What it is
The Mr. Heater Big Buddy (model MH18B) is a radiant propane heater that runs on three settings — 4,000, 9,000, or 18,000 BTU per hour — and heats up to 450 square feet. It connects to two disposable 1-pound propane cylinders for portability, or to a 20-pound tank with an optional hose for longer runtime at lower cost per hour. Piezo ignition means no matches or lighter. At full output on dual 1-pound cylinders, it runs for roughly 3 hours; on low, closer to 11.
This is the "keep one room livable" answer to energy_backup_heat — the checklist item covering what happens when the furnace stops working and the temperature in the house starts dropping. It is not a whole-house solution. It is the difference between a cold house and a livable room.
Why it works
An oxygen depletion sensor, not just a pilot light
The ODS continuously monitors the oxygen level in the room and shuts the heater off automatically before it drops to an unsafe level. This is the specific technology that separates an indoor-rated heater from an outdoor-only one — and it's why CPSC's own safety guidance treats ODS-equipped heaters as a real advance for enclosed-space heating, not a marketing label.
Tip-over shutoff
If the heater is knocked over — by a pet, a child, or someone moving through a dark house during an outage — the flame shuts off automatically rather than continuing to burn on its side.
Fuel flexibility
Small 1-pound cylinders (the kind sold at any hardware or grocery store) work for short outages. A 20-pound tank — the same size as a gas grill tank — extends runtime to days with an inexpensive hose-and-filter accessory, which matters if the outage outlasts your cylinder supply.
The one thing to know
"Indoor safe" is not the same as "safe with no ventilation." CPSC's guidance on portable propane heaters is specific: never use a fuel-burning heater while sleeping in an enclosed space, and always follow the manufacturer's ventilation instructions — cracking a window or door — even on an ODS-equipped unit. Two rules that matter more than the heater itself:
- Crack a window or door for airflow whenever the heater is running, and shut it off before anyone goes to sleep.
- Pair it with a working carbon monoxide alarm in the room — the ODS protects against low-oxygen conditions, but a CO alarm is your second, independent layer of protection. Our carbon monoxide detector review covers UL 2034-certified options and placement.
One more note before buying: Mr. Heater's own product listing restricts this model in Massachusetts, where state fire code treats unvented propane heaters differently than most states. If you're in MA, confirm your local fire marshal's guidance before purchasing an unvented propane heater for indoor use.
Alternatives worth knowing
Mr. Heater Portable Buddy ($90–$110) — the smaller sibling
Same ODS and tip-over safety technology at 4,000–9,000 BTU and 225 square feet of coverage. A reasonable choice for an apartment, a single bedroom, or a smaller backup budget. Less heat, same core safety design.
Wood stove — for a permanent, fuel-diverse solution
A properly installed and vented wood stove heats through any length of outage without a propane supply chain at all, but it's a home-modification project, not a purchase — permitting, clearances, and a chimney or vent kit are involved. Worth planning toward for a rural or long-term property; not a same-week fix.
Older or non-ODS propane heaters — avoid for indoor use
Every documented CO death CPSC investigated involving portable propane radiant heaters occurred with older, non-ODS units brought into a tent, camper, or enclosed space they were never rated for. If a propane heater's listing doesn't explicitly state an oxygen depletion sensor and an indoor-use certification, treat it as outdoor-only.
Maintenance
Store with the cylinders disconnected. Before each cold season, inspect the hose and regulator (if using a 20-pound tank connection) for cracking, and test the ODS by following the manufacturer's annual check in the manual. Keep at least two 1-pound cylinders on hand and rotate stock — propane itself doesn't expire, but the cylinders should be inspected for rust or damage.
Test the heater once, in daylight, with a window cracked, before you need it during an actual outage. This is the same principle as testing any backup system — the first time you use it should not be the emergency.
NWS recommendation
Buy the Big Buddy, keep two spare 1-pound cylinders, add a CO alarm to the room you'd heat, and test it once before winter. That's the backup-heat gap closed for most households.
View on AmazonAffiliate link — we earn a small commission at no cost to you.