Last Thanksgiving, my best friend and I went on our second overlanding trip near the Sequoia National Park, California. Temperatures had dipped to as low as a bone-chilling 27F, and water bottles froze while we slept in our cars. I was a bit more comfortable than him because the Peter Pan 100oz hot water bottle and 32F-rated sleeping bag kept me warm enough. We both were thankful, however, we did not bring our young kids or the struggle would have been more difficult to handle.I looked into safe ways to keep warm a car, tent, or anything indoor, and researched the following options:- Car window insulation- Warm sleeping bag / Rubber hot water bottle- Electric blanket- Fuel-based heaterInsulating the car windows would provide an immediate boost to keep warmth from escaping, but that would have been impractical for tents. Warmer sleeping bags and hot water bottles are extremely safe options but would only help individuals that had them. Electric blankets could pose a small risk of fire or injury, require a lot of battery power to operate, and are not quite energy efficient. For warming a larger room or groups of people, I had decided on fuel-based heaters instead.ARE PORTABLE HEATERS SAFE?there are two, immediate risks and concerns with fuel-based heaters:- Carbon monoxide (CO) poisoning- Fire or burns when tipped over or flammable material accidentally touching the heating elementsAre any safe for indoor use? Yes and no. They can be safe with the proper precautions and preparations. There always, ALWAYS is a risk of fire and gas poisoning, but overwhelmingly, the Mr. Heater Buddy series was the most recommended appliance for indoor/outdoor use for a variety of reasons. Nonetheless, the Mr. Heater is NOT 100% safe.IN A NUTSHELLThe Mr. Heater Buddy series had been among the most-recommended, portable warmers rated for safe indoor and outdoor use. With proper preparations and precautions, that can certainly be the case even when no heater is 100% safe. Safety features like tip-over and low-oxygen sensors, along with a slightly open window and a separate carbon monoxide detector, can add to peace of mind while camping or staying in an enclosed space.Our Buddy MH9BX (F232000) model heated up very quickly with a standard 16oz/1 lb propane fuel canister and is rated to last between 3-6 hours. Longer runtimes can be achieved by attaching to a larger cylinder with an optional hose assembly. The fold-down carry handle can have a battery-operated stroller fan clipped on for more even heat distributionAs previously stated, no heater is 100% safe. For instance, the tip-over sensor may not activate in certain situations, the low-oxygen detector cannot read potentially deadly carbon monoxide (CO) levels, and the grid cage is too wide apart to prevent smaller, flammable materials from slipping through and catching on fire. Furthermore, the lack of a built-in CO alarm makes us strongly recommend bringing along 1 or 2 detectors (preferably with a fire alarm combo) to be on the safe side. Lower oxygen levels at elevations above 7,000′ may also render the heater from working. Mr. Heater Buddy warms quickly and could sometimes get too hot even at the lowest level.A heater provides much comfort and can even be life saving. However, we do not use our Buddy continuously throughout the night as we prefer to only turn it on when somebody is awake and able to supervise. Call us paranoid, but we would rather be safe than sorry and owe our children our trust and protection. However you plan on using the heater, always keep safety in mind. With that said, Mr. Heater had become a luxury we would not go camping without when temperatures could dip as low as 28F! Be safe and stay warm!PROS- Can safely be used indoor when adequate airflow is provided and proper precautions have been made (see TIPS section)-- Tip-over sensor to immediately stop fuel when the heater falls over (you can hear the switch activating)-- Low-oxygen sensor-- Grid cage to keep flammable material (or your kids’ hands) from touching the heating elementsCAUTION: Always leave a window or tent cracked open by at least 1″ (4 square inches) to allow for adequate air flow. Keep flammable material away from the heater.- Heats up very quickly-- Can get too hot even at the lowest setting-- Outputs 4,000 – 9,000 BTU--- Suitable for up to 225 sq ft, according to the manufacturer- Dedicated slot for holding a fuel canister-- Propane gas regulator swivels out to allow canister to screw on more easily- Uses standard 16oz/1 lb Propane Fuel Canisters-- Single tank can operate for 2.5 – 3 hours on maximum heat, the manufacturer claims, and up to 6 hours on minimum--- Mr. Heater provided this burn rate: 0.044 gal/hr @ 4,000 BTU and 0.099 gal/hr @ 9,000 BTU---- Converts to: 5.632 oz/hr @ 4,000 BTU and 12.672 oz/hr @ 9,000 BTU----- In other words, a 16oz canister can mathematically fuel for 2.84 hours on the lowest setting and 1.25 hrs at the highest----- If my math is correct, that is half of the company’s run time claim. Maybe the provided burn rate is just a conservative estimate?