Is it safe to use a Mr. Heater Buddy in a tent?

Yes, while you are awake and the tent is ventilated, and never while anyone is asleep. The Buddy's own manual lists tents among the enclosures it may be used in, provided there is combustion air and ventilation, and in capital letters it says "NEVER OPERATE THE HEATER WHILE SLEEPING!" The oxygen depletion sensor does not change that, because it measures oxygen, not carbon monoxide.

What the manual actually says about tents#

The operating instructions for the Buddy (model MH9BX) settle this more precisely than any forum thread, but the relevant lines are spread over four pages.

The manual permits a tent the way it permits a fishing hut: a space you sit in, awake, with air moving through it. The "yes, it's safe" answers quote the first row and leave out the fifth.

Why an oxygen depletion sensor is not a carbon monoxide detector#

The oxygen depletion sensor (ODS) cuts the gas when oxygen falls to a set point. It does not sample carbon monoxide, and guards against it only indirectly, as a 2002 CPSC report shows. CPSC ran eight propane radiant heaters in a 100 cubic foot (2.83 cubic metre) chamber under ANSI Z21.63, the camp heater standard, which caps carbon monoxide in that room at 100 ppm and requires oxygen to stay at or above 16 percent. It found:

• The six heaters without an ODS failed. Their steady carbon monoxide peaks ran from 260 to 2,124 ppm, and CPSC reports they were capable of depleting oxygen to 13.5 to 14 percent before their flames self-extinguished.
• The two ODS heaters passed. The sensor shut them off at 18.8 to 19.6 percent oxygen, "which prevented the CO concentration from exceeding 100 ppm in the chamber". Their highest steady readings were 39 and 38 ppm.
• The link: "In general, the CO concentration did not exceed 100 ppm in the test chamber until the O2 concentration was depleted below approximately 16 percent."

So the sensor stops the heater while there is still plenty of oxygen, before its flame starves. That is the only carbon monoxide it guards against. CO that arrives without an oxygen drop, from a stove or lantern in the porch, cooling charcoal or a generator by the door, never trips it. The two ODS heaters were certified to CSA 4.98, a standard for portable heaters fitted with an ODS: a certification of the shut-off, not of sleeping beside one.

Awake and ventilated against asleep: where the line is#

The manual and CPSC draw the same line, and the reason is you rather than the heater. CPSC lists the symptoms as headache, dizziness, weakness, nausea, vomiting, sleepiness and confusion, says poisoning "is often detected too late", and warns: "Do not use fuel burning portable heaters or lanterns while sleeping in enclosed areas such as tents, campers, and other vehicles."

Each symptom warns only someone awake to notice it. Sleepiness in a tent at night looks like bedtime. CPSC adds that alcohol and drug use "may compromise the ability to recognize symptoms".

• Acceptable: awake, sitting up, on a firm level base, vents open, taking the chill off while you change or read.
• Not acceptable: anyone asleep with it lit, including "just while I drop off", on LO, or with the door cracked.
• The grey zone: leaving it on because the ODS will shut it off. A sensor tripping after the heater has taken two points of your oxygen is the system working, not a licence to sleep through it.

CPSC names infants, the unborn child of a pregnant mother, the elderly, smokers and people with anaemia or heart disease as especially vulnerable, and the manual adds people at high altitudes. A sleeping child is the clearest case against an overnight heater; the rest of that routine is in camping with young children.

Ventilation arithmetic: how much air a 9,000 Btu heater needs#

"Ventilated" means nothing until it has a number, and nobody publishes air change rates for tents. The CPSC report supplies the other half: its model assumes a propane heater consumes oxygen at 2 cubic feet per hour for every 1,000 Btu per hour burned. The steady oxygen level in a ventilated space then follows:

steady oxygen percent = 20.9 minus 100 times (oxygen used per hour divided by fresh air per hour)

By it, CPSC's 100 cubic foot room at 0.5 air changes per hour can take no more than about 1,220 Btu per hour before oxygen drops below 16 percent. The Buddy runs at 4,000 or 9,000. Below, the model for a small tent of 2.8 cubic metres (a 2.1 by 1.35 metre floor, 1 metre average height, the chamber's volume) and a family tent of 8.

A sealed small tent trips the sensor in minutes. With no air exchange, 2.8 cubic metres of air holds about 590 litres of oxygen. Going from 20.9 to 19 percent removes about 54 litres: roughly 6 minutes on HI, 14 on LO. CPSC's two ODS heaters, at 0.5 to 1.5 air changes per hour, shut off after 7 to 16 minutes.

A heater that keeps shutting off is not faulty. The tent is below the air flow in the table, and the manual's troubleshooting answer is a minimum 9 square inch fresh air opening. The fix is more air.

Nine square inches is an opening, not a flow. Passing 26.8 cubic metres an hour through 58 square centimetres means air moving through the gap at about 1.3 metres per second, continuously. That depends on wind and on a low inlet plus a high outlet, the cross flow principle in tent condensation. One vent with no second opening moves far less air than its size suggests.

The model tracks oxygen only and we apply it as if tent air were evenly mixed, so it shows why a tent needs far more air than most people leave, not that any particular tent is safe.

Why the tent is only warm while the heater runs#

The warmth vanishes minutes after switching off, which is why people want to leave it on. The air in a 2.8 cubic metre tent weighs about 3.4 kg, and warming it 15 degrees C takes 3.4 times 1,005 joules per kilogram per kelvin times 15, about 51 kilojoules: 20 seconds of the Buddy's 2,640 watts on HI. The heater is replacing losses through the walls, not storing warmth. A warm night depends on keeping your own 73 watts inside the bag and off the ground, which why you sleep cold ranks fix by fix.

