Can You Run a Propane Heater Indoors? The Red Cross and the Manual Don't Agree.

Last winter we had the coldest stretch in a long time, single digits for over a week. Of course our furnace failed while I was held at work for the blizzard, and the house had no heat while we waited on a part.

My wife ran the oil-filled heaters and Dreo electric heaters in each room, and they kept the inside temperature in the low 70s until the part came in. No flame, so no carbon monoxide from the heaters themselves.

I'm Mike. I've been a union lineman in New Jersey for 22+ years. I see outages that last long enough for the house to go cold on ordinary work weeks, and I've done mutual aid in multiple states. So can you run a propane heater inside? The experts split, and I'm not going to paper over it.

What the Red Cross says

The American Red Cross advises against it. Its winter storm tips (American Red Cross of Southern Colorado, January 2026) say: "Never use a generator, grill, camp stove or other gasoline, propane, natural gas or charcoal-burning devices inside a house, garage, basement, crawlspace or any partially enclosed areas." A propane heater is a propane-burning device.

What the manual says

The Mr. Heater Portable Buddy (MH9BX) owner's manual labels it a heater "for recreational, commercial and emergency indoor use." It says the heater "may be used for emergency indoor heating when connected to a disposable 1 lb. propane cylinder." The same manual calls it an unvented heater that "uses air (oxygen) from the area in which it is used," and says in capital letters, "NEVER OPERATE THE HEATER WHILE SLEEPING!"

The US manual also says it's not for use in a "dwelling home" in California. Check your state.

My take on why the Red Cross says no: too many people skip the safety steps, like the ventilation, the CO alarm, and the tank staying outside. The blankets-and-one-room plan comes first, because it's what the Red Cross points you to and it costs nothing. If you decide to use an indoor-rated heater anyway, the manual is the minimum, not a suggestion. Follow all of it, not just the convenient parts.

Step one has no flame

The safest heat in an outage is the heat your body already makes. Pick one small room and shut the door. Hang a blanket over the window and lay a rolled towel along the bottom of the door. Everybody in layers, hats, and dry socks.

Know where you'd go if it gets too cold. The Red Cross suggests a friend's house, a public library, or a warming center.

The 20 lb tank stays outside

A common answer online is to skip the hose and just bring the 20 lb tank inside. The Buddy manual says the opposite: "DANGER: NEVER bring a refillable propane cylinder indoors." A remote 20 lb tank is only allowed when the cylinder is outdoors, on Mr. Heater's listed hose, and the manual lists that hookup for recreational enclosures. Its emergency indoor heating line names the disposable 1 lb cylinder.

So indoors, only the 1 lb cylinders the manual allows. Swapping one means shutting the heater off, letting it cool, and stepping outside to change it.

Ventilation, and what the sensor doesn't do

An indoor-rated propane heater burns the oxygen in the room and gives off combustion gases and water vapor. The oxygen depletion sensor (ODS) is designed to shut the heater down when oxygen drops too low. That's a safety feature, not permission to run it in a sealed room. It also doesn't measure carbon monoxide. A low-oxygen shutoff is not a CO alarm.

The current Buddy manual asks for a vent area of at least 9 square inches, about a 3 by 3 inch opening, at the ceiling and at floor level, and says not to use other fuel-burning appliances inside.

Outdoor, patio, and construction heaters never come inside, cracked window or not. And don't heat with the gas oven or stovetop (Ready.gov).

Not overnight, either. The manual says never run it while sleeping and not to leave it unattended. Warm the room in the evening, turn the heater off at bedtime, and let the layers and sleeping bags carry you to morning.

CO alarms are part of the plan

Put CO alarms on every level and outside the sleeping areas before heater season, plus one in the room where any fuel-burning heater runs. Test them before you light anything.

Check the power. Kidde's manual for one of its plug-in models calls its 9V battery "short term back-up during a power outage." For a long outage, have at least one alarm that runs on AA batteries or a sealed 10-year battery.

If anyone gets a headache, dizziness, nausea, or a flu-like feeling that clears when they go outside, get everyone out and call 911. If you smell rotten eggs, shut the valve, get everyone out, and call your gas supplier or the fire department from outside.

What I lean on instead

For my own house, I lean on electric heat instead of a flame. During outages I've run oil-filled electric heaters off my outdoor generator. I've used a De'Longhi Dragon Digital (TRD40615 series) and an Amazon Basics 7-fin 1,500W, and both do the job well. Just size the heaters to what your generator or power supply can actually carry.

Most gas furnaces need electricity for the blower and controls, so a dead grid means a dead furnace even with gas in the line. At my house the furnace and the freezers run off that outdoor gas generator, and an EcoFlow DELTA 3 Ultra stays indoors for the internet and a few electronics. I don't ask the power station to run a space heater all night. A space heater on its 1,500-watt setting uses about 1,500 watt-hours every hour, so a 2,000 watt-hour station would run it a little over an hour before inverter losses. Run your own numbers in the power station runtime calculator, and see generator vs power station for which tool does which job.

If a generator feeds your furnace or anything else through the house wiring, the main breaker has to be open first. Otherwise its power goes back out through the service drop to the transformer and onto the lines, where it can hurt the lineman working to get you back on. Use an electrician-installed transfer switch or interlock, and never backfeed through a dryer outlet.

Hold the heat you have

Our cabin in Pennsylvania gets cold to the core in winter. When I get there, I turn on the oil-filled heaters and get a good hot fire going in the wood stove, and it can still take up to half a day to get the place somewhat comfortable, because the whole cabin is cold right down to the studs. Once the structure itself is cold, it takes a lot of heat and a lot of time to bring it back. It's better to hold heat in than to try to win it back later.

Ice takes the furnace down with the grid. The full winter plan is in the ice storm power, heat, and CO guide.

Mike Sasarak is a union electrical lineman in New Jersey with 22+ years on the job. He sees how power actually fails, and what families need when it does, on ordinary workdays, not just big name disasters.

The full guide, with the Red Cross and manual sources side by side, is on Prepper Evolution.