat back into your living space instead of letting it seep into the rest of the house. These items are cheap and surprisingly effective for their weight. To increase resistance to rips and tears, line cardboard or other large, flat material with the Mylar blankets or foil.

A simple candle heater won’t heat your whole house, but it can warm a small space. Place a tea candle on a brick or tile or metal baking sheet, then invert a terracotta pot over it. The pot absorbs heat and radiates it outward while keeping you, pets, and children safer. This is a supplemental heat source at best, but it’s better than nothing and requires minimal supplies.

What This Means for Preparedness

The takeaway here is that your home provides more protection than you probably realized. You won’t maintain 70 degrees without active heating, but you also won’t immediately drop to outdoor temperatures. With passive methods and proper clothing, indoor survival at 30 to 40 degrees is realistic for extended periods.

Clearly, your preparation should focus on passive insulation techniques, not just heat sources like a wood stove or space heaters. Quality sleeping bags rated for temperatures well below freezing are wise. If you can’t afford these, consider keeping old comforters and blankets or anything that can be used to add insulation. Layers of clothing, particularly wool and synthetic materials that insulate when damp are good to have. Heavy blankets, rugs, and materials to block drafts, like I mentioned earlier, should be used strategically.

You could even test your space now while you still have heat. You might, for instance, turn off your furnace for 24 hours on a cold day and see what happens, measuring temperatures in different rooms. Identify drafts. Learn which rooms stay warmest. This information will be valuable when you actually need it. Of course, pay attention to special problem areas, like water pipes to ensure they don’t burst, water or food storage (which could break the can seals thus spoiling the food or burst water bottles), and walls that may condensate and cause mold or mildew problems.

I’ve written about winter preparation strategies before, and if you’re considering off grid living, this article on preparing for winter without grid power covers additional considerations.

The reality is that most winter emergencies won’t be weeks or months long. They’ll be a few hours or maybe a couple days in most cases. Your home’s natural thermal properties, combined with passive heating methods and proper insulation, can carry you through that period safely without much worry. And if things stay bad for longer, you’ll have some idea of what you can do to keep from freezing.

Thoughts?