A second cost: propane burns as C3H8 plus 5 O2 giving 3 CO2 plus 4 H2O, so every 44 g of propane makes 72 g of water, and a 1 lb (454 g) cylinder makes about 740 g. At up to 3 hours per cylinder on HI that is roughly 250 g of vapour an hour, against 40 to 70 g an hour for one resting adult. It condenses on the fly and the bags once the heater goes off.

Carbon monoxide or carbon dioxide: which one it is#

Both. The equation above is complete combustion, whose products are carbon dioxide and water, and that is where "it only gives off CO2" comes from. Incomplete combustion adds carbon monoxide, and it grows as oxygen runs short: the CPSC chamber recorded hundreds of ppm, and once over 2,000, from heaters that had drawn the oxygen down. The Buddy manual names the gas directly and adds that "improper combustion can lead to carbon monoxide poisoning leading to serious injury or death."

The CO2 pages are right about the product and wrong about the danger: carbon monoxide "reduces the blood's ability to carry oxygen", in CPSC's words. In its 2003 and 2004 estimates, tents, campers and other temporary shelters accounted for about 14 percent of non-fire carbon monoxide deaths associated with consumer products, "mostly associated with gas or LP gas heaters". Its 2024 safety alert counts at least 12 deaths since 2020 associated with camping equipment including grills, lanterns and stoves.

Altitude shrinks the margin. The manual says the heater may shut off above 7,000 feet (about 2,130 metres), and CPSC says the sleeping warning "is especially important at high altitudes, where the risk of carbon monoxide poisoning is increased." The urge to bring a flame inside on a cold high camp is the one canister stoves in the cold warns about.

Check it before the trip, and in the tent#

1. Light it outdoors at home first. Confirm it lights and holds on both settings and goes out when turned off.
2. Find two openings before dark, one low and windward, one high and leeward, each at least a 7.6 cm square. A strip of tissue held at each should move.
3. Give it a firm, level base clear of bags, clothing and the tent wall. The manual warns that a bump can trigger the tip-over switch.
4. No second flame. No stove, lantern or charcoal in the porch while it runs. The sensor cannot see their carbon monoxide.
5. Treat a shut-off as information. Open up, wait the manual's five minutes, then add ventilation or stop.
6. Switch off before anyone lies down, and move it out once the wire guard, which the manual says stays hot, has cooled.

A battery carbon monoxide alarm is the only device in the tent that measures carbon monoxide at all. Alarms built to EN 50291-1 are designed for rooms in houses, as the car camping checklist notes, so treat one as a backstop for the awake hours, not a reason to sleep with the heater on.

Common mistakes#

Trusting the ODS as a CO alarm. It measures oxygen, and protects against the heater's own starved flame and nothing else in the tent.

Running LO overnight because it feels gentle. LO still needs about 12 cubic metres of fresh air an hour to stay above the trip point, and the sleeping warning has no setting attached.

Cooking and heating at once. The heater's sensor cannot see the stove's carbon monoxide. Cook outside or in an open porch, as camp stove types explains.

Using the heater to fix a cold sleep system. The tent air holds 20 seconds of its output. A better pad keeps working all night.

Explaining away a headache. CPSC advises seeing a doctor for cold or flu-like symptoms while camping.

Frequently asked questions#

Can you sleep with a Mr. Heater Buddy on in a tent?#

No. The manual says "NEVER OPERATE THE HEATER WHILE SLEEPING!" with no exception for tents, low settings or the oxygen sensor, and CPSC gives the same warning for all fuel-burning heaters in tents, campers and vehicles. Warm the tent before bed, switch off, and rely on the bag and pad overnight.

Does the Mr. Heater Buddy produce carbon monoxide?#

Yes, and its manual says so: without adequate combustion and ventilation air it "may give off excessive CARBON MONOXIDE, an odorless, poisonous gas." CPSC chamber tests found carbon monoxide generally stayed under 100 ppm until oxygen in a small room fell below about 16 percent.

Is the oxygen depletion sensor the same as a CO detector?#

No. It measures oxygen and cuts the gas when oxygen falls, which in CPSC tests happened at 18.8 to 19.6 percent. That limits the heater's own carbon monoxide. It cannot detect carbon monoxide from a stove, lantern, charcoal or generator nearby, which can raise CO without lowering oxygen enough to trip it.

How much ventilation does a propane heater need in a tent?#

The manual sets a minimum vent area of 9 square inches, about 58 square centimetres. As a flow, CPSC's oxygen model says HI needs about 27 cubic metres of fresh air an hour to stay above the sensor's trip point, 9.5 air changes an hour in a small tent, which takes a low inlet and a high outlet.

Why does my Buddy heater keep shutting off in the tent?#

Usually because the oxygen depletion sensor is doing its job: in a closed small tent, HI can take oxygen to the trip point in about six minutes. It can also be the tip-over switch or altitude above about 7,000 feet. The manual's fix is fresh air, a five minute wait and a relight.

Is it safe to use a propane heater in a tent with children?#

Only while the adults are awake and the tent is ventilated, and never with a child asleep inside. CPSC names infants among the groups carbon monoxide affects most, and a sleeping child cannot report a headache. Warm the tent before bedtime, then switch off and rely on child-sized bags and insulated mats.