--- Owners on the internet had claimed 3-5 hours of continuous use from a single 16oz canister---- I did not run mine long enough to verify their claims as I do not use the heater continuously (see TIPS section)- Can be connected to larger propane cylinders via an optional hose assembly-- Mr. Heater strongly recommends their official 10′ Hose Assembly (#F273704)- Fold-down handle for carry or hangingCONS- No heater is 100% safe, Mr. Heater included-- Heat will always have a risk of fire. Burnt fuel will always come with a chance of carbon monoxide poisoning- May provide false sense of safety despite multiple protection mechanisms-- Tip-over sensor does not activate until past a certain angle. Could potentially leave heater running despite having tipped over--- Example: Heater falls over onto a mattress and remains propped up enough for the tip-over sensor not to shut off fuel-- Grid cage designed to keep heating elements from being touched is spaced too wide apart--- Piece of flammable material may potentially slip through and burn-- No built-in carbon monoxide (CO) alarm--- CO is odorless (cannot easily be smelled) and could unknowingly build up to deadly levels---- Tip: Leave a window or tent cracked open by at least 1″ (4 square inches) to allow for enough air circulation. Bring 1 or 2 reliable CO detectors (ideally with fire alarm combo) and place them properly--- Propane could leak through a faulty regulator or optional hose attachment-- Low-oxygen sensor will NOT protect against CO poisoning--- Only detects low oxygen level and not how much CO is in the air- Heater may shut off at altitudes over 7,000′ above sea due to lower oxygen levels at that elevation- May not last all night on a single, 16oz/1 lb propane canister- Can get too hot even at the lowest setting- BulkyTIPSSAFETYIt is absolutely important to take great care and proper precautions when using a fuel-burning heater. No heater is 100% safe.- Keep flammable material away from the heater-- I place Mr. Heater on top of a raised platform, like a small table, to keep things away--- Helps ensure the tip-over sensor shuts off the fuel if heater falls off. Note: heater is still hot when it trips over-- I had also bungee-corded the heater to one of the inside walls of a sturdy, plastic milk crate (open side facing up) that acted as an extra buffer against accidental kicks during sleep- Crack open the window or tent by at least 1″ (4 square inches) to ensure enough oxygen flow inside- Carbon Monoxide (CO) is odorless and can silently kill you-- Bring 1 or 2 reliable CO detectors (ideally with fire alarm combo). Do not solely rely on the built-in low-oxygen sensor as it does NOT detect CO--- Use fresh batteries and test the alarm--- Do not place them directly above or near the heater. I put one up on the tent ceiling and another in a side mesh pocket-- Check for gas leaks along the connectors and hoses with a leak detector or soapy water (look for bubbles)- If connecting Buddy to a propane cylinder via an optional hose assembly, Mr. Heater strongly recommends their official 10′ Hose Assembly (#F273704). No fuel filter is needed with it-- Third party hoses could improperly allow residue to backflow and damage the heater over time. Be sure to use a fuel filter with themMYTH: CARBON MONOXIDE HEAVIER THAN AIR?I had seen a few individuals claim that carbon monoxide (CO) is heavier than air and that sleeping on the ground while camping may leave you exposed to the deadly gas sinking onto you. As much as that sounds reasonable, both the Environmental Protection Agency (EPA) and Google Nest state that CO is actually “slightly lighter than air and diffuses evenly throughout the room.” In other words, CO rises, spreads, and does not entirely drop onto the floor. Nonetheless, bring 1 or 2 reliable CO detectors (ideally ones with a fire alarm combo) to be on the safe side.WE DO NOT HEAT WHILE SLEEPINGCall us paranoid, especially my wife, despite having made all the safety precautions. There could always be a potential for something to go wrong while sleeping in confined spaces like a tent. As such, we generally do not leave the heater running while asleep. Here is what we do instead:- Turn on when we are ready to go to sleep. Makes the tent nice and toasty for the family, especially the kids- Before the last person goes to sleep, turn off Mr. Heater-- We set an alarm in case that person accidentally fell asleep- If it gets too cold again, turn on the heater for a few minutes until warm again, then shut off once more- Turn on when waking up so the family can get going to a nice and cozy tentAs you can see, we only activate the heater when somebody is actually awake and able to supervise. The steps may seem like a lot of work, but we rarely ever had to get up in the middle of the night to reheat. The procedure had worked well for us and for many others — even in 30F temperatures! The extra peace of mind makes for a much more enjoyable, worriless camping experience.MR. HEATER MODELS/SIZESThe model reviewed in this write-up, Mr. Heater Buddy MH9BX (F232000), outputs 4,000-9,000 BTU for 3-6 hours (according to the manufacturer) on a single 16oz/1 lb canister. It is good for a room up to 225 sq feet.- Mr. Heater Little Buddy (MH4B, F215100)-- Burns at 3,800 BTU for 5.6 hours from one (1) 16oz/1 lb canister. Good for a 96 sq ft room-- Heats at 45-degree upward angle- Mr. Heater Big Buddy (MH18B, F274800)-- Burns at 4,000-18,000 BTU. Good for a 450 sq ft room-- 1.5-6 hours from one (1) 16oz/1 lb canister, 3-12 hours from two (2) 16oz canisters, or 50-220 hours from two (2) 20lb cylinders